Mixed-valence outer-sphere RuII/RuIII ion-pair complexes. Synthesis, experimental, and theoretical studies

Abstract

Two new ion-pair complexes, consisting of a cationic polypirydyl Ru(II) complex ([RuII(terpy)(bipy)Cl]+ or [RuII(terpy)(phen)Cl]+) and the cis-[RuIIICl2(pic)2]− anion (terpy = 2,2′:6′,2′′-terpyridine, bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline and pic− = picolinate) were synthesized. Magnetic and EPR studies were preceded by identifying the obtained species and checking the homogeneity and purity of the bulk material using various analytical techniques: single-crystal and powder X-ray diffraction, SEM, EDX, and FT-IR spectroscopies in the solid state, and ESI-MS in solution. The spectral characteristics in the UV–vis range and redox behavior of the ion-pair complexes were examined. The principal g components for [RuII(terpy)(bipy)Cl]+[cis-RuIIICl2(pic)2]−·(CH3)2CO·H2O, 1, and [RuII(terpy)(phen)Cl]+[cis-RuIIICl2(pic)2]−·2H2O, 2, and their RuIII precursor [H(Hpic)2]+[cis-RuIIICl2(pic)2]–∙2H2O were similar and typical for low-spin d5 species. The presence of one unpaired electron (in the dxy orbital) was shown by DFT calculations. The EPR spectra of 1 and 2 were characteristic for species in a singlet state (S = ½ systems) in contrast to that of their analog, previously reported for the first RuII/RuIII ion-pair complex, [RuII(bipy)2(pic)]+[cis-RuIIICl2(pic)2]−, typical for a species in the triplet state (S = 1 system).