Fine tuning of pentachromium(ii) metal string complexes through elaborate design of ligand

Abstract

New pentachromoium metal string complexes [Cr₅(μ₅-L)₄X₂] (X = Cl⁻, L = dppzda²⁻ (1), dpzpda²⁻ (2); X = NCS⁻, L = dppzda²⁻ (3), dpzpda²⁻ (4)) were designed and synthesized through pyrazine-modulation of tripyridyldiamine ligand. X-Ray crystallographic studies revealed a linear metal chain structure consisting of two quadruple Cr–Cr bonds and a separated high spin Cr(II) at an end in crystallized form. A quintet ground state was observed for all pentachromium(II) molecules by magnetic study with g values of 2.04–2.18. While the electronic structure remained unchanged after the modification of ligands, electrochemistry showed a significant change in the molecular orbital energy levels of metal string molecules. Observation of the first oxidation peak of 1 at +0.57 V and of 2 at +0.73 V revealed that these complexes are quite resistant to oxidation. Single molecular conductance measurements showed that the complex exhibited good electronic conductance.