%0 Journal Article %1 Ernst.1996 %A Ernst, Sylvia %A Vogler, Conny %A Klein, Axel %A Kaim, Wolfgang %A Zalis, Stanislav. %D 1996 %J Inorganic Chemistry %K EPR MO ab carbonyl chromium complex crossing deriv deriv;MO diazaphenanthroline initio initio;ENDOR initio;diazaphenanthroline initio;molybdenum initio;tungsten metal phenanthroline %N 5 %P 1295--1300 %R 10.1021/IC950892H %T The p* Molecular Orbital Crossing a2(q)/b1(y) in 1,10-Phenanthroline Derivatives. Ab Initio Calculations and EPR/ENDOR Studies of the 4,7-Diaza-1,10-phenanthroline Radical Anion and Its M(CO)4 Complexes (M = Cr, Mo, W) %V 35 %X Ab initio, semiempirical, and HMO perturbation calcns. were employed to assess the relative positioning of the closely situated low-lying unoccupied p* MOs a2(q) and b1(y) in 1,10-phenanthroline (phen) and its 3,4,7,8-tetra-Me (tmphen) and four sym. diaza derivs. (n,m-dap). Compared to a2(q), the b1(y) p MO is distinguished by markedly higher MO coeffs. at the chelating nitrogen p centers in 1,10-positions; eventually, a higher Coulomb integral value at those positions will thus always favor the lowering of b1 beyond a2. Using the Coulomb integral parameter at the chelating 1,10-nitrogen p centers as the HMO perturbation variable, the crossing of both energy levels in terms of decreasing preference for the a2(q) over the b1(y) orbital as the LUMO follows the sequence 5,6-dap \textgreater 2,9-dap \textgreater 4,7-dap \textgreater phen \textgreater 3,8-dap. The calcns. reveal a2(q) as the LUMO in 5,6-dap for all reasonable perturbation parameters, in agreement with previous observations for ruthenium(II) complexes which reveal a discrepancy between the lowest-lying \dqredox p* orbital\dq (a2) and the \dqoptical p* MO\dq (b1) to which the most intense low-energy MLCT transition occurs. According to the HMO calcns., the situation is more ambiguous for the 4,7-dap analog, yet EPR/ENDOR studies clearly show that the one-electron-reduced ligand and its tetracarbonylmetal(0) complexes (Cr, Mo, W) have the b1(y) orbital singly occupied. Only ab initio calcns. with double-z basis and inclusion of d polarization functions reproduced correctly the exptl. obsd. orbital ordering for tmphen (a2 \textgreater b1) and for phen and 4,7-dap (b1 \textgreater a2). on SciFinder(R)

@article{Ernst.1996, abstract = {Ab initio, semiempirical, and HMO perturbation calcns. were employed to assess the relative positioning of the closely situated low-lying unoccupied \textgreek{p}* MOs a2(\textgreek{q}) and b1(\textgreek{y}) in 1,10-phenanthroline (phen) and its 3,4,7,8-tetra-Me (tmphen) and four sym. diaza derivs. (n,m-dap). Compared to a2(\textgreek{q}), the b1(\textgreek{y}) \textgreek{p} MO is distinguished by markedly higher MO coeffs. at the chelating nitrogen \textgreek{p} centers in 1,10-positions; eventually, a higher Coulomb integral value at those positions will thus always favor the lowering of b1 beyond a2. Using the Coulomb integral parameter at the chelating 1,10-nitrogen \textgreek{p} centers as the HMO perturbation variable, the crossing of both energy levels in terms of decreasing preference for the a2(\textgreek{q}) over the b1(\textgreek{y}) orbital as the LUMO follows the sequence 5,6-dap {\textgreater} 2,9-dap {\textgreater} 4,7-dap {\textgreater} phen {\textgreater} 3,8-dap. The calcns. reveal a2(\textgreek{q}) as the LUMO in 5,6-dap for all reasonable perturbation parameters, in agreement with previous observations for ruthenium(II) complexes which reveal a discrepancy between the lowest-lying {\dq}redox \textgreek{p}* orbital{\dq} (a2) and the {\dq}optical \textgreek{p}* MO{\dq} (b1) to which the most intense low-energy MLCT transition occurs. According to the HMO calcns., the situation is more ambiguous for the 4,7-dap analog, yet EPR/ENDOR studies clearly show that the one-electron-reduced ligand and its tetracarbonylmetal(0) complexes (Cr, Mo, W) have the b1(\textgreek{y}) orbital singly occupied. Only ab initio calcns. with double-\textgreek{z} basis and inclusion of d polarization functions reproduced correctly the exptl. obsd. orbital ordering for tmphen (a2 {\textgreater} b1) and for phen and 4,7-dap (b1 {\textgreater} a2). [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Ernst, Sylvia and Vogler, Conny and Klein, Axel and Kaim, Wolfgang and Zalis, Stanislav.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/20c7885dd81bf307061c8a0f5e6ca1db4/huebleriac}, doi = {10.1021/IC950892H}, interhash = {554c893c1331bbf0702878fe51b680a4}, intrahash = {0c7885dd81bf307061c8a0f5e6ca1db4}, issn = {0020-1669}, journal = {Inorganic Chemistry}, keywords = {EPR MO ab carbonyl chromium complex crossing deriv deriv;MO diazaphenanthroline initio initio;ENDOR initio;diazaphenanthroline initio;molybdenum initio;tungsten metal phenanthroline}, number = 5, pages = {1295--1300}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {The \textgreek{p}* Molecular Orbital Crossing a2(\textgreek{q})/b1(\textgreek{y}) in 1,10-Phenanthroline Derivatives. Ab Initio Calculations and EPR/ENDOR Studies of the 4,7-Diaza-1,10-phenanthroline Radical Anion and Its M(CO)4 Complexes (M = Cr, Mo, W)}, volume = 35, year = 1996 }