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.