Molecular structure and bonding in octamethylporphyrin tin(ii), SnN sub(4)C sub(28)H sub(28 )

Gas-phase electron diffraction was applied for the molecular structure determination of octamethylporphyrin tin(ii), SnN sub(4)C sub(28)H sub(28 ), at the temperature of 706(10) K. The molecule was found to possess C sub(4v) symmetry with the Sn atom 1.025(30) Aa above the plane of the N atoms and the following main internuclear distances (r sub(h1), Aa): Sn-N = 2.301(9), C sub( alpha )-N = 1.360(8), C sub( alpha )-C sub( beta ) = 1.453(4), C sub( alpha )-C sub(m) = 1.395(4), C sub( beta )-C sub(CH3) = 1.498(4). Quantum chemical calculations, DFT (B3LYP, BP86, PBE, PBE0) with cc-pVDZ, cc-pVTZ and cc-pVQZ basis sets reproduce the experimental bond distances with accuracy within 0.03 Aa. According to NBO(B3LYP/cc-pVTZ) analysis, the direct donation gives a prevailing contribution to Sn-N bonding, decreasing the net charge on Sn from formal +2 to +1.28. The substitution effects at the pyrrole rings are discussed. The ability of different theoretical methods to predict the structure of this compound is analyzed.