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, ¹J_13C-15N = 8 Hz, ¹J_13C-125Te = 748 Hz, ²J_15N-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]^•.