Interrelationships between the tetrahedral and planar polymorphs of bis(3-ethylamino-1-phenyl-but-2-en-1-ono)nickel(ii) and structural comparisons with related CoII, NiII, CuII, and ZnII complexes

Abstract

Conditions for the crystallization and interconversion of the green and brown polymorphs of bis(3-ethylamino-1-phenyl-but-2-en-1-ono)nickel(II) (Ni(B–Et)₂), which contain planar and tetrahedral complexes in accord with previous magnetic and spectroscopic studies, have been determined. Additionally, the series of β-diketoamine-containing complexes, M(B–Et)₂ and M(B–Bn)₂, (M = Co^II, Ni^II, Cu^II, Zn^II) obtained from condensation of benzoylacetone (B) with either ethylamine (Et) or benzylamine (Bn) followed by treatment with [MCl₄]²⁻ under basic conditions has been prepared and their structures characterized crystallographically. In contrast to Ni(B–Et)₂, Ni(B–Bn)₂ has been crystallized only in the planar form. M(B–Et)₂ and M(B–Bn)₂ (M = Co or Zn) have similar, nearly tetrahedral structures, while Cu(B–Et)₂ and Cu(B–Bn)₂ have structures that are decidedly intermediate between tetrahedral and planar. Despite the abilities of these complexes to exist in tetrahedral, planar, or intermediate structures in solution, it has not been possible to induce much structural variation in crystalline forms. While two polymorphs of Zn(B–Bn)₂ have been obtained, both have similar, tetrahedral structures. Only Ni(B–Et)₂ crystallizes in both planar and tetrahedral forms. None of the complexes formed cocrystals with fullerenes or solvates in which structural variation as seen in Ni(B–Et)₂ occurred.