Trans-Influence-Driven Coordination Plasticity in Carbazolide NNN Pincer Nickel(II) Complexes.

Carbazolide-based NNN pincer ligands impart a strong electronic trans influence at nickel(II) centers, leading to unusual coordination behavior. A series of Ni(II) complexes supported by CztBu(PyrH)2- reveals pronounced coordination plasticity depending on the ancillary ligand and solvent environment. Halide complexes preferentially form solvated octahedral species in coordinating media and exhibit partial ionization of the Ni-X bond, as supported by salt-metathesis experiments and ionic conductivity measurements. Oxygen-donor ligands promote μ-alkoxide dimer formation with temperature-dependent solution dynamics, while strongly donating ligands such as CF3- and N(SiMe3)2- stabilize classical square-planar geometries. The fluoride complex displays solvent-dependent speciation, with hydrogen-bonding interactions in CHCl3 stabilizing a monomeric square-planar structure. Comparison with diphenylamide analogues confirms that the rigid and strongly donating carbazolide backbone is responsible for this behavior. These results demonstrate how backbone electronics can modulate Ni-ligand lability and coordination geometry in pincer complexes.