Nature of Cr—Cr “quadruple bond”. Photoelectron spectra of solid tetra-µ-acetatodichromium(II), solid and gaseous tetra-µ-trifluoroacetate-dichromium(II), and gaseous tetra-µ-{6-methyl-2-hydroxypyridine}-dichromium(II) and -dimolybdenum(II)

Abstract

Photoelectron spectral data are reported for solid Cr₂(O₂CMe)₄, solid and gaseous Cr₂(O₂CCF₃)₄ and gaseous Cr₂(MHP)₄ and Mo₂(MHP)₄(H{MHP}= 6-methyl-2-hydroxypyridine). For Cr₂(O₂CR)₄(R = Me or CF₃) the metals' valence electron ionizations are all contained within one broad low energy band, whereas for Cr₂(MHP)₄ and Mo₂(MHP)₄ the metal–metal bonding orbitals have ionization energies δ < π, σ. There is found to be a close correlation between bond length and quadruple bond character of the Cr—Cr bond. The assignment of the metal ionizations in Cr₂(O₂CR)₄ is facilitated by the comparison between solid and gas phase spectra.