Formation and Structure of Gas-Phase Lanthanide(III) Cyanobenzyne Complex (²-4-CNC₆H₃)LnCl₂ ^-, Obtained via Both the Single- and Dual-Ligand Strategies

The lanthanide(III) cyanobenzyne complexes (eta(2)-4-CNC6H3)LnCl(2)(-) (Ln = La-Lu except Eu; Pm was not examined) were generated in the gas phase using an electrospray ionization mass spectrometry coupled with collision-induced dissociation (CID) technique. For all lanthanides except Sm, Eu, and Yb, (4-CNC6H3)LnCl(2)(-) can be generated either via a single-ligand strategy through consecutive CO2 and HCl losses of (4-CNC6H4CO2)LnCl(3)(-) or via a dual-ligand strategy through successive CO2/C6H5CN or 4-CNC6H4CO2H and CO2 losses of (4-CNC6H4CO2)(2)LnCl(2)(-). For Sm and Yb, although only reduction products LnCl(3)(-) were formed upon CID of (4-CNC6H4CO2)LnCl(3)(-), (4-CNC6H3)LnCl(2)(-) were obtained via the dual-ligand strategy without the appearances of other products. CID of (4-CNC6H4CO2)EuCl3- and (4-CNC6H4CO2)(2)EuCl2- gave EuCl3- and the cyanophenyl complex (4-CNC6H4)EuCl2-, respectively, in both of which the +III oxidation state of Eu was reduced to +II. Density functional theory (DFT) calculations reveal that (4-CNC6H3)LnCl(2)(-) are formally described as Ln(III) cyanobenzyne complexes, (eta(2)-4-CNC6H3)LnCl(2)(-), with the dianionic cyanobenzyne ligand (4-CNC6H32-) coordinating to the Ln(III) centers through two Ln-C sigma bonds, which is in accordance with their reactivities toward water. Benzyne and substituted benzyne complexes (XC6H3)LuCl2- (X = H, 3-CN, 4-F, 4-Cl, and 4-CH3) were also synthesized in the gas phase via the single- and dual-ligand strategies.