Joachim Reinhold

Quantum chemical investigations of the π-acceptor ability of α-diimine ligands

Abstract The bonding properties of α-diimine complexes of transition metals in low oxidation states are essentially determined by π-back donation. The energies of the lowest unoccupied molecular orbitals of the ligands have been used to estimate their acceptor ability. MO calculations of selected α-diimines are reported in the present paper. N-unsubstituted and apliphatic diimines are found to be better π-acceptors than 2,2′-bipyridine which is in agreement with experimental results. It turns out that the LUMO energies calculated by the NDDO method are a good measure for the π-acceptor behaviour of ligands with similar structure towards transition metal ions.

Q-Band single-crystal EPR study and molecular orbital calculations of [(C6H5)4As][ReVINCl4/ReVOCl4]

Abstract A Q -band single-crystal EPR study of tetraphenylarsoniumtetrachloro-nitridorhenate(VI), [(C 6 H 5 ) 4 As][Re VI NCl 4 ], diamagnetically diluted by the isoelectronic oxorhenate(V) complex is reported. The EPR spectra are typical of an ion with 5d 1 ( S =1/2) configuration and are influenced by large rhenium hyperfine coupling constants and nuclear quadrupole interactions. They are characterized by well-resolved 185,187 Re hyperfine patterns with almost equal spacings and the occurrence of “forbidden” transitions ( Δm I =±1, Δm I =±2). The 185,187 Re hyperfine parameters as well as the data obtained from density functional theory (DFT) and the extended Huckel theory (EHT) molecular orbital calculations are used to analyze the spin density distribution in the system under study. Thereby, the negative sign found for the spin density at the nitrogen from DFT is mainly determined by spin polarization. In addition, both MO methods are used to calculate the electric field gradient being responsible for the 185,187 Re nuclear quadrupole coupling.

Unexpected reaction of [Ni(CO)4-n(R2PCl)n] (n = 1, 2 ; R = But, Cy, Ph) with Na2[Fe2(CO)8]. Synthesis and electronic structure of the anions [Fe2(μ-CO)(CO)6(μ-PR2)]- and their reactions with H+ and [M(PPh3)]+ (M = Cu, Ag, Au)

Treatment of [Ni(CO)4-n(R2PCl)n] (n = 1, 2; R = Bu(t), Cy, Ph) with Na2[Fe2(CO)8] gave, depending on n and R, either the doubly phosphido-bridged complexes [Fe2(CO)6(mu-PR2)2] or the anions [Fe2(mu-CO)(CO)6(mu-PR2)]-. These anions can also be obtained by the reaction of [Fe(CO)4(PR2)]- with either [Fe2(CO)9] or [Fe(CO)5] via the intermediate [Fe2(CO)8(mu-PR2)]-. The electronic structure of the anions [Fe2(mu-CO) (CO)6(mu-PR2)]- has been studied by an EHT calculation which supports their ambident oxygen- or metal-nucleophilicity. The metal-centred nucleophilic reactions of the anion [Fe2(mu-CO)(CO)6(mu-PBu(t)2)]- with H+ and [M(PPh3)]+, (M = Cu, Ag, Au), respectively, are described. The new complexes have been characterized by various spectroscopic methods and the structure of [Fe2{mu-Ag(PPh3)}(mu-CO)(CO)6(mu-PBu(t)2)] has been established by X-ray analysis.

Application of the NDDO method to transition metal compounds

The NDDO method has been extended to include elements withd-orbitals. A parametrization for the first-row transition metals is given, which has been worked out to describe structural properties of transition metal complexes. Applications of the method to the Jahn-Teller distortions of tetrachloro complexes are presented. The NDDO results are compared with those from CNDO and INDO calculations. It turns out that the NDDO method seems to be the most sensitive among the ZDO procedures.

A Stable and Crystalline Triarylgermyl Radical: Structure and EPR Spectra†

A radical thing: After being obtained unexpectedly in low yields, the synthesis of the first stable triarylgermyl radical (*)Ge[3,5-tBu(2)-2,6-(EtO)(2)C(6)H](3) (1; C gray, O blue) was considerably optimized, and the product was investigated by X-ray analysis and EPR spectroscopy. The results were compared with DFT-MO studies for the model compound (*)Ge[2,6-(MeO)(2)C(6)H(3)].

Effects of the bridging ligands on the molecular and electronic structure of Fe2(CO)9 derivatives

Abstract This article reviews the structural and electronic properties of Fe 2 (CO) 9 derivatives with any triad of σ donor and π acceptor bridges selected from the series CO, CH 2 , CF 2 , SiMe 2 , GeMe 2 , InMe and CS. Based on the available structural data and computational results, the bridges other than CO can be catalogued in two different groups. The ligands of group I feature a pivotal carbon atom such as the CO ligand itself (i.e. L=CH 2 , CF 2 and CS). Those of group II are characterized by different hetero-atoms at the core of the bridging group (i.e. L=SiMe 2 , GeMe 2 and InMe). The geometry of the inner Fe(μ-L) 3 Fe skeleton changes significantly between the members of the different series. In particular, the range of Fe–Fe distances can be as large as 52.3 pm, the higher and lower limits being found in the system with three InMe bridges and in that with one CO and two CF 2 ligands, respectively. It turns out that ligands of group I favor the decrease of the Fe–Fe distance compared to the parent compound Fe 2 (CO) 9 . On the contrary, those of group II favor a larger intermetallic separation. By detailed analyses, the structural effects can be traced back to the σ donor and π acceptor capabilities of the different bridges.

Extended hückel calculation on diimine substituted oxalate cobalt(III) complexes

Abstract Tris(oxalato)cobaltate(III) is known a typical thermo- and photoreactive compound. Substitution of oxalato by α-diimines reduces the thermally induced redox decomposition. EHT calculation on diimine substituted Co(III) complexes with different aliphatic and aromatic diimine ligands have been carried out. It results in the EHT-LUMO energies being able to be used to estimate the thermodynamic redox stability of the mixed ligand complexes and are helpful for planned syntheses of photocatalytically interesting systems.

Characterization of the mercaptobenzothiazole bonding on cadmiumsulfide by MO interpretation of N K XANES results

The X-ray absorption near-edge structures (XANES) at the nitrogen K-edge of mercaptobenzothiazole (MBT), its anion, a chelate complex of this molecule, and its adsorbate on CdS(1010) exhibit distinct qualitative differences and characteristic peak shifts. It is shown that density functional theory (DFT) calculations of the respective systems in their electronic ground state can lead to an understanding of these spectral features. Their interpretation in terms of excitations into virtual molecular orbitals allows the assignment of the signals to functional groups in the chemical systems. By this means, the spectroscopic information on the adsorbate structure is confirmed and rationalized on a theoretical basis. It is deduced from the spectra that MBT is definitely adsorbed in its anionic form.

An extension of the fenske-hall LCAO method for approximate calculations of inner-shell binding energies of molecules

Abstract The approximate LCAO MO method of Fenske and Hall has been extended to an all-election method allowing the calculation of inner-shell binding energies of molecules and their chemical shifts. Preliminary results are given.

The nature of gas-phase complexes R3PHX (RH, CH3; XCl, Br, I)

Abstract There is no evidence for the existence of an ion-pair complex R3PH+X− in the gas phase. The corresponding minimum on the SCF potential surface in the case of RCH3 disappears after inclusion of correlation energy contributions.