Tetrakis(dipropylammonium) tetrakis(oxalato-κ2 O 1,O 2)stannate(IV) monohydrate: a complex with an eight-coordinate SnIV atom

In the title salt, [(CH3CH2CH2)2NH2]4[Sn(C2O4)4]·H2O, the SnIV atom of the stannate anion is located on a special position with -42m symmetry. It is eight-coordinated by four chelating oxalate anions. The dipropylammonium cation possesses mirror symmetry while the lattice water molecule is disordered about a position with -42m symmetry and has an occupancy of 0.25. In the crystal, the anions and cations are linked by N—H⋯O hydrogen bonds, forming a three-dimensional network. This network is futher stabilized by weak O—H⋯O hydrogen bonds involving the water molecules and oxalate O atoms. The crystal studied was refined as an inversion twin.

In the title salt, [(CH 3 CH 2 CH 2 ) 2 NH 2 ] 4 [Sn(C 2 O 4 ) 4 ]ÁH 2 O, the Sn IV atom of the stannate anion is located on a special position with 42m symmetry. It is eight-coordinated by four chelating oxalate anions. The dipropylammonium cation possesses mirror symmetry while the lattice water molecule is disordered about a position with 42m symmetry and has an occupancy of 0.25. In the crystal, the anions and cations are linked by N-HÁ Á ÁO hydrogen bonds, forming a threedimensional network. This network is futher stabilized by weak O-HÁ Á ÁO hydrogen bonds involving the water molecules and oxalate O atoms. The crystal studied was refined as an inversion twin.

Comment
The chemistry and applications of organotin(IV) complexes have been extensively discussed by Evans & Karpel (1985).
Continuing our interest in Sn IV oxalate complexes (Gueye et al., 2010), we studied the reaction of dipropylammonium oxalate with SnBr 2 , and report herein on the crystal structure of the title compound, The molecular structure of the title salt is illustrated in Fig. 1. The Sn IV atom of the stannate anion is located on a special position with 42m symmetry. It is chelated by four bidentate oxalate ions, each lying in a mirror plane, and hence has a coordination number of eight. This coordination number has also been reported for some zirconium complexes, viz. bis-(4,4′-bipyridinium) tetrakis(oxalato-κ 2 O,O′)zirconate(IV) (Fu et al., 2005), or several salts with general composition (Imaz et al., 2007). In the crystal of the title salt, the stannate(IV) anions are linked via N-H···O hydrogen bonds to the [(CH 3 CH 2 CH 2 ) 2 NH 2 ] + cations (which have mirror symmetry), forming a three-dimensional network. The water molecule (disordered about a position with 42m symmetry), is also involved in weak O-H···O hydrogen bonds with the stannate(IV) anions, hence futher stabilizing the three-dimensional network (Fig. 2).

Experimental
The title compound was prepared by reacting in a 1:1 molar ratio of SnBr 2 and (Pr 2 NH 2 ) 2 ·C 2 O 4 in methanol. The solution was allowed to stand and yielded colourless block-like crystals of the title compound. The proof of the presence of the tin atom was confirmed by the structure analysis and by electron dispersive X-ray (EDX) analysis.

Figure 1
A view of the molecular components of the title salt. Displacement ellipsoids are drawn at the 50% probability level.   Table 1 for details; C-bound H atoms have been omitted for clarity).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refined as a 2-component inversion twin.