Spectroscopic, Structural and DFT Study of the Responses of Carbonylmetal Crown Ether Complexes to Alkali Metal Cations

FTIR spectra of tricarbonyl(η 6 ‐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 (ν sym ) and antisymmetric (ν asym ) 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 ν sym and ν asym . A comparison of the FTIR data from 1 , tricarbonyl(η 6 ‐1‐phenyl‐1‐aza‐15‐crown‐5)chromium(0) ( 2 ) and tricarbonyl(η 6 ‐2‐phenyl‐15‐crown‐5)chromium(0) ( 3 ) with a wider range of cations (NH 4 + , Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ba 2+ ) and anions (AcO – , BPh 4 – , Br – , C1O 4 – , 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 Δ R(cation) , and ratios of Δ N(cation) values [calculated from Δ R(cation) ] distinguished different effects in the FTIR spectra of 1 and 3 for different pairs of cations.