STRUCTURE-ANALYSIS OF METAL(I) HALIDE MIXED-CRYSTALS BY MASNMR AND X-RAY-DIFFRACTION METHODS .2. CUBRXI1-X CRYSTAL

Mixed CuBrxI1-x crystals were prepared and analysed as complete solid solutions and core-shell type crystals by an X-ray diffraction method. Cu-63 MASNMR spectra in the complete solid solution were broad and appear to correspond to the overlapping peaks of five structural species: CuBr4, CuBr3I, CuBr2I2, CuBrI3 and CuI4. The CuBriI4-i (i = 0-4) species are believed to be composed of lattice sites of C1, C2v, C3v and T(d) symmetries. Signals in a core-shell type crystal, however, were sharp and obtained over a range of chemical shifts between solid Cul and CuBr. The NMR spectra were separated into several Gaussian peaks by curve fitting calculation with a nonlinear optimization method. The chemical shifts and half-widths in solid solution can be explained by considering components which involve second-order quadrupolar coupling tensors. Various values of quadrupolar coupling tensors are explicable by different tetrahedral symmetries of the CuBriI4-i species in the crystal.