Symmetry-Dependent Vibrational Circular Dichroism Enhancement in Co(II) Salicylaldiminato Complexes
Gennaro Pescitelli1, Steffen Lüdeke2, Marcin Górecki1,3
1Department of Chemistry and Industrial Chemistry , University of Pisa , Via Moruzzi 13 , 56126 Pisa , Italy.
Abstract:
Chiral coordination compounds of Co(II) and other open-shell metal complexes display enhanced vibrational circular dichroism (VCD) spectra associated with the existence of low-lying excited states (LLESs). In addition to the enhancement, a series of Co(II) salicylaldiminato complexes exhibits an almost monosignate pattern of VCD bands, a unique feature if compared with the usual alternation of positive and negative signals. Frequency and excited-state calculations reveal that VCD enhancement and sign reversal selectively affect the normal modes of B symmetry of the C2-symmetric pseudotetrahedral species thanks to their combination with one or more LLES having the same B symmetry. This proves the strict relation between VCD enhancement and monosignate appearance and demonstrates an unprecedented symmetry dependence of the two phenomena.
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