Synthesis and structural characterization of dicopper(II) and dipalladium(II) complexes of 1,1,2,2-tetrakis(carboxamido-2-methylpyridyl)ethane

The binucleating ligand, 1,1,2,2-tetrakis(carboxamido-2-methylpyridyl)ethane (H4Lpy) was prepared. In neutral aqueous medium the H4Lpy binds two metal(II) ions and the dinuclear complexes [Cu-2(L-py)(-H2O)(2)]center dot 10H(2)O (1) and [Pd-2(L-py)]center dot 4H(2)O (2) are formed. The complexes were structurally characterized by X-ray crystallography. The two complexes crystallize in the triclinic system with space group P (1) over bar. 1: a = 8.829(2), b = 9.080(2), and c = 12.414(3) angstrom; alpha = 76.50(3), beta = 79.12(3), and gamma = 87.25(3)degrees; V = 950.3(4)angstrom(3) and Z = 1 and 2: a = 8.638(2), b = 10.009(2), and c = 10.448(2)angstrom; alpha = 78.03(3), beta = 69.66(3), and gamma = 71.20(3)degrees; V = 797.2(3)angstrom(3) and Z = 1. The coordination polyhedron in 1 may be described as axially elongated square pyramid where the Cu(II) centers are coordinated with the four N atoms of the L-py tetraanion and an O(3) atom of the aqua ligand. In complex 2, each Pd(II) center displays a distorted square planar geometry achieved by the four N-donor atoms of L-py. The intra-dimeric M(1)center dot center dot center dot M(1A) distances in 1 and 2 are 6.9680(17) and 6.7345(18)angstrom, respectively. Molecular mechanics (MM) calculations were applied on the two complexes to determine their molecular structures in the solid state. Fair agreement was obtained between the structures predicted by MM calculations (M center dot center dot center dot M distances are 6.574 and 5.890 angstrom for 1 and 2, respectively) and X-ray crystal structures. (C) 2009 Elsevier B. V. All rights reserved.