A Thorough Characterization of the Tellurocyanate Anion.

Tellurocyanate, [TeCN]-, is the heaviest group 16 congener of the cyanate anion, [OCN]-. Due to the relative instability of the C─Te bond, tellurocyanate chemistry has seen only scarce attention. Here, we present the facile synthesis and thorough characterization of [K@crypt-222][TeCN]. The anion is essentially linear with interatomic distances C─N = 1.150(6)Å and C─Te = 2.051(4)Å, thus approximating a C≡N triple bond and for C─Te a bond order between 1 and 2. Fully 13C and 15N labeled [Te13C15N]- allowed for the extraction of chemical shifts and all possible coupling constants (13C = 77.8 ppm, 15N = 285.7 ppm, 125Te = -566 ppm, 1J13C-15N = 8 Hz, 1J13C-125Te = 748 Hz, 2J15N-125Te = 55 Hz), which were also determined independently by quantum chemical calculations. In the series [ChCN]- (Ch = O─Te), [TeCN]- shows the strongest spin-orbit coupling (SOC) induced heavy-atom effect on the light-atom shielding (SO-HALA-effect). In contrast, 15N shifts are also well described without considering relativistic effects and/or SOC. Negative-ion photoelectron spectroscopy was used to extract the electron affinity (EA = 3.034 eV) and spin-orbit splitting (3807 cm-1) of [TeCN]•. These values continue the trends of falling EA and rising SOC in the series [ChCN]•.