Structure and bonding energy calculations of nitrosyl, thionitrosyl and selenonitrosyl complexes [(PNP)Ir(NX)]+ (X = O, S, Se): A DFT study

Abstract

Structure and bonding analyses of the complexes [(PNP)Ir(NX)]+ (X=O, S, Se; PNP=N(CHCHPMe2)2) were investigated at the DFT, DFT-D3 and DFT-D3(BJ) levels using BP86, BLYP, PBE, revPBE and TPSS functionals. The Ir–NX bond in the thionitrosyl complex is longer than that in the nitrosyl and selenonitrosyl complexes, which is consistent with the observed trend for their experimental values. The Ir–NX bond has essentially IrNX double bond character, which supports the σ-donor and π-acceptor abilities of the [NX]+ ligands. The non-covalent P–NX distances decrease in the order DFT>DFT-D3>DFT-D3(BJ). The Ir–NX bond has a larger covalent character (85.7, 75.9 and 74.6%). Dispersion interactions between the metal and [NX]+ fragments are in the range 3.2–5.5kcal/mol (BP86), 3.2–5.4kcal/mol (BLYP), 1.9–3.1kcal/mol (PBE), 3.5–5.5kcal/mol (revPBE) and 2.6–3.8kcal/mol (TPSS), which are smaller than the corresponding DFT-D3(BJ) dispersion corrections 4.9–8.6kcal/mol (BP86), 5.2–7.9kcal/mol (BLYP), 2.7–4.0kcal/mol (PBE), 5.3–7.6kcal/mol (revPBE) and 2.7–5.2kcal/mol (TPSS). The dispersion corrected DFT (DFT-D3 and DFT-D3(BJ)) methods provide quite an accurate estimate of the dispersion energy, which can be judged by the observation that the experimental and optimized Ir–NX bond distances are consistent with the most accurate dispersion corrected DFT-D3(BJ) bond dissociation energy of Ir–NX bonds.