Abstract
The bis-terdentate pyrazole-based ligand 3,5-bis{[N-(2-pyridylmethyl)amino]methyl}-1H-pyrazole (PMAPH) was synthesized from 3,5-(1H)-pyrazoledicarbaldehyde and 2 equiv of 2-(aminomethyl)pyridine, using sodium borohydride to reduce the imine intermediate. A family of dinuclear complexes [M-2(II/III)(PMAP)(2)](X)(2/4) was prepared by 2:2:2 reactions of MX2/PMAPH/base, where M = Zn-II and X = BF4-; M = Cu-II and X = ClO4-, BF4-, OAc-, NO3-; M = Ni-II, Fe-III and X = ClO4-, BF4-; M = Fe-II and X = SbF6-. Single crystal X-ray structure determinations on four complexes: [Fe-2(III)(PMAP)(2)](BF4)(2)center dot 2MeCN, [Ni-2(II)(PMAP)(2)](ClO4)(2)center dot 2MeCN, [Cu-2(II)(PMAP)(2)](BF4)(2)center dot 2MeCN, and [Zn-2(II)(PMAP)(2)](BF4)(2)center dot 2MeCN confirmed a dinuclear doubly pyrazolate-bridged structure for each. The two metal centers in these complexes have similar N-6 distorted octahedral coordination spheres, with all donors provided by the two deprotonated PMAP(-) ligands. Magnetic measurements reveal intra-dinuclear antiferromagnetic interactions for both the M = Cu-II and Ni-II [M-2(PMAP)(2)](BF4)(4) complexes, with J/k(B) = 252(2) K and J/k(B) = -24.7(2) K (H = -2JS(M)S(M)), respectively. Interestingly magnetic measurements show that the complex [Fe-2(II)(PMAP)(2)](SbF6)(2)center dot 2.25(C3H8O) is in a mixed high spin (HS)-low spin (LS) spin state, [HS-LS], from 300 to 1.8K, with no sign of spin crossover to a fully low spin form [LS-LS] even at 1.8 K.