Publication

Journal	Chemistry, An european journal
Title of proceedings	Chemistry, An european journal
DOI	10.1002/chem.200

Principal component analysis (PCA) of FTIR spectra in the presence of lithium, sodium and potassium perchlorate salts in methanol differentiates the responses of tricarbonyl(η6-benzo-15-crown-5)- chromium(0) (1), using data from the symmetric (νsym) and antisymmetric (νasym) Cr-CO vibrational stretching modes. X-ray crystallographic data for the sodium perchlorate coordination complex 1٠۰Na+ and dimensions from DFT-derived structures of 1٠۰Li+, 1٠۰Na+ and 1٠۰K+ indicate that binding M+ in the crown causes electron density and structural changes in the [O(4)-C(9)- C(4)-O(8)]Cr-C(1)=O(1) sections of 1, which vary depending on the nature of the cation. This suggests a mode of action in which Li+ associates less strongly with O(4/8) than with the oxygen atoms at the far end of the crown, while Na+ and K+ differ in the extent of σ and π contributions to their effect on νsym and νasym. Comparing FTIR data6 from complex 1, tricarbonyl(η -1-phenyl-1-aza-15- crown-5)chromium(0) (2) and tricarbonyl(η6-2-phenyl-15-crown-5)- chromium(0) (3) with a wider range of cations (NH4+, Li+, Na+, K+, Rb+, Cs+,Mg2+, Ba2+) and anions (AcO–, BPh4–, Br–, C1O4–, I–, SCN–), showed that 1 and 3 both responded significantly to the different metal cations, but 2 did not. The relative cation differentiation of 1, 2 and 3 was measured using the parameter ΔR(cation), and ratios of ΔN(cation)s [calculated from ΔR(cation) values] distinguished different effects in the FTIR spectra of 1 and 3 for different pairs of cations.