Synthesis, crystal structure and magnetic properties of [Co(bpcam)2]ClO4·dmso·H2O, [Co(bpcam)2]2[Co(NCS)4]·dmso·H2O and [Ni(bpcam)2]·H2O [Hbpcam = bis(2-pyrimidylcarbonyl)amide]

Abstract

The preparation, spectroscopic characterization, structural study and magnetic investigation of three new complexes of formula [Co(bpcam)₂]ClO₄·dmso·H₂O (1), [Co(bpcam)₂]₂[Co(NCS)₄]·dmso·H₂O (2) and [Ni(bpcam)₂]·H₂O (3) [Hbpcam = bis(2-pyrimidylcarbonyl)amide] are reported. Each bpcam group in 1–3 acts as a tridentate ligand being coordinated to the cobalt(III) (1 and 2)/nickel(II) (3) ions through three nitrogen atoms in a mer-arrangement. Six-coordinate cobalt(III) and nickel(II) occur in 1 and 3 respectively, whereas six-coordinate cobalt(III) and four-coordinate cobalt(II) coexist in 2. Cyclic voltammetry of 1 in acetonitrile shows the occurrence of one quasi reversible Co^III ↔ Co^II process. Direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 2 and 3 were carried out in the temperature range 1.9–295 K. The magnetic behaviour of 2 obeys to the zero-field splitting effects (D_Co) of the ⁴A₂ ground term of the pseudotetrahedral [Co(NCS)₄]²⁻ complex anion. A Curie law for a magnetically isolated nickel(II) ion in the high temperatures domain occurs for 3, the small decrease of χ_MT below 10 K being due zero-field splitting effects. The analysis of the magnetic susceptibility data of 2 and 3 through the spin Hamiltonian H = D_M[S_z² − S(S + 1)/3] + g_MβHS [M = Co(2) and Ni(3)] led to the following set of values: g_M = 2.37 (2) and 2.12 (3) and |D_M| = 34.7 (2) and 1.72 cm⁻¹ (3).