Crown ether size effects, effective matrix isolation of metal halide, ligand conformation, and halogen bridging in cadmium halide–polyether adducts. A nuclear quadrupole resonance, infrared, and Raman study
Abstract
Adducts of composition mCdX2·polyether (X = Cl, Br, or I; m= 1, 1.5, 2, or 3) have been prepared with the polyethers CH3O[CH2CH2O]n–1CH3(n= 2–5) and the crown ethers [graphic omitted] (n= 5 and 6). I.r. and Raman spectra show that the polyethers chelate in the 1 : 1 adducts, but have different conformations for m≠ 1. The effects of CdX2 and HgX2 on the different C–O stretching and C–O–C bending modes are given. Metal–halogen stretching frequencies (from the Raman spectra) and halogen n.q.r. frequencies are reported, and assigned to bridging and terminal halogens. Analysis of these frequencies as a function of the number n of oxygen atoms in the polyether allows the frequencies of matrix-isolated Cdl2 and HgX2 to be estimated, and reveals anomalies in the n.q.r. spectra of CdX2·18-crown-6. These anomalies are explained in terms of the mismatch of the radii of the metal and the 18-crown-6 cavity.