Variations in the molecularity of bis(formylpyrrolyl)cobalt(II) complexes

Abstract

Abstract This work aims to extend the coordination chemistry of Co(II) with bis(2-formylpyrrolyl) ligands to different donor molecules. Treatment of a mixture of anhydrous CoCl2 and excess of pyridine in THF with two equivalents of sodium 2-formylpyrrolyl gives rise to complex [Co{κ2N,O-NC4H3-C(H) O}2(Py)2] (1) in good yields, after standard work-up procedures. By contrast, the reaction of two equivalents of sodium 2-formylpyrrolyl with anhydrous CoCl2 in neat THF or MeCN solutions systematically led, after standard work-up, to the identification of the tetrameric complex [Co{κ2N,O-NC4H3-C(H) O}2]4 (2) and other unknown contaminations. Analytically pure samples of complex 2 were only prepared when the synthesis reaction was performed in toluene at 90 °C. Complexes 1 and 2 are paramagnetic and were characterized by elemental analysis, magnetic susceptibility measurements (Evans method) and X-ray diffraction. Complex 1 is a hexacoordinated octahedral complex with a low-spin (S = 1/2) electronic configuration. On the other hand, the tetrameric complex 2 results from the self-assembling of the elusive and highly unsaturated complex “[Co{κ2N,O-NC4H3-C(H) O}2]” giving rise to a tetranuclear distorted cubane structure, comprising two hexacoordinated octahedral and two pentacoordinated trigonal bipyramidal Co(II) centers. Complex 2 revealed an overall high-spin (S = 3/2 per Co center) nature, as suggested in solution by the Evans method and in the solid state by SQUID magnetometry.