Variation of the exchange interaction in oximato-bridged Cu IIM II dimers (MCu, Ni, Mn). Crystal structure of [Cu(pdmg)Cu(bipy)(H 2O) 2] (ClO 4) 2· H 2O

Abstract

Three new dinuclear complexes of formula [Cu(pdmg)Cu(bipy)(H 2O) 2](ClO 4) 2·H 2O ( 1), [Cu(pdmg)Cu(terpy)]-(CIO 4) 2 ( 2) and [Cu(pdmg)Ni(cyclam)](ClO 4) 2·H 2O (3) (H 2pdmg=3,3′-aminopropylenedinitrilobis(2-butanoneoxime); bipy=2,2′-bipyridyl; terpy=2,2′:6′,2″-terpyridyl; cyclam=1,4,8,11-tetraazacyclotetradecane) have been synthesized. The structure of 1 has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P2 1/ a, with a=14.160(3), b=21.300(2), c=10.208(2) Å, β=95.44(2)°, V=3065(2) Å 3, Z=4, D x=1.68 g cm −3, μ(Mo Kα)=16.3 cm −1, F(000)=1584 and T=291 K. A total of 5263 reflections was measured over the range 1 ⩽θ⩽25°; of these, 2057 (independent and with I⩾2σ( I)) were used in the structural analysis. The final R and R w residuals were 0.062 and 0.064, respectively. The structure of 1 is made up of cationic [Cu(pdmg)Cu(bipy) 2(H 2O) 2] 2+ units, non-coordinated perchlorate anions and water of crystallization. The [Cu(pdmg)] fragment coordinates to the second copper(II) ion through its deprotonated oximate oxygens to afford a binuclear structure doubly bridged by the oximate groups in the cis arrangement. The Cu(NO) 2Cu bridging network is bent, the dihedral angle being 151°. The intramolecular metal-metal distance is 3.691(2) Å. The magnetic behavior of 1– 3 was investigated in the temperature range 50–300 K. The values of the exchange coupling constant J (the spin Hamiltonian being Ĥ=- JŜ A·Ŝ B) for 1– 3 were −674, −174 and −204 cm −1, respectively. The influence on the exchange coupling of the orientation of the magnetic orbitals and the number of unpaired electrons involved in the oximato-bridged Cu IIM II dimers (M=Cu, Ni, Mn) are analyzed and discussed.