Cyanide complexes of Ti(IV): A computational study

Density functional theory (B3LYP) and coupled-cluster techniques [CCSD(T)] including solvent effects have been used to study the homoleptic and mixed cyanide/isocyanide complexes of Ti(IV), $[Ti(CN)n]4−n$ $(n=1–6)$⁠. The most stable isomer is found to be the isocyanide form except for $n=6$ where the cyanide isomer is preferred. Calculations accounting for solvent effects show that, irrespective of the solvent employed, the hexacyanocomplex should be formed. We have additionally analyzed the bonding situation in these complexes in order to shed some light on the reasons for the predicted cyano-/isocyano preference. We have found that the more advantageous $σ$-bonding capabilities of the cyanide form become increasingly important for larger n eventually favoring the cyanoisomer for $n=6$⁠. We finally compare the bonding situation in hexacyanotitanate(IV) with that of hexacyanoferrate(II).