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 [Cu2(Lpy)(H2O)2]·10H2O (1) and [Pd2(Lpy)]·4H2O (2) are formed. The complexes were structurally characterized by X-ray crystallography. The two complexes crystallize in the triclinic system with space group P1¯. 1: a = 8.829(2), b = 9.080(2), and c = 12.414(3) Å; α = 76.50(3), β = 79.12(3), and γ = 87.25(3)°; V = 950.3(4) Å3 and Z = 1 and 2: a = 8.638(2), b = 10.009(2), and c = 10.448(2) Å; α = 78.03(3), β = 69.66(3), and γ = 71.20(3)°; V = 797.2(3) Å3 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 Lpy 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 Lpy. The intra-dimeric M(1)⋯M(1A) distances in 1 and 2 are 6.9680(17) and 6.7345(18) Å, 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⋯M distances are 6.574 and 5.890 Ǻ for 1 and 2, respectively) and X-ray crystal structures.