Steric effects on the electronic and molecular structures of nickel(II) and cobalt(II) 2,6-dipyrazol-1-ylpyridine complexes

The complexes [M((LR)-R-1)(2)](BF4)(2) (M=Ni, Co; (LR)-R-1 = 2,6-dipyrazol- 1-ylpyridine [(LH)-H-1], 2,6-bis-{3-iso-propylpyrazol-1-yl}pyridine [(LPri) -Pr-1], 2,6-bis-{3-phenylpyrazol-1-yl}pyridine [(LPh)-Ph-1], 2,6-bis-{3-[2, 4,6-trimethylphenyl]pyrazol-1-yl}pyridine [L(1)Mes]) and [M(L-2)(2)](BF4)(2 ) (M = Ni, Co; L-2 = 2-{3-[2,4,6-trimethylphenyl]pyrazol-1-yl}-6-{5-[2,4,6- trimethylphenyl]pyrazol-1-yl}pyridine) have been prepared. Single crystal s tructure determinations of [M((LH)-H-1)(2)](BF4)(2) (M = Ni, Co) and solvat es of [Ni((LMeS)-Me-1)(2)](BF4)(2), [Co(L(1)Mes)(2)](ClO4)(2) and [Co(L-2)( 2)](BF4)(2) all show six-coordinate metal centres with local near-D-2d symm etry. The L(1)Mes and L-2 mesityl substituents have only a small effect on the M-N{pyrazole} (M = Ni, Cc) bond lengths in these compounds. The d-d spe ctra of the complexes show that L(1)Mes is a significantly better donor lig and than (LH)-H-1, (LPi)-P-1 or (LPh)-Ph-1, and that (LPri)-Pr-1 is a weake r ligand than might be expected purely on inductive grounds. A combination of UV-Vis/NIR, EPR, NMR and magnetic measurements have demonstrated that al l the Co(II) compounds are high-spin in the solid state and in solution at 290 K. (C) 2001 Elsevier Science Ltd. All rights reserved.