Designing ferromagnetism in Cu(II) complexes using an elusive near-orthogonal bridging mode of the pyrazole ring

Abstract The syntheses, crystal structures, magnetic properties and DFT calculations of four Cu(II) complexes of the formula [{Cu(2,2′-bpy)(HCPCA)}(H 2 O) 2 ]·3H 2 O ( 1 ), [Cu(dmbp)(HCPCA)] ( 2 ), [Cu(phen)(HCPCA)]·H 2 O ( 3 ) and [Cu(phen)(CPCA)] 2 ·DMF ( 4 ) [H 2 CPCA = 3-(3-carboxyphenyl)-1H-pyrazole-5-carboxylic acid, phen = 1,10-phenanthroline] are reported here. Our main focus was to design ta ferromagnetic complex and therefore concentrated on the mononuclear and binuclear copper complexes 3 and 4 . In complex 3 the pyrazole unit of the H 2 CPCA ligand binds (as HCPCA-) in a monodentate fashion to form the mononuclear complex, and in complex 4 the pyrazole unit of the H 2 CPCA ligand binds (as CPCA 2− ) in a bidentate fashion to form a binuclear complex, creating a near orthogonal orientation between the two Cu(II) ions. Temperature dependent magnetic susceptibility measurements show the appearance of weak ferromagnetic interactions for complex 4 , whereas complex 3 shows paramagnetic behavior. The results are in excellent agreement with theoretical Broken Symmetry-DFT calculations.