Controlling metal-ligand-metal oxidation state combinations by ancillary ligand (L) variation in the redox systems [L2Ru(mu-boptz)RuL2](n), boptz=3,6-bis(2-oxidophenyl)-1,2,4,5-tetrazine, and L = acetylacetonate, 2,2 '-bipyridine, or 2-phenylazopyridine

Abstract

The new compounds [(acac)(2)Ru(mu-boptz) Ru(acac)(2)] (1) [(bpy)(2)Ru(mu-boptz)Ru(bpy)(2)] (ClO4)(2) (2-(ClO4)(2)), and [(pap)(2)Ru(mu-boptz)Ru(pap)(2)](ClO4)(2) (3-(ClO4)(2)) were obtained from 3,6-bis(2-hydroxyphenyl)1,2,4,5-tetrazine (H(2)boptz), the crystal structure analysis of which is reported. Compound I contains two antiferromagnetically coupled (J=-36.7cm(-1)) Ru-III centers. We have investigated the role of both the donor and acceptor functions containing the boptz(2-) bridging ligand in combination with the electronically different ancillary ligands (donating acac(-), moderately it-accepting bpy, and strongly pi-accepting pap; acac=acetylacetonate, bpy-2,2'-bipyridine pap =2-phenylazopyridine) by using cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance (EPR) spectroscopy for several in situ accessible redox states. We found that metal-ligand-metal oxidation state combinations remain invariant to ancillary ligand change in some instances; however, three isoelectronic paramagnetic cores Ru( mu-boptz)Ru showed remarkable differences. The excellent tolerance of the bpy co-ligand for both Ru-III and Ru-II is demonstrated by the adoption of the mixed-valent form in [L2Ru( mu-boptz)RuL2](3+), L=bpy, whereas the corresponding system with pap stabilizes the Ru-II states to yield a phenoxyl radical ligand and the compound with L= acac(-) contains two Ru-III centers connected by a tetrazine radical-anion bridge.