Influence of Copper(II) and Nickel(II) Ions in the Topology of Systems Based on a Flexible Bis-Oxamate and Bipyridine Building Blocks

Single crystals of the mononuclear
bis-oxamate nickel­(II) complex
[Ni­(bipy)­(H2edpba)]·dmso (1) are obtained
by reacting [Ni­(bipy)­Cl2]·H2O and the flexible
K2(H2edpba) ligand [bipy = 2,2′-bipyridine; H4edpba = N,N′-2,2′-ethylenediphenylenebis­(oxamic acid)].
The reaction of 1 with copper­(II) ions resulted in two
products in which the replacement of the nickel­(II) ion by copper­(II)
took place: the chain compound [Cu­(bipy)­(H2edpba)]n·3nH2O·ndmso [dmso = dimethyl sulfoxide] (2) and the
analogous chain compound without dmso crystallization molecules [Cu­(bipy)­(H2edpba)]n·1.5nH2O (3a) in its polycrystalline form. The
reaction of [Cu­(bipy)­Cl2] and K2(H2edpba) yielded single crystals of [Cu­(bipy)­(H2edpba)]n·1.5nH2O
(3b). The H2edpba2– ligand
exhibits the anti conformation in 1, 2, and 3b, but it adopts different coordination
modes: terminal bis-bidentate (1) and bridging bis-bidentate
(2 and 3b) through the two pairs of carbonyl-oxygen
atoms of the two oxamate arms. Magnetic susceptibility measurements
carried out on a polycrystalline sample of 3b in the
temperature range 1.9–295 K showed the occurrence of very weak
intrachain antiferromagnetic interactions [J = −0.40
cm–1, the Hamiltonian being defined as H = −J ∑iSi·Si+1], in agreement with the large values of the copper–copper
separation [8.308(3) Å].