Mononuclear transition metal adamantane-1-carboxylates

Abstract

A procedure was developed for the synthesis of mononuclear first row transition metal coordination compounds with adamantane-1-carboxylate (AdCO₂), which allowed the synthesis of complexes NBu₄[M(AdCO₂)₃], where M^II = Mn, Ni, Co, Zn. The X-ray diffraction study showed that all AdCO₂ act as chelating ligands, which is the main distinguishing structural feature of the synthesized compounds. The formation of four-membered metallocycles leads to a small O—M—O angle (58.4–63.0°), resulting in the distorted trigonal-prismatic environment of the central atom in the coordination anions [M(AdCO₂)₃]⁻. Under similar conditions of the synthesis, Cu^II forms the complex (NBu₄)₂[Cu(AdCO₂)₂(SO₄)] existing in two differently colored modifications (green and light blue), which is due to a small difference in the environment of Cu^II in the solid state. Upon heating above 150°C, the light blue modification is transformed into the green modification. Using 1,3-diphenyltriazene (HL), it was demonstrated that the developed synthetic approach is applicable to the preparation of compounds, in which the coordination anions [ML₃]⁻ also contain only four-membered chelate metallocycles with the N—M—N angle tightened at the metal atom. The compounds NBu₄[ML₃], where M^II = Co and Ni, were isolated in individual state and were structurally characterized.