화학공학소재연구정보센터
Inorganic Chemistry, Vol.56, No.21, 12764-12774, 2017
Ambient-Stable Bis-Azoaromatic-Centered Diradical [(L-center dot)M(L-center dot)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin-Spin Interaction
Bis-azoaromatic electron traps, viz. 2-(2-pyridylazo)azoarene 1, have been synthesized by colligating electron-deficient pyridine and azoarene moieties, and they act as apposite proradical templates for the formation of stable open-shell diradical complexes [(1(center dot-))Rh-III(1(center dot-))](+) ([2](+)), starting from the low-valent electron reservoir [Rh-I]. The less stable monoradical [Rh-III(1(center dot-))Cl-2(PPh3)(3)] (3) has also been isolated as a minor product. These p-radical complexes are multiredox systems, and the electron transfer processes occur exclusively within the pincer-type NNN ligand backbone 1. Molecular and electronic structures of the diradicals and monoradicals have been ascertained with the aid of X-ray diffraction, electrochemical, spectroelectrochemical, and spectral (electronic, IR, NMR, and EPR) studies. In the diradicals [2](+), the orthogonal disposition of two ligand pi orbitals linked via a closed-shell metal center (t(2)(6)) impedes significant coupling between the radicals. Indeed, the observed magnetic moment of [2a](+) lies near similar to 2.3 mu(B) over the temperature range 50-300 K. A very weak antiferromagnetic (AF) intramolecular spin-spin interaction between two ligand pi arrays in [(1(center dot-))Rh-III(1(center dot-))](+) have been found experimentally (J approximate to -5 cm(-1)), and this is further substantiated by density functional theory (DFT) calculations at the (U)B3LYP/6-31G(d,p) level.