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