Dioxygen activation at mononuclear nonheme iron active sites: enzymes, models, and intermediates.

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

6.1.2. Aqueous V(III) Chemistry 877 6.1.3. Oxidation State of Vanadium in Tunicates 878 6.1.4. Uptake of Vanadate into Tunicates 879 6.1.5. Vanadium Binding Proteins: Vanabins 879 6.1.6. Model Complexes and Their Chemistry 880 6.1.7. Catechol-Based Model Chemistry 880 6.1.8. Vanadium Sulfate Complexes 881 6.2. Fan Worm Pseudopotamilla occelata 883 7. Vanadium Nitrogenase 883 7.1. Nitrogenases 883 7.2. Biochemistry of Nitrogenase 884 7.3. Clusters in Nitrogenase and Model Systems: Structure and Reactivity 885

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The chemistry and biochemistry of vanadium and the biological activities exerted by vanadium compounds.

Recent development of polymer electrolyte membranes for fuel cells.

Light-Emitting Self-Assembled Materials Based on d(8) and d(10) Transition Metal Complexes.

Structure and stability of C24 and B12N12 isomers

Five new (μ-oxo)diiron(III) complexes of the capping tetradentate ligand tris(2-pyridylmethyl)amine (tpa) have been prepared. The diaquo complex [tpa(H 2 O)FeOFe(H 2 O)tpa](ClO 4 ) 4 (1) and its conjugate base [tpa(OH)FeOFe(H 2 O)tpa] (ClO 4 ) 3 (2) serve as useful starting materials for the preparation of other (μ-oxo)-bridged diiron(III) complexes of tpa containing either terminal ligands or an auxiliary bridging group. For example, the terminal water ligands of 1 can be replaced by chloro ligands to give monobridged [tpa(Cl)FeOFe(Cl)tpa] (ClO 4 ) 2 (3) or by sulfato to give dibridged [(tpa)FeO(SO 4 )Fe(tpa)] (ClO 4 ) 2 (4)

Synthesis and Reactivity of (.mu.-Oxo)diiron(III) Complexes of Tris(2-pyridylmethyl)amine. X-ray Crystal Structures of [tpa(OH)FeOFe(H2O)tpa](ClO4)3 and [tpa(Cl)FeOFe(Cl)tpa](ClO4)2

Synthesis and Characterization of Bis(.mu.-oxo)dimanganese(III,III), -(III,IV), and -(IV,IV) Complexes with Ligands Related to N,N'-Bis(2-pyridylmethyl)-1,2-ethanediamine (Bispicen)

Iron(II) complexes of the pentadentate ligand N-methyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine (L2) and the potentially hexadentate ligand N,N′-bis(6-methyl-2-pyridylmethyl)-N,N′-bis(2-pyridylmethyl)-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine (L1) have been isolated. Both ligands behave as pentadentate ligands in their iron(II) complexes with the general formulation [FeL(X)]n+(L = L1 or L2, n= 1 or 2) with the sixth co-ordination site (X) occupied by an auxiliary ligand e.g. H2O, Cl, SCN or CN. The crystal structure of [FeL1(H2O)][PF6]2·H2O 1 shows that the nitrogen atom of one of the 6-methyl-2-pyridylmethyl groups of the formally hexadentate ligand is not co-ordinated to the iron atom. Instead a water molecule occupies the sixth co-ordination position. Complex 1 crystallizes in the triclinic space group P, with a= 10.485(2), b= 13.161(5), c= 14.853(6)A, α= 69.31(4), β= 74.42(3), γ= 66.37(3)° and Z= 2. The structure refined to a final R value of 0.052 for 2531 reflections. The complexes show peroxidase activity, the availability of a labile site on the relatively stable iron(II) complexes, along with no apparent tendency to form oxo-bridged diiron(III) species, which are likely to be crucial factors in the mechanism of the oxidation reactions. Efforts to isolate a complex with a co-ordinated peroxide in the sixth position were unsuccessful. However, we have spectroscopic evidence that peroxide reacts with the iron(II) complexes to form an unstable species, probably of the form [FeIIIL(OOR)]2+(L = L1 or L2, R = H or But). The peroxide ligand in this iron(III) complex is likely to be forced into an ‘end-on’ co-ordination mode.

Iron(II) complexes of polydentate aminopyridyl ligands and an exchangeable sixth ligand; reactions with peroxides. Crystal structure of [FeL1(H2O)][PF6]2·H2O [L1=N,N′-bis-(6-methyl-2-pyridylmethyl)-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine]

A procedure is presented that allows us to simulate from first principles the normalized spectra of nuclear inelastic scattering (NIS) of synchrotron radiation by molecular crystals containing a M\"ossbauer isotope. Neglecting intermolecular vibrations the NIS spectrum is derived from the normal modes of the free molecule, that are calculated with the density-functional method B3LYP. At low temperatures the inelastic part of the calculated NIS spectrum is a superposition of peaks that correspond to the individual vibrational modes of the molecule. The area of each peak is proportional to that part of the mean-square displacement of the M\"ossbauer isotope that is due to the corresponding vibrational mode. Angular-dependent NIS spectra have been recorded for a guanidinium nitroprusside single crystal and temperature-dependent NIS spectra for the spin-crossover system $[\mathrm{Fe}(\mathrm{tpa})(\mathrm{NCS}{)}_{2}]$ [tpa=tris(2-pyridylmethyl)amine]. Qualitative agreement is achieved between measured and simulated spectra for different crystal orientations of guanidinium nitroprusside. A remarkable increase of the iron-ligand bond stretching upon spin crossover has unambiguously been identified by comparing the measured NIS spectra of $[\mathrm{Fe}(\mathrm{tpa})(\mathrm{NCS}{)}_{2}]$ with the theoretical simulations.

Hans Toftlund

Papers

Structure and stability of C24 and B12N12 isomers

Synthesis and Reactivity of (.mu.-Oxo)diiron(III) Complexes of Tris(2-pyridylmethyl)amine. X-ray Crystal Structures of [tpa(OH)FeOFe(H2O)tpa](ClO4)3 and [tpa(Cl)FeOFe(Cl)tpa](ClO4)2

Synthesis and Characterization of Bis(.mu.-oxo)dimanganese(III,III), -(III,IV), and -(IV,IV) Complexes with Ligands Related to N,N'-Bis(2-pyridylmethyl)-1,2-ethanediamine (Bispicen)

Iron(II) complexes of polydentate aminopyridyl ligands and an exchangeable sixth ligand; reactions with peroxides. Crystal structure of [FeL1(H2O)][PF6]2·H2O [L1=N,N′-bis-(6-methyl-2-pyridylmethyl)-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine]

Measurement and simulation of nuclear inelastic-scattering spectra of molecular crystals