<P> Transition metal sulfates form mono -, tetra -, and pentahydrates, each of which crystallizes in only one form . The water in these salts typically is coordinated, together with sulfate to the metal center . The sulfates of these same metals also crystallize as both tetragonal and monoclinic hexahydrates, wherein all water is coordinated and the sulfate is a counterion . The heptahydrates, which are often the most common salts, crystallize as monoclinic and the less common orthorhombic forms . In the heptahydrates, one water is in the lattice and the other six are coordinated to the ferrous center . Cr (SO) 18H O </P> <Table> <Tr> <Th> Formula of hydrated metal sulfate </Th> <Th> Coordination sphere of the metal </Th> <Th> Equivalents of water of crystallization that are not bound to M </Th> <Th> Remarks </Th> </Tr> <Tr> <Td> Cr (SO) (H O) </Td> <Td> (Cr (H O)) </Td> <Td> six </Td> <Td> one of several chromium (III) sulfates </Td> </Tr> <Tr> <Td> MnSO (H O) </Td> <Td> unknown </Td> <Td> unknown </Td> <Td> one of several manganese (II) sulfates </Td> </Tr> <Tr> <Td> FeSO (H O) </Td> <Td> (Fe (H O)) </Td> <Td> one </Td> <Td> Common motif for divalent metal sulfates </Td> </Tr> <Tr> <Td> CoSO (H O) </Td> <Td> (Co (H O)) </Td> <Td> one </Td> <Td> Common motif for divalent metal sulfates </Td> </Tr> <Tr> <Td> NiSO (H O) </Td> <Td> (Ni (H O)) </Td> <Td> one </Td> <Td> Common motif for divalent metal sulfates </Td> </Tr> <Tr> <Td> NiSO (H O) </Td> <Td> (Ni (H O)) </Td> <Td> none </Td> <Td> one of several nickel sulfate hydrates </Td> </Tr> <Tr> <Td> CuSO (H O) </Td> <Td> (Cu (H O) (SO)) </Td> <Td> one </Td> <Td> sulfate is bridging ligand </Td> </Tr> <Tr> <Td> CdSO (H O) </Td> <Td> Cd (H O) SO </Td> <Td> none </Td> <Td> bridging water ligand </Td> </Tr> </Table> <Tr> <Th> Formula of hydrated metal sulfate </Th> <Th> Coordination sphere of the metal </Th> <Th> Equivalents of water of crystallization that are not bound to M </Th> <Th> Remarks </Th> </Tr> <Tr> <Td> Cr (SO) (H O) </Td> <Td> (Cr (H O)) </Td> <Td> six </Td> <Td> one of several chromium (III) sulfates </Td> </Tr>

The compound h2o is an example of a(n)