Functional Theory Geometry Optimization Calculations Research Articles

Molecular structure of W(PMe3)3H6 in the solid state and in solution

The molecular structure of W(PMe3)3H6 has been identified by low temperature (−123°C) X-ray diffraction studies as a classical hydride compound, with a tricapped trigonal prismatic geometry in which two of the PMe3 ligands adopt eclipsed positions on opposite triangular faces of the prism and one PMe3 ligand caps a rectangular face. The solid state structure is reproduced well by density functional theory geometry optimization calculations on the molecule in the gas phase. NMR spectroscopic studies provide evidence that W(PMe3)3H6 also exists as a classical hydride compound in solution. For example, the T1(min) value for the hydride ligands of W(PMe3)3H6 is 380ms at 500MHz and 310ms at 400MHz, values that are more in accord with a classical hydride formulation than a nonclassical one. Likewise, the W(PMe3)3H6−xDx isotopologues (obtained by isotope exchange with either deuterobenzene or deuterotoluene) exhibit upfield (+13ppb) deuterium secondary isotope effects on the hydride chemical shift, which are also consistent with a classical description.

Synthesis and structural characterization of [Bse Me]Ni(PPh 3)(NO), a nickel complex with a bent nitrosyl ligand

The nickel nitrosyl compound [Bse Me]Ni(PPh 3)(NO) has been synthesized by the reaction of Ni(PPh 3) 2(NO)Br with potassium bis(2-seleno-1-methylimidazolyl)hydroborate, [Bse Me]K. X-ray diffraction studies demonstrate that (i) the B–H group of the [Bse Me] ligand interacts with the nickel center and (ii) the nitrosyl ligand is bent, with Ni–N–O bond angles of 149.1(3)° and 153.1(3)° for the two crystallographically independent molecules. The bent nature of the nitrosyl ligand in [Bse Me]Ni(PPh 3)(NO) is in marked contrast to the linearity observed for the tris(2-seleno-1-mesitylimidazolyl)hydroborato counterpart [Tse Mes]NiNO (180.0°). Density functional theory geometry optimization calculations demonstrate that the Ni⋯H–B interaction is not responsible for causing the nitrosyl ligand to bend, but rather the difference between [Tse Mes]NiNO and [Bse Me]Ni(PPh 3)(NO) is due to the [Tse Mes] ligand allowing the former molecule to adopt a structure with C 3 symmetry. In contrast, the steric and electronic asymmetry of [Se 2P] donor array of the [Bse Me] and PPh 3 ligand combination prevents [Bse Me]Ni(PPh 3)(NO) from having C 3 symmetry and the nitrosyl ligand bends to stabilize the occupied M–N σ ∗ antibonding orbital.

Stability and structure of Ni+Arn and Pt+Arn clusters

The mass spectra of argon clusters doped with d9 transition metal ions, Ni+Arn and Pt+Arn, show pronounced intensity at n=4 and n=6. Density functional theory geometry optimization calculations in Ni+Arn support a square planar geometry for Ni+Ar4 and an elongated octahedron for Ni+Ar6.