Spectroscopic, structural and DFT study of the responses of carbonylmetal crown ether complexes to alkali metal cations
Stephenson, G. Richard
Anson, Christopher E
; Creaser, Colin S
; Daul, Claude A
FTIR spectra of tricarbonyl(η⁶-benzo-15-crown-5)chromium(0) (1) in the presence of lithium, sodium and potassium perchlorate salts in methanol show different responses in the Cr–CO vibrational region of the spectrum. Data from the symmetric (νsym) and antisymmetric (νasym) Cr–CO vibrational stretching modes have been analysed by principal component analysis (PCA) to generate a factor score plot that provides a visual representation of these differential responses. X-ray crystallographic data for the sodium perchlorate complex 1·Na⁺ and dimensions from DFT-derived structures of 1·Li⁺, 1·Na⁺ and 1·K⁺ 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 with a more compact O(4)–C(9)–C(4)–O(8), while Na⁺ and K⁺ differ crucially in the extent of σ and π contributions to their effect on νsym and νasym. A comparison of the FTIR data from 1, tricarbonyl(η⁶-1-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) values [calculated from ΔR(cation)] distinguished different effects in the FTIR spectra of 1 and 3 for different pairs of cations.
European Journal of Inorganic Chemistry. - 2011///2086–2097
European Journal of Inorganic Chemistry