Synthesis, molecular and electronic structures of a paramagnetic trimetallic cluster containing an unusual Mo3(l3-Se)2(l-Se)3 core

摘要

The electron precise [Mo3(l3-Se)(l-Se)3(dppe)3Br3]+ incomplete cuboidal complex, with six clusterskeletal electrons (CSE), was converted into the paramagnetic bicapped [Mo3(l3-Se)2(l-Se)3(dppe)3]+cluster (1+), with an unusual seven metal electron population, by treatment with elemental Ga. Thecluster core consists of an almost equilateral Mo3 triangle (Mo–Mo distances are in the range2.7583(7)–2.7748(7) Å with an average value of 2.77(3) Å), capped by two selenide ligands. The remainingselenium atoms bridge adjacent metal atoms, defining a virtually planar Mo3(l-Se)3 unit, with thecapping Se atoms positioned above and below this plane. The new complex possesses a doublet groundstate with the unpaired electron density delocalized over the three metal atoms. DFT calculations showthat the HOMO has ‘‘a1’’ symmetry, precluding any Jahn–Teller distortion on the cluster core and givingsupport to EPR and structural observations.