Water of crystallization

{{Short description|Water molecules present inside crystals}} In chemistry, '''water(s) of crystallization''' or '''water(s) of hydration''' are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions.<ref>{{Greenwood&Earnshaw2nd}}</ref> In some contexts, water of crystallization is the total mass of water in a substance at a given temperature and is mostly present in a definite (stoichiometric) ratio. Classically, "water of crystallization" refers to water that is found in the crystalline framework of a metal complex or a salt, which is not directly bonded to the metal cation. <!--Mostly, the term is limited to non-coordinated (interstitial) water. '''Coordinated''' '''water''' is directly bonded to a central atom on a lattice point. Other types of water that may be present in a crystal are '''anion water''' (with hydrogen bonds to anions),<ref>Example: [https://dx.doi.org/10.1016/S0008-8846(01)00675-5 ''Anion water in gypsum (CaSO₄·2H₂O) and hemihydrate (CaSO₄·{{1/2}}H₂O)'']</ref> '''lattice water''' (no direct bonding with an ion) and '''constitution water''' (water present as hydroxyl groups). '''Zeolite water''' is water that occupies vacancies (empty sites in the crystal lattice) and may be removed without changing the crystal structure.<ref>Hiroaki Masuda, Kō Higashitani, Hideto Yoshida: [https://books.google.com/books?id=ASGBy82J9LUC&pg=PA265 ''Powder technology handbook''] CRC Press, 2006 (google books)</ref><ref>Kazuo Nakamoto: [https://books.google.com/books?id=IQZKdQ1rSKQC&pg=PA57 ''Infrared and Raman Spectra of Inorganic and Coordination Compounds Part B''] Wiley-Interscience, 2009 pp. 57–60 (google books)</ref><ref>Wells, A.F. (1984) ''Structural Inorganic Chemistry'', Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref> -->

Upon crystallization from water, or water-containing solvents, many compounds incorporate water molecules in their crystalline frameworks. Water of crystallization can generally be removed by heating a sample but the crystalline properties are often lost.

Compared to inorganic salts, proteins crystallize with large amounts of water in the crystal lattice. A water content of 50% is not uncommon for proteins.

==Applications== Knowledge of hydration is essential for calculating the masses for many compounds. The reactivity of many salt-like solids is sensitive to the presence of water. The hydration and dehydration of salts is central to the use of phase-change materials for energy storage.<ref>{{cite journal|doi=10.1016/j.rser.2007.10.005|title=Review on thermal energy storage with phase change materials and applications|year=2009|last1=Sharma|first1=Atul|last2=Tyagi|first2=V.V.|last3=Chen|first3=C.R.|last4=Buddhi|first4=D.|journal=Renewable and Sustainable Energy Reviews|volume=13|issue=2|pages=318–345|bibcode=2009RSERv..13..318S }}</ref>

== Position in the crystal structure == [[File:H-bondingFeSO47aq.tif|thumb|upright=1.6|Some hydrogen-bonding contacts in {{chem2|FeSO4*7H2O}}. This metal aquo complex crystallizes with water of hydration, which interacts with the sulfate and with the {{chem2|[Fe(H2O)6](2+)}} centers.]] A salt with associated water of crystallization is known as a '''hydrate'''. The structure of hydrates can be quite elaborate, because of the existence of hydrogen bonds that define polymeric structures.<ref>{{cite journal | url=http://pubs.acs.org/doi/abs/10.1021/ic025915o | doi=10.1021/ic025915o | title=Novel Hydrogen-Bonded Three-Dimensional Networks Encapsulating One-Dimensional Covalent Chains: [M(4,4′-bipy)(H₂O)₄](4-abs)₂·''n''H₂O (4,4′-bipy = 4,4′-Bipyridine; 4-abs = 4-Aminobenzenesulfonate) (M = Co, ''n'' = 1; M = Mn, ''n'' = 2) | year=2002 | last1=Wang | first1=Yonghui | last2=Feng | first2=Liyun | last3=Li | first3=Yangguang | last4=Hu | first4=Changwen | last5=Wang | first5=Enbo | last6=Hu | first6=Ninghai | last7=Jia | first7=Hengqing | journal=Inorganic Chemistry | volume=41 | issue=24 | pages=6351–6357 | pmid=12444778 | url-access=subscription }}</ref><ref>{{cite journal | doi=10.1016/j.inoche.2009.12.033 | title=Formation of 2D water morphologies in the lattice of the salt with [Cu₂(OH)₂(H₂O)₂(phen)₂]²⁺ as cation and 4,6-dimethyl-1,2,3-triazolo[4,5-d]pyrimidin-5,7-dionato as anion | year=2010 | last1=Maldonado | first1=Carmen R. | last2=Quirós | first2=Miguel | last3=Salas | first3=J.M. | journal=Inorganic Chemistry Communications | volume=13 | issue=3 | pages=399–403 }}</ref> Historically, the structures of many hydrates were unknown, and the dot in the formula of a hydrate was employed to specify the composition without indicating how the water is bound. Per IUPAC's recommendations, the middle dot is not surrounded by spaces when indicating a chemical adduct.<ref>{{cite book |last1=Connelly|first1=Neil G.|last2=Damhus|first2=Ture|last3=Hartshorn|first3=Richard M.|last4=Hutton|first4=Alan T. |title=Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005 (the "Red Book") |date=2005 |isbn= 0-85404-438-8 |page=56 |publisher=Royal Society of Chemistry |url=https://iupac.org/wp-content/uploads/2016/07/Red_Book_2005.pdf |access-date=10 January 2023}}</ref> Examples: *{{chem2|CuSO4*5H2O}} – copper(II) sulfate pentahydrate *{{chem2|CoCl2*6H2O}} – cobalt(II) chloride hexahydrate *{{chem2|SnCl2*2H2O}} – tin(II) (''or'' stannous) chloride dihydrate For many salts, the exact bonding of the water is unimportant because the water molecules are made labile upon dissolution. For example, an aqueous solution prepared from {{chem2|CuSO4*5H2O}} and anhydrous {{chem2|CuSO4}} behave identically. Therefore, knowledge of the degree of hydration is important only for determining the equivalent weight: one mole of {{chem2|CuSO4*5H2O}} weighs more than one mole of {{chem2|CuSO4}}. In some cases, the degree of hydration can be critical to the resulting chemical properties. For example, anhydrous {{chem2|RhCl3}} is not soluble in water and is relatively useless in organometallic chemistry whereas {{chem2|RhCl3*3H2O}} is versatile. Similarly, hydrated {{chem2|AlCl3}} is a poor Lewis acid and thus inactive as a catalyst for Friedel-Crafts reactions. Samples of {{chem2|AlCl3}} must therefore be protected from atmospheric moisture to preclude the formation of hydrates. [[File:Ca(aq)6 improved image.tif|thumb|Structure of the polymeric {{chem2|[Ca(H2O)6](2+)}} center in crystalline calcium chloride hexahydrate. Three water ligands are terminal, three bridge. Two aspects of metal aquo complexes are illustrated: the high coordination number typical for {{chem2|Ca(2+)}} and the role of water as a bridging ligand.]]

Crystals of hydrated copper(II) sulfate consist of {{chem2|[Cu(H2O)4](2+)}} centers linked to {{chem2|SO4(2-)}} ions. Copper is surrounded by six oxygen atoms, provided by two different sulfate groups and four molecules of water. A fifth water resides elsewhere in the framework but does not bind directly to copper.<ref>{{cite book|last1=Moeller|first1=Therald|title=Chemistry: With Inorganic qualitative Analysis|date=Jan 1, 1980|publisher=Academic Press Inc (London) Ltd|isbn=978-0-12-503350-3|page=909|url=https://books.google.com/books?id=uyjjgw_EmXEC&q=dehydration+of+copper(lI)+sulfate+pentahydrate|access-date=15 June 2014}}</ref> The cobalt chloride mentioned above occurs as {{chem2|[Co(H2O)6](2+)}} and {{chem2|Cl-}}. In tin chloride, each Sn(II) center is pyramidal (mean {{chem2|O/Cl\sSn\sO/Cl}} angle is 83°) being bound to two chloride ions and one water. The second water in the formula unit is hydrogen-bonded to the chloride and to the coordinated water molecule. Water of crystallization is stabilized by electrostatic attractions, consequently hydrates are common for salts that contain +2 and +3 cations as well as −2 anions. In some cases, the majority of the weight of a compound arises from water. Glauber's salt, {{chem2|Na2SO4(H2O)10}}, is a white crystalline solid with greater than 50% water by weight.

Consider the case of nickel(II) chloride hexahydrate. This species has the formula {{chem2|NiCl2(H2O)6}}. Crystallographic analysis reveals that the solid consists of {{nowrap|[''trans''-{{chem2|NiCl2(H2O)4]}}}} subunits that are hydrogen bonded to each other as well as two additional molecules of {{chem2|H2O}}. Thus one third of the water molecules in the crystal are not directly bonded to {{chem2|Ni(2+)}}, and these might be termed "water of crystallization".

==Analysis== The water content of most compounds can be determined with a knowledge of its formula. An unknown sample can be determined through thermogravimetric analysis (TGA) where the sample is heated strongly, and the accurate weight of a sample is plotted against the temperature. The amount of water driven off is then divided by the molar mass of water to obtain the number of molecules of water bound to the salt.

==Other solvents of crystallization== {{redirect|Solvate||Solvation}}

Water is a particularly common solvent to be found in crystals because it is small and polar. But many other solvents can be hosted in crystals, known as '''solvates'''.<ref name=Steed2009>{{cite book |last1=Steed |first1=Jonathan W. |last2=Atwood |first2=J. L. |title=Supramolecular chemistry |date=2009 |publisher=Wiley |location=Chichester, UK |isbn=9780470512340 |section=8.5.2 Types of Polymorphism |page=489 |edition=2nd |url=https://archive.org/details/supramolecularch0000stee_t6h2/page/489/mode/2up?q=solvate}}</ref><ref name=NMRCryst2009>{{cite book |editor-last1=Harris |editor-first1=Robin K. |editor-last2=Wasylishen |editor-first2=Roderick E. |editor-last3=Duer |editor-first3=Melinda J. |title=NMR Crystallography |publisher=John Wiley & Sons |publication-place=Chichester, U.K |date=2009 |isbn=978-0-470-69961-4 |section=7.3.9 Solvates and Cocrystals |pages=94–95 |url=https://archive.org/details/nmrcrystallograp0000unse/page/94/mode/2up?q=solvate}}</ref> Water is noteworthy because it is reactive, whereas other solvents such as benzene are considered to be chemically innocuous. Occasionally more than one solvent is found in a crystal, and often the stoichiometry is variable, reflected in the crystallographic concept of "partial occupancy". It is common and conventional for a chemist to "dry" a sample with a combination of vacuum and heat "to constant weight".

For other solvents of crystallization, analysis is conveniently accomplished by dissolving the sample in a deuterated solvent and analyzing the sample for solvent signals by NMR spectroscopy. Single crystal X-ray crystallography is often able to detect the presence of these solvents of crystallization as well. Other methods may be currently available.

==Table of crystallization water in some inorganic halides==

In the table below are indicated the number of molecules of water per metal in various salts.<ref>{{cite journal|author=K. Waizumi |author2=H. Masuda |author3=H. Ohtaki |title=X-Ray Structural Studies of FeBr₂·4H₂O, CoBr₂·4H₂O, NiCl₂·4H₂O, and CuBr₂·4H₂O. ''cis''/''trans'' Selectivity in Transition Metal(II) Dihalide Tetrahydrate|journal=Inorganica Chimica Acta|year=1992|volume=192|issue=2 |pages=173–181|doi=10.1016/S0020-1693(00)80756-2 }}</ref><ref>{{cite journal|author=B. Morosin|title=An X-ray Diffraction Study on Nickel(II) Chloride Dihydrate|journal=Acta Crystallographica |year=1967|volume=23|issue=4 |pages= 630–634|doi=10.1107/S0365110X67003305|bibcode=1967AcCry..23..630M }}</ref> {| class="wikitable" ! Hydrated metal halides<br/>and their formulas || Coordination sphere<br/>of the metal ||Equivalents of water of crystallization<br/> that are not bound to M || Remarks |- | Calcium chloride<br/>{{chem2|CaCl2(H2O)6}} || {{chem2|[Ca(μ\-H2O)6(H2O)3](2+)}} || {{CNone|none}} |example of water as a bridging ligand<ref>{{cite journal |last1=Agron |first1=P. A. |last2=Busing |first2=W. R. |year=1986 |title=Calcium and Strontium Dichloride Hexahydrates by Neutron Diffraction |journal=Acta Crystallographica Section C |volume=42 |issue=2 |page=14 |bibcode=1986AcCrC..42..141A |doi=10.1107/S0108270186097007 |s2cid=97718377}}</ref> |- | Calcium bromide<br/>{{chem2|CaBr2(H2O)9}} ||{{chem2|[Ca(H2O)8]}}²⁺ || style="text-align:center;" | 1 ||the most hydrated calcium halide<ref name=HenCa>{{cite journal |last1=Hennings |first1=Erik |last2=Schmidt |first2=Horst |last3=Voigt |first3=Wolfgang |title=Crystal structures of hydrates of simple inorganic salts. II. Water-rich calcium bromide and iodide hydrates: CaBr₂·9H₂O, CaI₂·8H₂O, CaI₂·7H₂O and CaI₂·6.5H₂O |journal=Acta Crystallographica Section C |date=2014 |volume=70 |issue=9 |pages=876–881 |doi=10.1107/S2053229614018002 |pmid=25186361 }}</ref> |- | Calcium iodide<br/>{{chem2|CaI2(H2O)7}} ||{{chem2|[Ca(H2O)8]}}²⁺<ref name=HenCa/> || {{CNone|none}} || bridging water ligands |- | Calcium iodide<br/>{{chem2|CaI2(H2O)8}} ||{{chem2|[Ca(H2O)8]}}²⁺<ref name=HenCa/> || style="text-align:center;" | 1 || bridging water ligands |- | Calcium iodide<br/>{{chem2|CaI2(H2O)6.5}} ||{{chem2|[Ca(H2O)8]}}²⁺<ref name=HenCa/> || {{CNone|none}} || bridging water ligands |- | Titanium(III) chloride<br/>{{chem2|TiCl3(H2O)6}} || ''trans''-{{chem2|[TiCl2(H2O)4]+}}<ref name=VX3aq6/> || style="text-align:center;" | 2||isomorphous with {{chem2|VCl3(H2O)6}} |- | Titanium(III) chloride<br/>{{chem2|TiCl3(H2O)6}} || {{chem2|[Ti(H2O)6]}}³⁺<ref name=VX3aq6/> || {{CNone|none}}||isomeric with {{chem2|[TiCl2(H2O)4]Cl}}^.2H₂O<ref>{{Greenwood&Earnshaw2nd|page = 965}}</ref> |- |Zirconium(IV) fluoride<br/>{{chem2|ZrF4(H2O)3}}||{{chem2|(μ\sF)2[ZrF3(H2O)3]2}} || {{CNone|none}}|| rare case where Hf and Zr differ<ref name="Greenwood&Earnshaw2nd|page=965">{{Greenwood&Earnshaw2nd|page=965}}</ref> |- |Hafnium tetrafluoride<br/>{{chem2|HfF4(H2O)3}}|| {{nowrap|{{chem2|(μ\sF)2[HfF2(H2O)2]}}_{{mvar|n}}({{H2O-nl}})_{{mvar|n}}}}|| style="text-align:center;" | 1||rare case where Hf and Zr differ<ref name="Greenwood&Earnshaw2nd|page=965"/> |- | Vanadium(III) chloride<br/>{{chem2|VCl3(H2O)6}} || ''trans''-{{chem2|[VCl2(H2O)4]+}}<ref name=VX3aq6/> || style="text-align:center;" | 2|| |- | Vanadium(III) bromide<br/>{{chem2|VBr3(H2O)6}} || ''trans''-{{chem2|[VBr2(H2O)4]+}}<ref name=VX3aq6>{{cite journal|doi=10.1039/DT9750000894|title=Crystal and Molecular Structures of Aquahalogenovanadium(III) Complexes. Part I. X-Ray Crystal Structure of ''trans''-Tetrakisaquadibromo-Vanadium(III) Bromide Dihydrate and the Isomorphous Chloro- Compound|year=1975|last1=Donovan|first1=William F.|last2=Smith|first2=Peter W.|journal=Journal of the Chemical Society, Dalton Transactions|issue=10|page=894}}</ref> || style="text-align:center;" | 2|| |- | Vanadium(III) iodide<br/>{{chem2|VI3(H2O)6}} || {{chem2|[V(H2O)6](3+)}} || {{CNone|none}}||relative to {{chem2|Cl-}} and {{chem2|Br-}}, {{chem2|I-}} competes poorly<br/> with water as a ligand for V(III) |- | {{chem2|Nb6Cl14(H2O)8}} || {{chem2|[Nb6Cl14(H2O)2]}} || style="text-align:center;" |4 || |- | Chromium(III) chloride<br/>{{chem2|CrCl3(H2O)6}} || ''trans''-{{chem2|[CrCl2(H2O)4]+}} || style="text-align:center;" | 2 ||dark green isomer, aka "Bjerrums's salt" |- | Chromium(III) chloride<br/>{{chem2|CrCl3(H2O)6}} || {{chem2|[CrCl(H2O)5](2+)}} || style="text-align:center;" | 1 ||blue-green isomer |- | Chromium(II) chloride<br/>{{chem2|CrCl2(H2O)4}} || ''trans''-{{chem2|[CrCl2(H2O)4]}} || {{CNone|none}} ||square planar/tetragonal distortion |- | Chromium(III) chloride<br/>{{chem2|CrCl3(H2O)6}} || {{chem2|[Cr(H2O)6](3+)}} || {{CNone|none}} ||violet isomer. isostructural with aluminium compound<ref>{{cite journal|last1=Andress|first1=K. R.|last2=Carpenter|first2= C.|title=Die Struktur von Chromchlorid- und Aluminiumchloridhexahydrat|journal=Zeitschrift für Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie|year=1934|volume=87|pages=446–463}}</ref> |- | Manganese(II) chloride<br/>{{chem2|MnCl2(H2O)6}} || ''trans''-{{chem2|[MnCl2(H2O)4]}} || style="text-align:center;" | 2|| |- | Manganese(II) chloride<br/>{{chem2|MnCl2(H2O)4}} || ''cis''-{{chem2|[MnCl2(H2O)4]}} || {{CNone|none}} ||cis molecular, the unstable trans isomer has also been detected<ref>{{cite journal|title=Crystal Structure of Manganese Dichloride Tetrahydrate|author1=Zalkin, Allan|author2=Forrester, J. D.|author3=Templeton, David H.|journal=Inorganic Chemistry|year=1964|volume=3|issue=4|pages=529–533|doi=10.1021/ic50014a017|url=http://www.escholarship.org/uc/item/7vf7p79j|url-access=subscription}}</ref> |- | Manganese(II) bromide<br/>{{chem2|MnBr2(H2O)4}} || ''cis''-{{chem2|[MnBr2(H2O)4]}} || {{CNone|none}} ||cis, molecular |- | Manganese(II) iodide<br/>{{chem2|MnI2(H2O)4}} || ''trans''-{{chem2|[MnI2(H2O)4]}} || {{CNone|none}} ||molecular, isostructural with FeCl2(H2O)4.<ref>{{cite journal |doi=10.1107/S0108270185007466|title=Structure of Manganese(II) Iodide Tetrahydrate, MnI₂·4H₂O|year=1985|last1=Moore|first1=J. E.|last2=Abola|first2=J. E.|last3=Butera|first3=R. A.|journal=Acta Crystallographica Section C |volume=41|issue=9|pages=1284–1286|bibcode=1985AcCrC..41.1284M }}</ref> |- | Manganese(II) chloride<br/>{{chem2|MnCl2(H2O)2}} || ''trans''-{{chem2|[MnCl4(H2O)2]}} || {{CNone|none}} ||polymeric with bridging chloride |- | Manganese(II) bromide<br/>{{chem2|MnBr2(H2O)2}} || ''trans''-{{chem2|[MnBr4(H2O)2]}} || {{CNone|none}} ||polymeric with bridging bromide |- | Rhenium(III) chloride<br/>{{chem2|Re3Cl9(H2O)4}} || ''triangulo''-{{chem2|[Re3Cl9(H2O)3]}} || {{CNone|none}} ||heavy early metals form M-M bonds<ref>{{cite journal |doi=10.1002/zaac.19875520908 |title=Rhenium trichloride, ReCl₃, and its 5/3-hydrate synthesis, crystal structure, and thermal expansion |date=1987 |last1=Irmler |first1=Manfred |last2=Meyer |first2=Gerd |journal=Zeitschrift für Anorganische und Allgemeine Chemie |volume=552 |issue=9 |pages=81–89 |bibcode=1987ZAACh.552...81I }}</ref> |- | Iron(II) chloride<br/>{{chem2|FeCl2(H2O)6}} || ''trans''-{{chem2|[FeCl2(H2O)4]}} || style="text-align:center;" | two || |- | Iron(II) chloride<br/>{{chem2|FeCl2(H2O)4}} || ''trans''-{{chem2|[FeCl2(H2O)4]}} || {{CNone|none}} ||molecular |- | Iron(II) bromide<br/>{{chem2|FeBr2(H2O)4}} || ''trans''-{{chem2|[FeBr2(H2O)4]}} || {{CNone|none}} ||molecular,<ref name=Kenji/> hydrates of FeI2 are not known |- | Iron(II) chloride<br/>{{chem2|FeCl2(H2O)2}} || ''trans''-{{chem2|[FeCl4(H2O)2]}} || {{CNone|none}} ||polymeric with bridging chloride |- | Iron(III) chloride<br/>{{chem2|FeCl3(H2O)6}} || ''trans''-{{chem2|[FeCl2(H2O)4]+}} || style="text-align:center;" | two ||one of four hydrates of ferric chloride,<ref name=Cotton>{{cite journal|author=Simon A. Cotton|year=2018|title=Iron(III) Chloride and Its Coordination Chemistry |journal=Journal of Coordination Chemistry| volume=71|issue=21|pages=3415–3443|doi=10.1080/00958972.2018.1519188|s2cid=105925459}}</ref> isostructural with Cr analogue |- | Iron(III) chloride<br/>{{chem2|FeCl3(H2O)2.5}} || ''cis''-{{chem2|[FeCl2(H2O)4]+}} || style="text-align:center;" | two ||the dihydrate has a similar structure, both contain {{chem2|FeCl4-}} anions.<ref name=Cotton/> |- | Cobalt(II) chloride<br/>{{chem2|CoCl2(H2O)6}} || ''trans''-{{chem2|[CoCl2(H2O)4]}} || style="text-align:center;" | two|| |- | Cobalt(II) bromide<br/>{{chem2|CoBr2(H2O)6}} || ''trans''-{{chem2|[CoBr2(H2O)4]}} || style="text-align:center;" | two|| |- | Cobalt(II) iodide<br/>{{chem2|CoI2(H2O)6}} || {{chem2|[Co(H2O)6](2+)}} || {{CNone|none}}<ref name=Lou>{{cite journal|title=Structure Cristalline et Expansion Thermique de l'Iodure de Nickel Hexahydrate" (Crystal structure and thermal expansion of nickel(II) iodide hexahydrate)|last1=Louër|first1=Michele|last2=Grandjean|first2=Daniel|last3= Weigel|first3=Dominique|journal=Journal of Solid State Chemistry|year=1973|volume=7|pages=222–228|doi= 10.1016/0022-4596(73)90157-6}}</ref>||iodide competes poorly with water |- | Cobalt(II) bromide<br/>{{chem2|CoBr2(H2O)4}} || ''trans''-{{chem2|[CoBr2(H2O)4]}} || {{CNone|none}} ||molecular<ref name=Kenji/> |- | Cobalt(II) chloride<br/>{{chem2|CoCl2(H2O)4}} || ''cis''-{{chem2|[CoCl2(H2O)4]}} || {{CNone|none}} ||note: cis molecular |- | Cobalt(II) chloride<br/>{{chem2|CoCl2(H2O)2}} || ''trans''-{{chem2|[CoCl4(H2O)2]}} || {{CNone|none}} ||polymeric with bridging chloride |- | Cobalt(II) bromide<br/>{{chem2|CoBr2(H2O)2}} || ''trans''-{{chem2|[CoBr4(H2O)2]}} || {{CNone|none}} ||polymeric with bridging bromide |- | Nickel(II) chloride<br/>{{chem2|NiCl2(H2O)6}} || ''trans''-{{chem2|[NiCl2(H2O)4]}} || style="text-align:center;" | two|| |- | Nickel(II) chloride<br/>{{chem2|NiCl2(H2O)4}} || ''cis''-{{chem2|[NiCl2(H2O)4]}} || {{CNone|none}} ||note: cis molecular<ref name=Kenji>{{cite journal |doi=10.1016/S0020-1693(00)80756-2| title=X-ray Structural Studies of FeBr₂·4H₂O, CoBr₂·4H₂O, NiCl₂·4H₂O and CuBr₂·4H₂O. ''cis''/''trans'' Selectivity in Transition Metal(II) Dihalide Tetrahydrate | year=1992 | last1=Waizumi | first1=Kenji | last2=Masuda | first2=Hideki | last3=Ohtaki | first3=Hitoshi | journal=Inorganica Chimica Acta | volume=192 | issue=2 | pages=173–181 }}</ref> |- | Nickel(II) bromide<br/>{{chem2|NiBr2(H2O)6}} || ''trans''-{{chem2|[NiBr2(H2O)4]}} || style="text-align:center;" | two|| |- | Nickel(II) iodide<br/>{{chem2|NiI2(H2O)6}} || {{chem2|[Ni(H2O)6](2+)}} || {{CNone|none}}<ref name=Lou/> ||iodide competes poorly with water |- | Nickel(II) chloride<br/>{{chem2|NiCl2(H2O)2}} || ''trans''-{{chem2|[NiCl4(H2O)2]}} || {{CNone|none}} ||polymeric with bridging chloride |- | Platinum(IV) chloride<br/>{{chem2|[Pt(H2O)2Cl4](H2O)3}}<ref>{{cite journal |doi=10.1524/zkri.1995.210.8.606|title=Crystal Structure of ''trans''-Diaquatetrachloroplatinum(IV) trihydrate, Pt(H₂O)₂Cl₄(H₂O)₃ |journal=Zeitschrift für Kristallographie - Crystalline Materials |year=1995 |volume=210 |issue=8 |page=606 |bibcode=1995ZK....210..606R |last1=Rau |first1=F. |last2=Klement |first2=U. |last3=Range |first3=K. -J. }}</ref> || ''trans''-{{chem2|[PtCl4(H2O)2]}} || style="text-align: center" | 3 || octahedral Pt centers; rare example of non-first row chloride-aquo complex |- | Platinum(IV) chloride<br/>{{chem2|[Pt(H2O)3Cl3]Cl(H2O)0.5}}<ref>{{cite journal |doi=10.1524/zkri.1995.210.8.605|title=Crystal Structure of ''fac''-Triaquatrichloroplatinum(IV) Chloride Hemihydrate, (Pt(H₂O)₃Cl₃)Cl(H₂O)_0.5 |journal=Zeitschrift für Kristallographie - Crystalline Materials |year=1995 |volume=210 |issue=8 |page=605 |bibcode=1995ZK....210..605R |last1=Rau |first1=F. |last2=Klement |first2=U. |last3=Range |first3=K. -J. }}</ref> || ''fac''-{{chem2|[PtCl3(H2O)3]+}} || style="text-align: center" | 0.5 || octahedral Pt centers; rare example of non-first row chloride-aquo complex |- | Copper(II) chloride<br/>{{chem2|CuCl2(H2O)2}} || {{chem2|[CuCl4(H2O)2]2}} || {{CNone|none}} ||tetragonally distorted<br/> two long Cu-Cl distances |- | Copper(II) bromide<br/>{{chem2|CuBr2(H2O)4}} || {{chem2|[CuBr4(H2O)2]_{''n''} }} || style="text-align:center;" | two ||tetragonally distorted<br/> two long Cu-Br distances<ref name=Kenji/> |- | Zinc(II) chloride<br/>ZnCl₂(H₂O)_1.33<ref name=Follner>{{cite journal |doi=10.1107/S0567740870004715|title=Die Kristallstruktur des ZnCl₂^.11/3HO|year=1970|last1=Follner|first1=H.|last2=Brehler|first2=B.|journal=Acta Crystallographica Section B |volume=26|issue=11|pages=1679–1682|bibcode=1970AcCrB..26.1679F }}</ref> || {{chem2|2 ZnCl2 + ZnCl2(H2O)4}} || {{CNone|none}} ||coordination polymer with both tetrahedral and octahedral Zn centers |- | Zinc(II) chloride<br/>ZnCl₂(H₂O)_2.5<ref name=Hennings/><ref>{{cite journal |doi=10.1107/S1600536814024738|title=Crystal Structures of ZnCl₂·2.5H₂O, ZnCl₂·3H₂O and ZnCl₂·4.5H₂O|year=2014|last1=Hennings|first1=Erik|last2=Schmidt|first2=Horst|last3=Voigt|first3=Wolfgang|journal=Acta Crystallographica Section E|volume=70|issue=12|pages=515–518|pmid=25552980|pmc=4257420|bibcode=2014AcCrE..70..515H }}</ref> || {{chem2|Cl3Zn(μ\-Cl)Zn(H2O)5}} || {{CNone|none}} || tetrahedral and octahedral Zn centers |- | Zinc(II) chloride<br/>{{chem2|ZnCl2(H2O)3}}<ref name=Follner/><ref name=Hennings/> || {{chem2|[ZnCl4](2-) & [Zn(H2O)6](2+)}} || {{CNone|none}} || tetrahedral and octahedral Zn centers |- | Zinc(II) chloride<br/>ZnCl₂(H₂O)_4.5 || {{chem2|[ZnCl4](2-) & [Zn(H2O)6](2+)}} || {{CNone|three}} || tetrahedral and octahedral Zn centers<ref name=Hennings>{{cite journal |last1=Hennings |first1=Erik |last2=Schmidt |first2=Horst |last3=Voigt |first3=Wolfgang |title=Crystal structures of ZnCl₂·2.5H₂O, ZnCl₂·3H₂O and ZnCl₂·4.5H₂O |journal=Acta Crystallographica Section E |date=2014 |volume=70 |issue=12 |pages=515–518 |doi=10.1107/S1600536814024738 |bibcode=2014AcCrE..70..515H |doi-access=free |pmc=4257420 }}</ref><ref name=Follner/> |- | Cadmium chloride<br/>CdCl₂·H₂O<ref name="mono">{{cite journal |author1=H. Leligny |author2=J. C. Monier |title=Structure Cristalline de CdCl₂^.H₂O |journal=Acta Crystallographica B |date=1974 |volume=30 |issue=2|pages=305–309 |doi=10.1107/S056774087400272X |bibcode=1974AcCrB..30..305L |trans-title=Crystal structure of CdCl2.H2O |language=fr}}</ref>|| ||{{CNone|none}} ||water of crystallization is rare for heavy metal halides |- | Cadmium chloride<br/>CdCl₂·2.5H₂O<ref>{{cite journal |doi=10.1107/S056774087500369X |title=Structure de CdCl₂.2,5H₂O |date=1975 |last1=Leligny |first1=H. |last2=Mornier |first2=J. C. |journal=Acta Crystallographica Section B |volume=31 |issue=3 |pages=728–732 |bibcode=1975AcCrB..31..728L }}</ref> || CdCl₅(H₂O) & CdCl₄(H₂O)₂ || {{CNone|none}} || |- | Cadmium chloride<br/>CdCl₂·4H₂O<ref name="tet">{{cite journal |author1=H. Leligny |author2=J. C. Monier |title=Structure de dichlorure de cadmium tétrahydraté|journal=Acta Crystallographica B |date=1979 |volume=35 |issue=3|pages=569–573 |doi=10.1107/S0567740879004179 |bibcode=1979AcCrB..35..569L |trans-title=Structure of Cadmium Dichloride Tetrahydrate|language=fr}}</ref> || CdCl₄(H₂O)₄ ||{{CNone|two}} || octahedral, doubly bridging chlorides |- | Cadmium bromide<br/>CdBr₂(H₂O)₄<ref>{{cite journal |doi=10.1107/S0567740878002186 |title=Structure Cristalline de CdBr₂^.4H₂O |date=1978 |last1=Leligny |first1=H. |last2=Monier |first2=J. C. |journal=Acta Crystallographica Section B |volume=34 |issue=1 |pages=5–8 |bibcode=1978AcCrB..34....5L }}</ref>|| {{chem2|[CdBr4(H2O)2}} || style="text-align:center;" |two || octahedral Cd centers |- | Aluminum trichloride<br/>{{chem2|AlCl3(H2O)6}} || {{chem2|[Al(H2O)6](3+)}} || {{CNone|none}} ||isostructural with the Cr(III) compound |- | Aluminum triiodide<br/>{{chem2|AlI3(H2O)6}} || {{chem2|[Al(H2O)6](3+)}} || {{CNone|none}} || other hydrates are known<ref name= Schmidt>{{cite journal |last1=Schmidt |first1=Horst |last2=Hennings |first2=Erik |last3=Voigt |first3=Wolfgang |title=Crystal structures of hydrates of simple inorganic salts. III. Water-rich aluminium halide hydrates: AlCl₃·15H₂O, AlBr₃·15H₂O, AlI₃·15H₂O, AlI₃·17H₂O and AlBr₃·9H₂O |journal=Acta Crystallographica Section C |date=2014 |volume=70 |issue=9 |pages=882–888 |doi=10.1107/S2053229614014302 |pmid=25186362 }}</ref> |- | Aluminum triiodide<br/>{{chem2|AlI3(H2O)15}} || {{chem2|[Al(H2O)6](3+)}} || {{CNone|9}} || other hydrates are known<ref name= Schmidt/> |- | Aluminum triiodide<br/>{{chem2|AlI3(H2O)17}} || {{chem2|[Al(H2O)6](3+)}} || {{CNone|11}} || the highest hydrate crystallized<ref name= Schmidt/> |}

==Hydrates of metal sulfates== Transition metal sulfates form a variety of hydrates. Many of them occur in nature, being the result of weathering of mineral sulfides.<ref name=asia>{{cite journal |doi=10.1016/j.jseaes.2012.11.027|title=The stability of sulfate and hydrated sulfate minerals near ambient conditions and their significance in environmental and planetary sciences|year=2013|last1=Chou|first1=I-Ming|last2=Seal|first2=Robert R.|last3=Wang|first3=Alian|journal=Journal of Asian Earth Sciences|volume=62|pages=734–758|bibcode=2013JAESc..62..734C}}</ref><ref name=Redhammer/> Many monohydrates are known.<ref name=Kieserite/>

{| class="wikitable" ! Formula of<br/> hydrated metal ion sulfate || Coordination<br/>sphere of the metal ion ||Equivalents of water of crystallization<br/> that are not bound to M ||mineral name ||Remarks |- | MgSO₄(H₂O) ||{{nowrap|[Mn(μ-H₂O)(μ₄,-κ¹-SO₄)₄]}}<ref name=Kieserite>{{cite journal|journal=Neues Jahrbuch für Mineralogie - Monatshefte|year=1991|author=Wildner, M.; Giester, G.|pages=296–306|title=The Crystal Structures of Kieserite-type Compounds. I. Crystal Structures of Me(II)SO₄·H₂O (Me = Mn, Fe, Co, Ni, Zn) (English translation)}}</ref> ||{{CNone|none}} || kieserite || see Mn, Fe, Co, Ni, Zn analogues

|- | MgSO₄(H₂O)₄ || [Mg(H₂O)₄(κ′,κ¹-SO₄)]₂ || {{CNone|none}}|| ||sulfate is bridging ligand, 8-membered Mg₂O₄S₂ rings<ref name="ReferenceA">{{cite journal|doi=10.1107/S1600536802002192|title=Zinc(II) Sulfate Tetrahydrate and Magnesium Sulfate Tetrahydrate. Addendum|year=2002|last1=Baur|first1=Werner H.|journal=Acta Crystallographica Section E|volume=58|issue=4|pages=e9–e10|doi-access=free|bibcode=2002AcCrE..58E...9B }}</ref> |- | MgSO₄(H₂O)₆ || [Mg(H₂O)₆] || {{CNone|none}}||hexahydrate || common motif<ref name=asia/> |- | MgSO₄(H₂O)₇ || [Mg(H₂O)₆] || style="text-align:center;" | one||epsomite || common motif<ref name=asia/> |- |TiOSO₄(H₂O)||[Ti(μ-O)₂(H₂O)(κ¹-SO₄)₃]||{{CNone|none}}|| ||further hydration gives gels |- | VSO₄(H₂O)₆|| [V(H₂O)₆] ||{{CNone|none}}|| ||Adopts the hexahydrite motif<ref>{{cite journal |doi=10.1021/ic00239a021|title=Synthesis and Characterization of Four Vanadium(II) Compounds, Including Vanadium(II) Sulfate Hexahydrate and Vanadium(II) Saccharinates|year=1986|last1=Cotton|first1=F. Albert|last2=Falvello|first2=Larry R.|last3=Llusar|first3=Rosa|last4=Libby|first4=Eduardo|last5=Murillo|first5=Carlos A.|last6=Schwotzer|first6=Willi|journal=Inorganic Chemistry|volume=25|issue=19|pages=3423–3428}}</ref> |- | VSO₄(H₂O)₇|| [V(H₂O)₆] ||style="text-align:center;" | one|| ||hexaaquo<ref>{{cite journal |doi=10.1021/ic00102a009 |title=Neutron and X-ray Structural Characterization of the Hexaaquavanadium(II) Compound VSO4.cntdot.7H2O |date=1994 |last1=Cotton |first1=F. Albert |last2=Falvello |first2=Larry R. |last3=Murillo |first3=Carlos A. |last4=Pascual |first4=Isabel |last5=Schultz |first5=Arthur J. |last6=Tomas |first6=Milagros |journal=Inorganic Chemistry |volume=33 |issue=24 |pages=5391–5395 }}</ref> |- |VOSO₄(H₂O)₅|| [VO(H₂O)₄(κ¹-SO₄)₄]|| style="text-align:center;" | one|||| |- | Cr(SO₄)(H₂O)₃ || [Cr(H₂O)₃(κ¹-SO₄)] || {{CNone|none}}|| ||resembles Cu(SO₄)(H₂O)₃<ref>{{cite journal|author1=Dahmen, T. |author2=Glaum, R. |author3=Schmidt, G. |author4=Gruehn, R. |title=Zur Darstellung und Kristallstruktur von CrSO₄·3H₂O|trans-title=Preparation and Crystal Structure of Chromium(2+) Sulfate Trihydrate|journal=Zeitschrift für Anorganische und Allgemeine Chemie|year=1990|volume=586|pages=141–8|doi=10.1002/zaac.19905860119}}</ref> |- | Cr(SO₄)(H₂O)₅ || [Cr(H₂O)₄(κ¹-SO₄)₂] || style="text-align:center;" | one|| ||resembles Cu(SO₄)(H₂O)₅<ref>{{cite journal|author1=T. P. Vaalsta|author2=E. N. Maslen|journal=Acta Crystallogr.|year=1987|volume=B43|pages=448–454|doi=10.1107/S0108768187097519|title=Electron density in chromium sulfate pentahydrate|issue=5 |bibcode=1987AcCrB..43..448V }}</ref> |- | Cr₂(SO₄)₃(H₂O)₁₈ || [Cr(H₂O)₆] || style="text-align:center;" | six|| ||One of several chromium(III) sulfates |- | MnSO₄(H₂O) ||[Mn(μ-H₂O)(μ₄,-κ¹-SO₄)₄]<ref name=Kieserite/> ||{{CNone|none}} || szmikite || see Fe, Co, Ni, Zn analogues |- | MnSO₄(H₂O)₄ ||[Mn(μ-SO₄)₂(H₂O)₄]<ref>{{cite journal |doi=10.1107/S1600536802020962|title=Manganese(II) Sulfate Tetrahydrate (Ilesite) |year=2002 |last1=Held |first1=Peter |last2=Bohatý |first2=Ladislav |journal=Acta Crystallographica Section E |volume=58 |issue=12 |pages=i121–i123 |s2cid=62599961 |doi-access=free |bibcode=2002AcCrE..58I.121H }}</ref> ||{{CNone|none}} || Ilesitepentahydrate is called jôkokuite; the hexahydrate, the most rare, is called chvaleticeite ||with 8-membered ring Mn₂(SO₄)₂ core |- | MnSO₄(H₂O)₅ || || {{dunno}} || jôkokuite || |- | MnSO₄(H₂O)₆ || || {{dunno}} || Chvaleticeite || |- | MnSO₄(H₂O)₇ || [Mn(H₂O)₆] || style="text-align:center;" | one|| mallardite<ref name=Redhammer/>||see Mg analogue |- | FeSO₄(H₂O) ||[Fe(μ-H₂O)(μ₄-κ¹-SO₄)₄]<ref name=Kieserite/> ||{{CNone|none}} || || see Mn, Co, Ni, Zn analogues |- | FeSO₄(H₂O)₇ || [Fe(H₂O)₆] || style="text-align:center;" | one|| melanterite<ref name=Redhammer/>||see Mg analogue |- | FeSO₄(H₂O)₄ || [Fe(H₂O)₄(κ′,κ¹-SO₄)]₂ || {{CNone|none}}|| ||sulfate is bridging ligand, 8-membered Fe₂O₄S₂ rings<ref name="ReferenceA"/> |- | Fe^II(Fe^III)₂(SO₄)₄(H₂O)₁₄ || {{nowrap|[Fe^II(H₂O)₆]²⁺[Fe^III(H₂O)₄(κ¹-SO₄)₂]{{su|p=−|b=2}}}} || {{CNone|none}}|| ||sulfates are terminal ligands on Fe(III)<ref>{{cite journal|title=The Crystal Structure of Roemerite |author=L. Fanfani |author2=A. Nunzi |author3=P. F. Zanazzi |journal=American Mineralogist|year=1970|volume=55|pages=78–89}}</ref> |- | CoSO₄(H₂O) ||[Co(μ-H₂O)(μ₄-κ¹-SO₄)₄]<ref name=Kieserite/>||{{CNone|none}} || || see Mn, Fe, Ni, Zn analogues |- | CoSO₄(H₂O)₆ || [Co(H₂O)₆] || {{CNone|none}}||moorhouseite ||see Mg analogue |- | CoSO₄(H₂O)₇ || [Co(H₂O)₆] || style="text-align:center;" | one||bieberite<ref name=Redhammer/>||see Fe, Mg analogues |- | NiSO₄(H₂O) ||[Ni(μ-H₂O)(μ₄-κ¹-SO₄)₄]<ref name=Kieserite/> ||{{CNone|none}} || || see Mn, Fe, Co, Zn analogues |- | NiSO₄(H₂O)₆ || [Ni(H₂O)₆] || {{CNone|none}}||retgersite || One of several nickel sulfate hydrates<ref>{{cite journal | doi=10.1107/S0108768187097787 | title=Structure, absolute configuration and optical activity of α-nickel sulfate hexahydrate | year=1987 | last1=Stadnicka | first1=K. | last2=Glazer | first2=A. M. | last3=Koralewski | first3=M. | journal=Acta Crystallographica Section B | volume=43 | issue=4 | pages=319–325 | bibcode=1987AcCrB..43..319S }}</ref> |- | NiSO₄(H₂O)₇ || [Ni(H₂O)₆] || one | ||morenosite<ref name=Redhammer/> || |- | PdSO₄(H₂O)₂ || [Pd(SO₄)(H₂O)₂]<ref>{{cite journal|title=Preparation and Structure of Palladium Sulfate and Palladium Sulfate Dihydrate |last1=Korsunskii|first1=V. I|last2=Chalisova, |first2=N. N.|last3=Leonova|first3=O. G.|last4=Evstaf'eva, |first4=O. N.|journal=Zhurnal Neorganicheskoi Khimii|year=1990|volume=35|page=583-8 | language=Russian</ref> ||none || || |- | (NH₄)₂[Pt₂(SO₄)₄(H₂O)₂] || [Pt₂(SO₄)₄(H₂O)₂]^2&minus; || {{CNone|none}}|| || Pt-Pt bonded Chinese lantern structure<ref>{{cite journal |doi=10.1002/ejic.200400755|title=Monomers, Chains and Layers of [Pt₂(SO₄)₄] Units in the Crystal Structures of the Platinum(III) Sulfates (NH₄)₂[Pt₂(SO₄)₄(H₂O)₂], K₄[Pt₂(SO₄)₅] and Cs[Pt₂(SO₄)₃(HSO₄)]|year=2005|last1=Pley|first1=Martin|last2=Wickleder|first2=Mathias S.|journal=European Journal of Inorganic Chemistry|volume=2005|issue=3|pages=529–535|bibcode=2005EJIC.2005..529P |doi-access=free}}</ref> |- | CuSO₄(H₂O)₅ || [Cu(H₂O)₄(κ¹-SO₄)₂] || style="text-align:center;" | one|| chalcantite||sulfate is bridging ligand<ref>V. P. Ting, P. F. Henry, M. Schmidtmann, C. C. Wilson, M. T. Weller "In situ Neutron Powder Diffraction and Structure Determination in Controlled Humidities" Chem. Commun., 2009, 7527-7529. {{doi|10.1039/B918702B}}</ref> |- | CuSO₄(H₂O)₇ || [Cu(H₂O)₆] || style="text-align:center;" | one|| boothite<ref name=Redhammer/>|| |- | ZnSO₄(H₂O) ||[Zn(μ-H₂O)(μ₄-κ¹-SO₄)₄]<ref name=Kieserite/>||{{CNone|none}} || || see Mn, Fe, Co, Ni analogues |- | ZnSO₄(H₂O)₄ || [Zn(H₂O)₄(κ′,κ¹-SO₄)]₂ || {{CNone|none}}|| ||sulfate is bridging ligand, 8-membered Zn₂O₄S₂ rings<ref name="ReferenceA"/><ref>{{cite journal|doi=10.1107/S1600536801017998|title=Zinc(II) sulfate tetrahydrate|year=2001|last1=Blake|first1=Alexander J.|last2=Cooke|first2=Paul A.|last3=Hubberstey|first3=Peter|last4=Sampson|first4=Claire L.|journal=Acta Crystallographica Section E|volume=57|issue=12|pages=i109–i111|bibcode=2001AcCrE..57I.109B }}</ref> |- | ZnSO₄(H₂O)₆ || [Zn(H₂O)₆] || {{CNone|none}}|| ||see Mg analogue<ref>{{cite journal|doi=10.1002/zaac.19794560124|title=Beiträge zum thermischen Verhalten von Sulfaten. II. Zur thermischen Dehydratisierung des ZnSO₄·7H₂O und zum Hochtemperaturverhalten von wasserfreiem ZnSO₄|year=1979|last1=Spiess|first1=M.|last2=Gruehn|first2=R.|journal=Zeitschrift für anorganische und allgemeine Chemie|volume=456|pages=222–240}}</ref> |- | ZnSO₄(H₂O)₇ || [Zn(H₂O)₆] || style="text-align:center;" |one|| goslarite<ref name=Redhammer>{{cite journal |doi=10.2138/am.2007.2229|title=Co²⁺–Cu²⁺ Substitution in Bieberite Solid-Solution Series, (Co_1−''x''Cu_''x''SO₄·7H₂O, 0.00 ≤ ''x'' ≤ 0.46: Synthesis, Single-Crystal Structure Analysis, and Optical Spectroscopy|year=2007|last1=Redhammer|first1=G. J.|last2=Koll|first2=L.|last3=Bernroider|first3=M.|last4=Tippelt|first4=G.|last5=Amthauer|first5=G.|last6=Roth|first6=G.|journal=American Mineralogist|volume=92|issue=4|pages=532–545|bibcode=2007AmMin..92..532R|s2cid=95885758}}</ref>|| see Mg analogue |- |CdSO₄(H₂O)||[Cd(μ-H₂O)₂(κ¹-SO₄)₄]|| {{CNone|none}} || ||bridging water ligand<ref>{{cite journal|author=Theppitak, Chatphorn; Chainok, Kittipong|title=Crystal Structure of CdSO₄(H₂O): A Redetermination|journal=Acta Crystallographica Section E |year=2015|volume=71|issue=10|pages=i8–i9|doi=10.1107/S2056989015016904|pmid=26594423|pmc=4647421|doi-access=free}}</ref> |- |}

==Hydrates of metal nitrates== Transition metal nitrates form a variety of hydrates. The nitrate anion often binds to the metal, especially for those salts with fewer than six aquo ligands. Nitrates are uncommon in nature, so few minerals are represented here. Hydrated ferrous nitrate has not been characterized crystallographically.

{| class="wikitable" ! Formula of<br/> hydrated metal ion nitrate || Coordination<br/>sphere of the metal ion ||Equivalents of water of crystallization<br/> that are not bound to M ||Remarks |- | Cr(NO₃)₃(H₂O)₉ || [Cr(H₂O)₆]³⁺ || style="text-align:center;" |three|| octahedral configuration<ref>{{cite journal |doi=10.1107/S0108270190012628|title=Structure of Hexaaquachromium(III) Nitrate Trihydrate|year=1991|last1=Lazar|first1=D.|last2=Ribár|first2=B.|last3=Divjaković|first3=V.|last4=Mészáros|first4=Cs.|journal=Acta Crystallographica Section C |volume=47|issue=5|pages=1060–1062|bibcode=1991AcCrC..47.1060L }}</ref> isostructural with Fe(NO₃)₃(H₂O)₉ |- | Mn(NO₃)₂(H₂O)₄ || ''cis''-[Mn(H₂O)₄(κ¹-ONO₂)₂] || {{CNone|none}}|| octahedral configuration |- | Mn(NO₃)₂(H₂O) || [Mn(H₂O)(μ-ONO₂)₅] || {{CNone|none}}|| octahedral configuration |- | Mn(NO₃)₂(H₂O)₆ || [Mn(H₂O)₆] || {{CNone|none}}|| octahedral configuration isomorphous with Zn analogue<ref name=Petro>{{cite journal |doi=10.1524/zkri.1976.144.16.334| title=The Crystal Structure of hexaquomanganese nitrate, Mn(OH₂)₆(NO₃)₂| year=1976| last1=Petrovič| first1=D.| last2=Ribár| first2=B.| last3=Djurič| first3=S.| last4=Krstanovič| first4=I.| journal=Zeitschrift für Kristallographie - Crystalline Materials| volume=144| issue=1–6| pages=334–340| s2cid=97491858}}</ref> |- | Fe(NO₃)₃(H₂O)₉ || [Fe(H₂O)₆]³⁺ || style="text-align:center;" |three|| octahedral configuration<ref>{{cite journal |doi=10.1021/ic50168a006|title=Structure of Hexaaquairon(III) Nitrate Trihydrate. Comparison of Iron(II) and Iron(III) Bond Lengths in High-Spin Octahedral Environments|year=1977|last1=Hair|first1=Neil J.|last2=Beattie|first2=James K.|journal=Inorganic Chemistry|volume=16|issue=2|pages=245–250}}</ref> isostructural with Cr(NO₃)₃(H₂O)₉ |- | Fe(NO₃)₃)(H₂O)₄ || [Fe(H₂O)₃(κ²-O₂NO)₂]⁺ || style="text-align:center;" |one|| pentagonal bipyramid<ref name=schm2012>{{cite journal|first1=H. |last1=Schmidt |first2=A. |last2=Asztalos |first3=F. |last3=Bok |first4=W. |last4=Voigt |date=2012 |title=New iron(III) nitrate hydrates: Fe(NO₃)₃·''x''H₂O with ''x'' = 4, 5 and 6 |journal=Acta Crystallographica Section C |volume=C68 |issue=6 |pages=i29-33 |doi=10.1107/S0108270112015855|pmid=22669180 }}</ref> |- | Fe(NO₃)₃(H₂O)₅ || [Fe(H₂O)₅(κ¹-ONO₂)]²⁺ || {{CNone|none}}|| octahedral configuration<ref name=schm2012/> |- | Fe(NO₃)₃(H₂O)₆ || [Fe(H₂O)₆]³⁺ || {{CNone|none}}|| octahedral configuration<ref name=schm2012/> |- | Co(NO₃)₂(H₂O)₂ || [Co(H₂O)₂(κ¹-ONO₂)₂] || {{CNone|none}}|| octahedral configuration |- | Co(NO₃)₂(H₂O)₄ || [Co(H₂O)₄(κ¹-ONO₂)₂ || {{CNone|none}}|| octahedral configuration |- | Co(NO₃)₂(H₂O)₆ || [Co(H₂O)₆]²⁺ || {{CNone|none}}|| octahedral configuration.<ref>{{ cite journal | journal = Cryst. Struct. Commun. | first1 = P. V. | last1 = Prelesnik | first2 = F. | last2 = Gabela | first3 = B. | last3 = Ribar | first4 = I. | last4 = Krstanovic | volume = 2 | issue = 4 | year = 1973| pages = 581–583 | title = Hexaaquacobalt(II) nitrate}}</ref> |- | α-Ni(NO₃)₂(H₂O)₄ || ''cis''-[Ni(H₂O)₄(κ¹-ONO₂)₂] || {{CNone|none}}|| octahedral configuration.<ref>{{cite journal |doi=10.1107/S0365110X67001392|title=Structure du Nitrate de Nickel Tétrahydraté|year=1967|last1=Gallezot|first1=P.|last2=Weigel|first2=D.|last3=Prettre|first3=M.|journal=Acta Crystallographica|volume=22|issue=5|pages=699–705|doi-access=free|bibcode=1967AcCry..22..699G }}</ref> |- | β-Ni(NO₃)₂(H₂O)₄ || ''trans''-[Ni(H₂O)₄(κ¹-ONO₂)₂] || {{CNone|none}}|| octahedral configuration.<ref>{{cite journal |doi=10.1107/S0567740879010827|title=Crystal Structure of the β Form of Ni(NO₃)₂·4H₂O|year=1979|last1=Morosin|first1=B.|last2=Haseda|first2=T.|journal=Acta Crystallographica Section B |volume=35|issue=12|pages=2856–2858}}</ref> |- |Pd(NO₃)₂(H₂O)₂ || {{nowrap|''trans''-[Pd(H₂O)₂(κ¹-ONO₂)₂]}} || {{CNone|none}}||square planar coordination geometry<ref>{{cite journal |doi=10.1016/0025-5408(91)90021-D|title=Crystal Structure of Pd(NO₃)₂(H₂O)₂|year=1991|last1=Laligant|first1=Y.|last2=Ferey|first2=G.|last3=Le Bail|first3=A.|journal=Materials Research Bulletin|volume=26|issue=4|pages=269–275}}</ref> |- | Cu(NO₃)₂(H₂O) || [Cu(H₂O)(κ²-ONO₂)₂] || {{CNone|none}} || octahedral configuration. |- | Cu(NO₃)₂(H₂O)_1.5 || {{dunno|uncertain}} || {{dunno|uncertain}} || {{dunno|uncertain}}<ref>{{cite journal | last1 = Dornberger-Schiff | first1 = K. | last2 = Leciejewicz | first2 = J. | year = 1958 | title = Zur Struktur des Kupfernitrates Cu(NO₃)₂·1.5H₂O | journal = Acta Crystallographica | volume = 11 | issue = 11 | pages = 825–826 | doi = 10.1107/S0365110X58002322 | doi-access = free | bibcode = 1958AcCry..11..825D }}</ref> |- | Cu(NO₃)₂(H₂O)_2.5 || [Cu(H₂O)₂(κ¹-ONO₂)₂] || style="text-align:center;" |one|| square planar<ref>{{cite journal | last1 = Morosin | first1 = B. | year = 1970 | title = The Crystal Structure of Cu(NO₃)₂·2.5H₂O | journal = Acta Crystallographica | volume = B26 | issue = 9 | pages = 1203–1208 | doi = 10.1107/S0567740870003898 | bibcode = 1970AcCrB..26.1203M }}</ref> |- | Cu(NO₃)₂(H₂O)₃ || {{dunno|uncertain}} || {{dunno|uncertain}} || {{dunno|uncertain}}<ref>J. Garaj, ''Sbornik Prac. Chem.-Technol. Fak. Svst., Cskosl.'' 1966, pp. 35–39.</ref> |- | Cu(NO₃)₂(H₂O)₆ || [Cu(H₂O)₆]²⁺ || {{CNone|none}} || octahedral configuration<ref>{{cite journal | last1 = Zibaseresht | first1 = R. | last2 = Hartshorn | first2 = R. M. | year = 2006 | title = Hexaaquacopper(II) dinitrate: absence of Jahn-Teller distortion | journal = Acta Crystallographica | volume = E62 | issue = 1 | pages = i19–i22 | doi = 10.1107/S1600536805041851 | bibcode = 2006AcCrE..62I..19Z }}</ref> |- | Zn(NO₃)₂(H₂O)₄ || ''cis''-[Zn(H₂O)₄(κ¹-ONO₂)₂] || {{CNone|none}}|| octahedral configuration. |- | Zn(NO₃)₂(H₂O)₆ || [Zn(H₂O)₆] || {{CNone|none}}|| octahedral configuration isomorphous with Mn analogue<ref name=Petro/> |- | {{chem2|link=Mercurous nitrate|Hg2(NO3)2(H2O)2}} ||[H₂O–Hg–Hg–OH₂]²⁺|| style="text-align:center;" | linear<ref>{{cite journal |journal=Journal of the Chemical Society|title=The Crystal Structure of Mercurous Nitrate Dihydrate|author=D. Grdenić|doi= 10.1039/jr9560001312|year=1956|page=1312}}</ref> |- |}

== Gallery == <gallery> File:Copper sulfate.jpg|Hydrated copper(II) sulfate is bright blue. File:Copper sulfate anhydrous.jpg|Anhydrous copper(II) sulfate has a light turquoise tint. File:ICSD CollCode71346.png|Substructure of MSO₄(H₂O), illustrating presence of bridging water and bridging sulfate (M = Mg, Mn, Fe, Co, Ni, Zn). </gallery>

== See also == *Hydrate *Mineral hydration *Hydrous oxide

== References == {{reflist}}

Category:Crystallography Category:Hydrates