Synthesis and structural characterisation of the isotypic complexes (ML2)-L-II(py)(2)center dot 2H(2)O (M = Cu, Zn); the interplay of lattice imposedligand disposition and Jahn-Teller distortions [HL = 5-(4-methoxyphenyl)pyrazole-3-carboxylic acid]

The mononuclear complexes of general formula ML2(H2O)(2) (M = Zn, Cu, Ni, C o) and ML2(py)(2). 2H(2)O (M = Zn, Cu, Co) have been prepared [HL = 5-(4-me thoxyphenyl)pyrazole-3-carboxylic acid, py = pyridine]. The crystal structu res of ZnL2(py)(2). 2H(2)O and CuL2(py)(2). 2H(2)O have been determined and are isotypic. Two independent molecules are present in the structures, bot h of which are pseudo-octahedral with mutually tuans stereochemistries. In the zinc case the two metal coordination environments differ only slightly and these differences are probably due to packing forces, but for copper th e differences are greater and indicate that the direction of the Jahn-Telle r distortion observed is dependent upon the subtle constraints imposed by t he lattice. The occurrence of such molecular forms is unique for such donor sets and allows a special opportunity to observe the interplay of Jahn-Tel ler effects and packing forces.