A Thorough Characterization of the Tellurocyanate Anion

Tellurocyanate anions, [TeCN]−, are the heaviest group 16 congeners 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 of 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 labelled [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 induced heavy-atom effect on the light-atom shielding (SO-HALA-effect). In contrast 15N shifts are well described also without considering relativistic effects and/or SOC. Here, the electronic situation of the C–N bond within [ChCN]− causes Ch-dependent differences in the shift-dominating scalar part of the magnetic response density.