Steric effects and excited-state geometry. the resonance Raman spectroscopy of [Ru2X3(tacn)2]2+ (X=Cl, Br and I) and [Ru2X3(Me3tacn)2]2+ (X=Cl, Br or I)

Abstract

The mixed-valence complexes [L3RuII1/2X3RuII1/2L3]2+, where X=halide and L=amine, commonly referred to as the ‘ruthenium blues,’ all exhibit a strong absorption band which dominates the visible region of their electronic spectra. The resonance Raman (RR) spectra of [Ru2X3(tacn)2]2+ (tacn=1,4,7-triazacyclononane, X=Cl, Br or I) and [Ru2X3(Me3tacn)2)]2+ (Me3tacn=1,4,7-trimethyl-1,4,7-triazacyclononane, X=Cl or Br) were recorded at room and liquid helium temperatures using excitation wavelengths which fall within the contour of the main visible absorption bands. Unlike their ammine analogues, [Ru2X3(NH3)6]2+(X=Cl or Br), whose RR spectra contain only a few bands which are relatively straightforward to assign, the RR spectra of some of the tacn and Me3tacn complexes are spectacular, exhibiting long progressions involving a number of different combination bands. This paper presents the detailed assignments of RR spectra of the above complexes. Analysis of the low-temperature RR spectra yielded qualitative information about the geometry changes of the complexes upon electronic excitation. © 1998 John Wiley & Sons, Ltd.