Interaction between heterobinuclear molecules and nature of the ground spin state in oximato-bridged [CuIIMII]2 bis-binuclear complexes (M = Cu, Ni, Mn):: crystal structure of [Cu(pdmg)Ni(Me3[12]N3)(EtOH)](ClO4)2

Two new heterobimetallic complexes [Cu(pdmg)Ni(Me-3[12]N-3)(CH3CH2OH)](ClO4)(2)(2) and [Cu(pdmg) Mn(bipy)(2)]-ClO4)(2) . H2O (3) (H(2)pdmg = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2 10-dione dioxime; Me-3[12]N-3 = 2,4,4-trimethyl-1,5,9-triazacyclododeca-1-ene; bipy = 2,2'-bipyridyl) have been prepared and characterized. The structure of 2 has been determined by single-crystal X-ray diffraction methods. It consists of [Cu(pdmg)Ni(Me-3[12]N-3)(CH3CH2OH)](2+) cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH3CH2OH)] complex coordinates to the [Ni(Me-3[12]N-3)](2+) fragment to afford the binuclear unit doubly-bridged by oximato groups in cis arrangement. The coordination geometry around the copper atom is square-pyramidal, whereas the nickel atom exhibits a trigonal-bipyramidal surrounding The intramolecular Cu-Ni distance is 3.810(6) Angstrom. In the crystal, two [(CuNII)-N-II] dimeric units are related through an inversion center, giving rise to a bis-binuclear entity with a relatively short intermolecular Cu-Cu separation of 4.175(6) Angstrom. Variable-temperature magnetic susceptibility measurements (2.0-300 K) for 2 correspond to an almost isolated Cu(II)Ni(Ir) pair with an intrapair interaction parameter J= -143.6(2) cm(-1). However, the EPR spectrum at 4.2 K is that of a triplet spin state arising from the interaction between the two doublet spin states within the [(CuNiII)-Ni-II](2) bis-binuclear entity. The magnetic properties of 3 unambiguously reveal the bis-binuclear nature of this compound, as is the case for the related homometallic complex [Cu(pdmg)Cu(bipy)(H2O)(2)](ClO4)(2). H2O (1). The intra- (J) and interpair (j) interaction parameters for 3, as deduced from the analysis of its magnetic susceptibility data in the temperature range 2.0-300 K, are - 50.9(2) and 1.50(2) cm(-1), respectively. The field dependence of the magnetization of 3 at 2.0 K corresponds to that of a nonet state arising from the interaction between two quintuplet spin states within the [(CuMnII)-Mn-II](2) bis-binuclear entity. The interaction between the heterobinuclear Cu(II)Mn(II) molecules and its influence on the nature of the ground spin state for 3 are analyzed and discussed in the framework of a spin polarization scheme. (C) 1999 Elsevier Science S.A. All rights reserved.