A CL-35 NQR STUDY ON CS-2[(AUCL2)-CL-I][(AUCL4)-CL-III]

A pair of Cl-35 NQR spin echo signals has been observed for the mixed valence complex Cs-2[(AuCl2)-Cl-I] [(AuCl4)-Cl-III] between 77 and 243 K. At 77 K, two resonance lines with the half widths Delta nu(Q) simi lar to 50 kHz were located at nu(Q1) = 17.28 MHz for the Au-I-Cl chlor ine and at nu(Q2) = 27.10 MHz for the Au-III-Cl chlorine in accordance with the crystal structure. The chlorine ionic characters of the Au-I -Cl and Au-III-Cl bonds are estimated as 0.63 and 0.42, respectively. The central gold atom carries a fractional protonic charge of 0.26 in [(AuCl2)-Cl-I](-) and 0.68 in [(AuCl4]-)-Cl-III. The charge distributi ons in the complex anions differ insignificantly from those in the iso lated [AuCl2](-) and [AuCl4](-) for ordinary complexes, indicating tha t the charge transfer interactions between the anions are weak in the mixed valence complex. The observed linear temperature dependencies of nu(Q) and log T-IQ are well explained by the lattice vibration. When the temperature was increased from 77 K, the resonance lines became gr adually weak without changing Delta nu(Q) and immeasurable above 215 K . ESR spectra taken at various temperatures revealed the presence of p aramagnetic sires of ca. 5 x 10(20) mol(-1) arising from Au(II). The s mall but finite concentration of Au(II) or some other reason should be responsible for the fade out phenomenon and the large Delta nu(Q) obs erved.