Co-existing pseudo-planar and saddle conformers of tetramethyl tetraaza[14]annulene platinum complexes: X-ray crystallographic studies on [PtII(tmtaa)] and trans-[PtIVCl2(tmtaa)]†

Abstract

Orange platelets of [Pt(tmtaa)], where H₂tmtaa = 6,8,15,17-tetramethyl-5,6,9,14,15,18-hexahydrodibenzo[b,i][l,4,8,11]tetraazacyclotetradecine, show the expected ‘pseudo-planar’ centrosymmetric macrocyclic conformation but red needles of another [Pt(tmtaa)] modification and purple trans-[PtCl₂(tmtaa)] both show saddle-form co-ordination with the metal ion only 0.046(1) Å (Pt²⁺) or 0.024(5) Å (Pt⁴⁺) above the N₄ plane; X-ray powder diffraction reveals similar dimorphism for [Pd(tmtaa)] but not for [Ni(tmtaa)].