{μ-Bis(diphenylphosphino)methane}(1-alkyl-2-(arylazo)imidazole) copper(I) perchlorate: Synthesis, structure and photochromism

Abstract

1-Alkyl-2-(arylazo)imidazole (RaaiR/), a bidentate N(azo), N(imidazolyl) chelator, and bis(diphenylphosphino)methane (dppm), a P, P bridger, have been used to prepare phosphino bridged dinuclear-Cu(I) complexes, [Cu(μ-dppm)(RaaiR/)]2(ClO4)2. The structures of the complexes have been established by spectral (UV–Vis, IR, 1H NMR) data and the confirmation has been done in case of [Cu(μ-dppm)(HaaiEt)]2(ClO4)2 by single crystal X-ray diffraction studies. Optical stimulation using UV light (365 nm) in methanol solution of the complexes shows that the coordinated RaaiR/ undergoes trans-to-cis isomerization about NNAr. The rate of trans-to-cis isomerization varies 1.11 × 10−8−1.89 × 10−8 s−1 and is largely dependent on mass of the photochrome and strain/steric crowding generated about NN bond. Quantum yields (ϕt→c) of trans-to-cis isomerization, 0.0843–0.1421, are calculated and free ligand shows higher ϕ (0.17–0.26) than their complex phase. The cis-to-trans isomerisation is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerisation is calculated by controlled temperature experiment and is found that Ea (ligands) > Ea (complexes).