Quantum-chemical calculations with gradient-corrected (B3LYP) density functional theory have been carried out for iron bispentazole and ferrocene. The calculations predict that Fe(eta5-N5)2 is a strongly bonded complex which has D5d symmetry. The theoretically predicted total bond energy that yields Fe in the 5D ground state and two pentazole ligands is Do = 109.0 kcal mol(-1), which is only 29 kcal mol(-1) less than the calculated bond energy of ferrocene (Do = 138.0 kcal mol(-1); experimental: 158 +/- 2 kcal mol(-1)). The compound Fe(eta5-N5)2 is 260.5 kcal mol(-1) higher in energy than the experimentally known isomer Fe(N2)5, but the bond energy of the latter (Do = 33.7 kcal mol(-1)) is much less. The energy decomposition analyses of Fe(eta5-N5)2 and ferrocene show that the two compounds have similar bonding situations. The metal-ligand bonds are roughly half ionic and half covalent. The covalent bonding comes mainly from (e1g) eta5-N5- --> Fe2+ pi-donation. The previously suggested MO correlation diagram for ferrocene is nicely recovered by the Kohn-Sham orbitals. The calculated vibrational frequencies and IR intensities are reported.

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Quantum chemical DFT calculations using B3LYP and BP86 functionals have been carried out for the title compounds. The equilibrium geometries and bond dissociation energies are reported. The metal-ligand bonding was analyzed with an energy partitioning method. The strongest bonded homoleptic complex with a heterocyclic ligand is Fe(η 5 -P 5 ) 2 . The bond dissociation energy yielding the Fe atom and two cyclo-P 5 ligands (D o ) 128.3 kcal/mol) is nearly the same as for ferrocene (D o ) 131.3 kcal/mol). The nitrogen, arsenic, and antimony analogues of Fe(η 5 -E 5 ) 2 have significantly weaker metal-ligand bonds, which, however, should still be strong enough to make them isolable under appropriate conditions. The calculated heats of formation show also that the phosphorus complex is the most stable species of the heterocyclic Fe(η 5 -E 5 ) 2 series. The Fe-(η 5 -E 5 ) bonding in the mixed sandwich complexes FeCp(η 5 -E 5 ) is much stronger compared to the homoleptic molecules. The heterocyclic ligands cyclo-E 5 in the mixed complexes FeCp(η 5 -E 5 ) bind as strongly or in case of phosphorus even stronger than one Cp ligand does in FeCp 2 except for E ) Sb. The metal fragments Fe(η 5 -E 5 ) + have a pyramidal geometry except for E ) Sb, which is predicted to be a planar ion with D 5h symmetry. The energy partitioning shows that the binding interactions between the closed shell cyclo-E 5ligand and the Fe(η 5 -E 5 ) + fragment do not change very much for the different ligand atoms E in the homoleptic and heteroleptic complexes. The bonding comes from 53%-58% electrostatic attraction, while 42%-47% come from covalent interactions. The latter contribution comes mainly from the donation of the occupied e 1 (π) orbital of the ligand into the empty orbital of the metal fragment.

We report about quantum chemical ab initio calculations at the MP2/6-311ϩG(2d)//MP2/6-31G(d) level and DFT calculations at BP86/TZP of the geometries and bond dissociation energies of the borane-phosphane complexes X 3 B-PY 3 and the alanephosphane complexes X 3 Al-PY 3 (X ϭ H, F, Cl; Y ϭ F, Cl, Me, CN). The nature of the B-P and Al-P bonds is analyzed with a bond energy partitioning method. The calculated bond dissociation energies D e of the borane adducts X 3 B-PY 3 show for the phosphane ligands the trend PMe 3 > PCl 3~P F 3 > P(CN) 3 . A similar trend PMe 3 > PCl 3 > PF 3 > P(CN) 3 is predicted for the alane complexes X 3 Al-PY 3 . The order of the Lewis acid strength of the boranes depends on the phosphane Lewis base. The boranes show with PMe 3 and PCl 3 the trend BH 3 > BCl 3 > BF 3 but with PF 3 and P(CN) 3 the order is BH 3 > BF 3 > BCl 3 . The bond energies of the alane complexes show always the trend AlCl 3 Ն AlF 3 > AlH 3 . The bonding analysis shows that it is generally not possible to correlate the trend of the bond energies with one single factor which determines the bond strength. The preparation energy which is necessary to deform the Lewis acid and Lewis base from the equilibrium form to the geometry in the complex may have a strong Theoretische Studien anorganischer Verbindungen. 19. Quantenchemische Untersuchungen der Phosphankomplexe X 3 B-PY 3 und X 3 Al-PY 3 (X ‫؍‬ H, F, Cl; Y ‫؍‬ F, Cl, Me, CN) Inhaltsübersicht. Wir berichten über quantenchemische Ab-initioBerechnungen auf MP2/6-311ϩG(2d)//MP2/6-31G(d) Niveau und über DFT-Rechnungen mit BP86/TZP mit denen die Geometrien und Bindungsdissoziationsenergien der Boran-Phosphan-Komplexe X 3 B-PY 3 und der Alan-Phosphan-Komplexe X 3 Al-PY 3 (X ϭ H, F, Cl; Y ϭ F, Cl, Me, CN) ermittelt wurden. Die Natur der B-P und Al-P Bindungen wird mit Hilfe einer Energiepartitionierung analysiert. Die berechneten D e -Werte der Boranaddukte X 3 B-PY 3 weisen für die Phosphanliganden den Trend PMe 3 > PCl 3~P F 3 > P(CN) 3 auf. Ein ähnlicher Trend PMe 3 > PCl 3 > PF 3 > P(CN) 3 wird für die Alankomplexe X 3 Al-PY 3 berechnet. Die Reihenfolge der Lewissäure-Stärke der Borane hängt von der Natur der Phosphan-Lewisbase ab. Mit PMe 3 und PCl 3 nimmt die Stärke in der Reihe BH 3 > BCl 3 > BF 3 ab während mit PF 3 and P(CN) 3 die Reihenfolge BH 3 > BF 3 > BCl 3 ist. Die Bindungsenergien der Alankomplexe haben immer den Trend AlCl 3 Ն AlF 3 > AlH 3 . Die Bindungsanalyse zeigt dass die Abnahme der Bindungsenergien im allgemeinen nicht mit einem einzelnen Faktor erklärt werden kann. Die Präparierungsenergie, die aufgebracht werden muss um die Le-1294 influence on the bond energies. The intrinsic interaction energies may have a different order than the bond dissociation energies. The trend of the interaction energies are sometimes determined by a single factor (Pauli repulsion, electrostatic attraction or covalent bonding) but sometimes all components are important. The higher Lewis acid strength of BCl 3 compared with BF 3 in strongly bonded complexes is not caused by t...

Quantum chemical calculations using gradient-corrected DFT at the BP86/TZ2P level of the compounds [Ti(eta(5)-E(5))(2)](2)(-) (E = CH, N, P, As, Sb) are reported. The nature of the metal-ligand bonding has been analyzed with an energy decomposition method, and the results are compared with [Fe(eta(5)-E(5))(2)]. The bonding in both series of complexes is more covalent than electrostatic. The energy decomposition analysis shows that the dominant orbital interactions in the negatively charged titanium species come from the (e(2)') Ti --> [(eta(5)-E(5))(2)](2)(-) back-donation (delta bonding) while the covalent bonding in the iron complexes come mainly from (e(1)' ') (Cp(-))(2) --> Fe(2+) donation (pi bonding). The nature of the metal-ligand interactions does not change very much for different ligands cyc-E(5) within the two series of compounds. The calculated bond dissociation energies for breaking one metal-ligand bond of the molecules [Ti(eta(5)-E(5))(2)](2)(-) shows for E the order P > As > Sb >> N >> CH. The central message of this work is that the complexes [Ti(eta(5)-E(5))(2)](2)(-) are delta bonded molecules.