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

The preparation and magnetic investigation of five mononuclear copper(II) complexes of formula [Cu(pyim)(C2O4)(H2O)].2H(2)O (1), [Cu(pyim)(C4O4)(H2O)(2)].2H(2)O (2), Cu(pyim)(C5O5).2.5H(2)O (3), [Cu(H(2)bim)(C2O4)(H2O)].H2O (4) and [Cu(bpz)(C5O5)(H2O)] (5) [pyim = 2-(2-pyridyl)imidazole, H(2)bim = 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), H(2)bim (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.