Poly[octaaquadi-μ-phosphato-trinickel(II)]

In the title compound, [Ni3(PO4)2(H2O)8]n, which was synthesized hydrothermally, all the Ni atoms are located in slightly distorted octahedral coordination environments. Two phosphate groups and two Ni atoms share a centrosymmetric four-membered ring and an eight-membered ring such that the four-membered ring is inside the eight-membered ring. The eight-membered rings are connected with the other Ni atoms (lying on centres of symmetry) through phosphate anions, generating a one-dimensional chain structure. Adjacent chains are connected through hydrogen bonds, forming a three-dimensional network.

In the title compound, [Ni 3 (PO 4 ) 2 (H 2 O) 8 ] n , which was synthesized hydrothermally, all the Ni atoms are located in slightly distorted octahedral coordination environments. Two phosphate groups and two Ni atoms share a centrosymmetric four-membered ring and an eight-membered ring such that the four-membered ring is inside the eight-membered ring. The eight-membered rings are connected with the other Ni atoms (lying on centres of symmetry) through phosphate anions, generating a one-dimensional chain structure. Adjacent chains are connected through hydrogen bonds, forming a threedimensional network.

Comment
In recent years, nickel phosphates as a rich class of inorganic materials, have undergone significant expansion due to their potential application (Chang et al., 2004;Gao et al., 1999;Sanz et al., 1999).
In general, current work has centered on their composite properties and the possibility of tuning their chemistry, by using effects from a wide variety of templates and of additives (Wang & Gao, 2005a;Wang & Gao, 2005b). However, investigations of new synthetic methods are still comparatively less exploited. For our interest in studying inorganic synthesis, herein we report the hydrothermal synthesis, and the crystal structure of the title compound. which is insoluble in water and in common organic solvents. It crystallizes in the monoclinic space group C2/m. The molecular structure, shown in Scheme 1, consists of three nickel ions, two phosphate ions, and eight water molecules. The PO 4 anions and the Ni cations are of normal valences, i.e. their valences are −3, and +2 respectively.
The structure of nickel(II) phosphate octahydrate is shown in Fig. 1.
Both Ni atoms have a slightly distorted octahedral geometry. Ni atoms are located in two different environments, one Ni atom is surrounded by four water molecules and the remaining coordination sites are ocuppied by two oxygen atoms of two phosphates respectively. In this case, the Ni atoms are surrounded by two phosphates. The other Ni atom and its symmetry generated mate are surrounded by two water molecules, respectively. Oxygen atoms of the phosphates occupy the remaining four sites to complete the octahedral coordination. In this condition the two Ni atoms are each surrounded by three phosphates, such that two phosphates are parallel, and antiparallel with the other phosphate.
The P atoms of the phosphates do not participate in forming coordination bonds. All the P atoms make four P-O bonds. These geometry parameters are in good agreement with the reported results (Ke et al., 2001). The Ni-O(water) bond lengths are within the reported range (Kuratieva et al., 2003).
The phosphate anion coordinates to two metal atoms in a chelating form with two oxygen atoms. A further bridge is to the third metal ion with one of the remaining oxygen atoms.
Two phosphate and two Ni atoms share a four-membered ring, and an eight-membered ring such that the four membered ring is inside the eight membered ring. In the four membered rings, the Ni-Ni distance is 2.909 Å, while the distance between the Ni forming the four-membered rings and the Ni adjacent to the four-membered rings is 8.059 Å. The eight membered rings are connected with third symmetry-generated nickel atom linked through phosphate anions to provide an one dimensional chain structure. Adjacent chains were connected through hydrogen bonds to provide three-dimensional network topology, which is shown in Fig. 2. supplementary materials sup-2 Experimental All reagents and solvents were used as received.

Refinement
Hydrogen atoms bound to water molecules were located in the Fourier difference map, and their distances were fixed, and subject to an O-H = 0.85 Å with deviation of positive and negative 0.01 Å restraint. The coordinates of the water H atoms were localized by applying the HYDROGEN program (Nardelli, 1999).

Poly[octaaquadi-µ-phosphato-trinickel(II)]
Crystal data [Ni 3 (PO 4  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq In the paper by Shouwen, Wang, Gao, Wen & Zhou [Acta Cryst. (2008), E64, m259], the name of the first author is given incorrectly. The correct name should be Shouwen Jin, as given above.
addenda and errata