BR-81 NQR FOR UNCOORDINATED BR- IONS IN TRANS-[COBR2(EN)2] [H5O2]BR2 AND TRANS-[COBR2(EN)2] [D5O2]BR2

The temperature dependence of the Br-81 NQR frequencies (nu(D)) for un coordinated Br- ions in trans-[CoBr2(en)2] [D5O2)Br2 (D) has been dete rmined by a continuous-wave spectrometer. nu(D) amounted to 16.200 MHz at 273 K. This is lower by 418 kHz than the Br-81 NQR frequency (nu(H )) for trans-[CoBr2(en2] [H5O2]Br2 (H). The frequency difference (DELT A(nu) = nu(H) - nu(D)) remained almost constant in the temperature ran ge studied. A shortening of the O - H bond length caused by deuteratio n could explain the magnitude and the sign of DELTAnu on the basis of a point charge model calculation. The compounds D and H yielded Br-81 NQR lines in the range 110-320 K and 90-343 K, respectively. As to the Co-59 NQR frequencies nu1 (7/2-5/2), the observed isotope frequency s hifts (DELTAnu1 = nu1H-nu1) between D and H were smaller than 5 kHz. B elow 160 K, Co-59 resonances were only available by pulsed experiments . Co-59 NQR spin-lattice relaxation times T1Q of 0.54 ms at 194 K and 4.8 s at 77 K for H have been observed.