Syntheses, crystal structures and magnetic properties of new oxalato-, croconato- and squarato-containing copper(ii) complexes

Abstract

The preparation and magnetic investigation of five mononuclear copper(II) complexes of formula [Cu(pyim)(C₂O₄)(H₂O)]·2H₂O (1), [Cu(pyim)(C₄O₄)(H₂O)₂]·2H₂O (2), Cu(pyim)(C₅O₅)·2.5H₂O (3), [Cu(H₂bim)(C₂O₄)(H₂O)]·H₂O (4) and [Cu(bpz)(C₅O₅)(H₂O)] (5) [pyim = 2-(2-pyridyl)imidazole, H₂bim = 2,2′-biimidazole, bpz = 2,2′-bipyrazine, C₂O₄²⁻ = dianion of oxalic acid, C₄O₄²⁻ = dianion of squaric acid and C₅O₅²⁻ = dianion of croconic acid] are reported. The crystal structures of 1, 2, 4 and 5 have been determined. The copper atom has a distorted square pyramidal geometry in this family of complexes: two nitrogen atoms from the bidentate nitrogen donor [pyim (1 and 2), H₂bim (4) and bpz (5)] and two oxygen atoms either from a chelating oxalate (1 and 4)/croconate (5) or from a monodentate squarate and a water molecule (2) build the basal plane whereas a water molecule fills the apical position (1, 2, 4 and 5). A semi-coordinated oxalate (1 and 4)/croconate (5) oxygen atom of a neighbouring molecule occupies the sixth coordination position, leading to centrosymmetric dinuclear units. Magnetic susceptibility measurements for 1–5 in the temperature range 2–290 K reveal the occurrence of weak intermolecular ferro- (1) and antiferromagnetic (2–5) interactions. The different strategies to use these neutral complexes as ligands in order to design polynuclear species are analyzed and discussed.