Di-μ-chlorido-1:2:3κ ;2:3:4κ -di-μ-chlorido-1:2κ ;3:4κ -tetra-kis-[(4-amino-1,5-dimethyl-2-phenyl-2,3-di-hydro-1-pyrazol-3-one-κ ,)chlorido-cadmium(II)] 1.7-hydrate: a new six-coordinate geometry index, τ.

The title centrosymmetric tetra-nuclear cadmium(II) com-plex of 4-amino-anti-pyrine and chloride ions, [CdCl(CHNO)]·1.7HO, was synthesized using methanol as solvent. The two independent Cd ions in the asymmetric unit have different geometries; the outer Cd atoms have fivefold CdONCl coordination spheres, while the inner Cd atoms have sixfold CdONCl coordination spheres. The com-plex is consolidated by intra-molecular N-H⋯O and N-H⋯Cl hy-dro-gen bonds. In the crystal, a combination of N-H⋯Cl and O-H⋯Cl (w = water) hy-dro-gen bonds link the com-ponents to form chains propagating along the -axis direction. The chains are crosslinked by C-H⋯Cl and C-H⋯O hy-dro-gen bonds to form a three-dimensional structure. A new geometry index, τ, is proposed to qu-anti-tatively estimate the geometry of a sixfold coordinated atom.