CuSO4.3HzO crystallizes in space group Cc with a= 5.592, b= 13.029, c=7.341 A, B= 97°3 ', Z=4. The structure has been determined from Patterson and Fourier syntheses using three-dimensional data collected on a precession camera with Mo Ke radiation. The structure was refined by the method of least squares. The final R value for 936 observed structure factors is 0.069. The coordination polyhedra around the Cu2+ ions do not share any edges or corners with each other; they are connected by hydrogen bonds and via linking sulfate groups. The square planar coordination around the copper ion consists of three water oxygen atoms and one sulfate oxygen atom at an average distance of 1.96/~. Two more sulfate oxygen atoms at 2.40 and 2.45 A, complete the distorted octahedral coordination. The average S-O bond length in the sulfate tetrahedron is 1.472 A. The positions of the hydrogen atoms were not determined experimentally; they were calculated theoretically assuming that the hydrogen atoms are in positions of least electrostatic energy. Only four of the six crystallographically nonequivalent hydrogen atoms are involved in normal hydrogen bonds.

A stereochemical model based on nonbonded intramolecular van der Waals interactions is presented and is shown to account for the observed bond angles and bond lengths in monodentate complexes which have tin as a central atom. The model is applied to several mononuclear complexes of tin that have been studied by X-ray diffraction: SnCl4;2POCl3, SnCl4-2SeOCl2, SnCl4-2(CH3)2SO, SnCl4-2CH3CN, (CH3)2SnCl2-2(CH3)2SO, (CH3)2-(1)

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