Di-μ3-chlorido-1:2:3κ3 Cl;2:3:4κ3 Cl-di-μ2-chlorido-1:2κ2 Cl;3:4κ2 Cl-tetra-kis-[(4-amino-1,5-dimethyl-2-phenyl-2,3-di-hydro-1H-pyrazol-3-one-κ2 N 4,O)chlorido-cadmium(II)] 1.7-hydrate: a new six-coordinate geometry index, τ6.

The title centrosymmetric tetra-nuclear cadmium(II) com-plex of 4-amino-anti-pyrine and chloride ions, [Cd4Cl8(C11H13N3O)4]·1.7H2O, was synthesized using methanol as solvent. The two independent Cd2+ ions in the asymmetric unit have different geometries; the outer Cd atoms have fivefold CdONCl3 coordination spheres, while the inner Cd atoms have sixfold CdONCl4 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 Ow-H⋯Cl (w = water) hy-dro-gen bonds link the com-ponents to form chains propagating along the a-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, τ6, is proposed to qu-anti-tatively estimate the geometry of a sixfold coordinated atom.