Chemistry at the apical position of square-pyramidal copper(II) complexes: synthesis, crystal structures, and magnetic properties of mononuclear Cu(II), and heteronuclear Cu(II)–Hg(II) and Cu(II)–Co(II) complexes containing [Cu(AA)(BB)] + moieties (AA=acetylacetonate, salicylaldehydate; BB=1,10-phenanthroline, Me 2bipy=4,4 ′-dimethyl-2,2 ′-bipyridine)

Abstract

New families of mononuclear and heteropolynuclear complexes have been obtained by using [Cu(AA)(BB)] + building-blocks (AA=acetylacetonate or salicylaldehydate; BB=1,10-phenanthroline, 4,4 ′-dimethyl-2,2 ′-bipyridine). The following mononuclear complexes have been structurally characterized: [Cu(acac)(Me 2bipy)]ClO 4 ( 1), [Cu(acac)(Me 2bipy)(NCS)] ( 2), [Cu(acac)(phen)(NCS)] ( 3). In compound 1 the copper(II) exhibits a square planar geometry, while the stereochemistry of compounds 2 and 3 is square pyramidal, with the isothiocyanato ligand coordinated in the apical position. The reaction between 2 and HgCl 2 affords a trinuclear complex, [{Cu(acac)(Me 2bipy)(μ-NCS)} 2Hg(SCN) 2] ( 4). The reaction between 3 and HgCl 2 leads to tetranuclear Cu 2Hg 2 compound, [{Cu(acac)(phen)(NCS)} 2{(ClHg) 2(NCS) 2}] ( 5), with a unique structure, and to a trinuclear complex, [{Cu(acac)(phen)(NCS)} 2Hg(SCN) 2] ( 6). The structure of 5 consists of a {Hg 2(NCS) 2} ring on which two [Cu(acac)(phen)(NCS)] moieties are attached. In compounds 4, 5 and 6 the mercury atoms are tetracoordinated. By reacting [Cu(sal)(phen)(OClO 3)] with (NEt 4) 2[Co(NCS) 4], a heterohexanuclear compound is obtained: [{Cu(sal)(phen)(SCN)} 2Co(NCS) 2] 2 ( 7), with the following topology of the metallic centers: Cu–Co–Cu–Cu–Co–Cu. The cobalt(II) ions in 7 are tetracoordinated by nitrogen atoms arising from two bridging and two terminal thiocyanato ligands. The central copper(II) ions are bridged by the phenoxo oxygen atom arising from the sal − ligand. The cryomagnetic properties of compounds 2– 5 and 7 have been investigated and discussed. The magnetic behavior of compounds 2– 5 has been ascribed to intermolecular exchange interactions mediated by the stacking interactions. The magnetic interaction between Cu(II) and Co(II) in 7 was found ferromagnetic ( J=+0.6 cm −1), as theoretically predicted. The exchange interactions between the central copper(II) ions is antiferromagnetic ( J=−5.8 cm −1).