Binuclear copper(II) complexes of new dinucleating ligands with a pyrazolate group as an endogenous bridge. Effects of exogenous azide and acetate bridges on magnetic properties

Abstract

New dinucleating ligands containing pyrazole as an endogenous bridging group, 3,5-bis-[N-(2-pyridylmethyl)carbamoyl] pyrazole (H₃L¹), 3,5-bis{N-[2-(diethylamino)ethyl]carbamoyl}pyrazole (H₃L²), and 3,5-bis{N-[3-(dimethylamino)propyl]carbamoyl}pyrazole (H₃L³), and their binuclear copper(II) complexes with azide or acetate ion as an exogenous bridge, [CU₂L(N₃)(H₂O)₂]·H₂O(L = L¹–L³) and [Cu₂L¹(O₂CMe)]·2MeOH, have been obtained. Cryomagnetic investigations (5–300 K) reveal a significant antiferromagnetic spin exchange for the azide-bridged complexes(–J= 371–297 cm^–1), but a ferromagnetic spin exchange (J > +8.9 cm^–1) for the acetate-bridged complex. The azide-bridged complexes are e.s.r. silent. The acetate-bridged complex is unstable in dimethylformamide (dmf) but a quickly prepared dmf frozen solution of the sample gives X-band signals characteristic of a spin-triplet (S= 1) state, together with signals due to a spin doublet(S=½) attributable to monomeric copper(II). Signals at 812, 1 292, and 4 380 G show a seven-line hyperfine structure (A_zz= 0.0103 cm^–1); the first and third signals are assigned to ΔM_s= 1 transitions and the second to the ΔM_s= 2 transition of the parallel resonance of the spin-triplet state. E.s.r. simulation based on the spin Hamiltonian for the spin triplet of a dicopper(II) system gives g_zz= 2.533, D= 0.210 cm^–1, and E= 0.020 cm^–1. Only two components of the perpendicular resonances are recognizable at 2 113 and 3 812 G which give g_x= 2.055.