A rational design for imidazolate-bridged linear trinuclear compounds frommononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): Syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)(2)Cu(hfac)(L)] (M = Zn-II, Cu-II, Mn-II)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate liga nd 2-[((imidazol-2-yhnethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](C lO4)(2). 2H(2)O (1) and [Cu(HL)Cl-2] (2), have been prepared and characteri zed. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pen tacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the dep rotonation of the imidazole moiety promotes a self-assembled process, by co ordination of the imidazolate nitrogen atom to a Cu-II center of an adjacen t unit, leading to the polynuclear complexes {[Cu(L)(H2O)](ClO4)}(n) (3) an d {[Cu(L)Cl]. 2H(2)O}, (4). Variable-temperature magnetic data are well rep roduced for one-dimensional infinite regular chain systems with J = -60.3 c m(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 i s used as a "ligand complex" for [M(hfac)(2)] (M = Cu-II, Ni-II, Mn-II, Zn- II) in a basic medium, only the imidazolate-bridged trinuclear complexes [C u(L)(hfac)M(hfac)(2)Cu(hfac)(L)] (M = Zn-II, Cu-II) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn-II as the central metal (7) can be prepared from the precursor [Cu(HL)Cl-2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with C-i symmetry, the center of symmetry being located at the central metal. T hus, the copper(II) fragments are in trans positions, leading to a linear c onformation. The magnetic susceptibility data (2-300 K), which reveal the o ccurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical threes-pin sys tems to give the coupling parameters J(CuCu) = -37.2 and J(CuMn) = -3.7 cm( -1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behavi ors are compared with those for analogous systems and discussed on the basi s of a localized-orbital model of exchange interactions.