The metal NMR spectra of thiolate and phenylselenolate complexes of zinc(II) and mercury(II)

Abstract

Soluble thiolato-zincates and -mercurates(II) of the general type M(SR) 2− 4 and the phenylselenolato complexes M(SePh) 2− 4 (M = Zn or Hg) have been prepared in situ from the appropriate metal nitrate and excess thiolate or selenolate. The high field metal NMR spectra of these complexes have been measured, at 25.0 and 71.5 MHz for 67Zn and 199Hg respectively, with isotopic enrichment to 89.7 atom% for 67Zn, but at natural abundance for 199Hg. The zinc complexes studied in D 2O solution, were Zn(SR) 2− 4 (R = Me, Pr i, or Ph), Zn??? S S]) 2 2 and Zn(SePh) 2− 4. The variation of δ Zn with ligand was found to be −SePh < −SPh < −Spr i < −SMe š −S(CH 2) 2S −, as has been found earlier for 113Cd also; the shifts for solutions in which [Zn] total = 0.15 M, to higher frequency than the resonance of 2m Zn(ClO 4) 2 at 297 K range from 224 to 418 ppm, and the approximate linewidths from ca. 55 Hz for Zn(SMe) 2− 4 at 368 K to ca. 1200 Hz for Zn(SPr i) 2− 4 at 297 K or Zn??? S S]) 2− 2 at 363 K. The line widths appear to be the major factor limiting the application of 67Zn NMR towards complexes of less symmetrical thiolates; rapid chemical exchange is not a problem, as 1H and 13C NMR studies of the zinc complexes show them to be less labile than their cadmium analogs. Conversely the mercury complexes studied here ▪ ▪(R = H, Me, Et, or CH 2OH), Hg(SR) 4 (R = M=, Et, Pr i, or Ph) and Hg(SePh) 2− 4) are more labile than their cadmium counterparts, and this lability reduces the utility of 199Hg NMR in cases where multiple mercury-binding sites are available. The overall variation of δ Hg with ligand , −SePh < −SPh < −SR (R = alkayl) < chelating vicinal dithiolates, is the same as found in the metal NMR of the corresponding zinc and cadmium complexes, but the (relatively small) effects of alkyl substitution are dissimilar. For ca. 0.1 M solutions in 1:1 (ν:ν) H 2O: D 2O at 297 K, the 199Hg chemical shifts to higher frequency than the signal of 0.1 M Hg(ClO 4) 2 in 5% (ν:ν) HClO 4 range from 1275 ppm in Hg(SePh) 2− 4 to 2234 ppm for ▪ the linewidths are relatively sharp ( e.g. ???4 Hz for Hg(SMe) 2− 4, ???75 Hz for Hg(SPh) 2− 4).