Search

Experimental data and theoretical calculations have failed to rationalize the role of covalnecy in real experimental BTP (2,6-Di(1,2,4-trianzin-3-yl)pyridine) complexes. DFT calculations on [M(BTP).sub.3].super.3} (M-La, U, Cm, Gd) were used to show that even if back-bonding effects are significant in the U-BTP bond, it is the contrast of donation on 6d and 5f [Cm.super.III] orbitals that explains, at least in part, its selective complexation to BTP.

Research has been conducted on the triosodide octanocoordinated uranium(III) complexes and their lanthanum(III) analogues. The crystal structures of these complexes has been investigated and the details are reported.

Research was conducted to examine various spectroscopic studies of WOs and MoRu porphyrin dimers using variable-temperature 1H NMR, resonance Raman, magnetic susceptibility and X-ray crystallography. The objective was to determine a proper molecular orbital diagram for the dimers. Results demonstrate an unusual molecular orbital diagram which has never been observed before in metal-metal bonded metalloporphyrin dimers.

Research was conducted to examine the magnetic properties of several mixed-valent diruthenium long-chain carboxylates with the general formula Ru2(RCO2)4X in temperatures ranging from 6-400 K. Magnetic susceptibility calculations were performed on the carboxylates. The columnar mesophase of the mesomorphic congeners suggests that there is no substantial structural change that takes place at the crystal-liquid crystal transition.

Chemical research has established the solid state magnetic susceptibility properties of group eight metal-to-metal doubly bonded porphyrin and tetraazaporphyrin dimers [Ru(Octaethylporphyrin)]2, Ru(octaethyltetraazaporphyrin)]2 and [Os(OEP)]. Nuclear magnetic resonance analysis indicates that each of the group eight dimers exhibits similar behaviour in zero-field splitting of the triplet ground electronic state.

The f-f transitions of a series of rare earth aquo and chloro complexes were theoretically evaluated to find out the experimental uncertainties concerning the coordination mode of trivalent plutonium in concentrated LiCl. The nephelauxetic effect from aquo to chloro complexes is clearly observed through both spectral red shifts and the decrease in [Fe.sub.2], the Slater-Condon parameter.

A theoretical and experimental study was conducted to determine the electronic, magnetic, and spectroscopic properties of mixed valent and divalent binuclear diruthenium tetracarboxylates. Using ZINDO/S-MRCI and DFT calculations, it was found that both divalent species have ground-state configuration and have robust Zero Field Splitting. Findings also indicate that a balance between the Ru-Ru and Ru-O (equatorial carboxylate) bond strengths is the major factor that determines their structural and spectroscopic properties.

The design of bistable magnetic systems should enable the storage of information by manipulation of the spin degrees of freedom. However, such a strategy relies on the preparation of target objects, whose environment must be controlled to favor a hysteretic behavior. Here, we report the successful modeling of a highly cooperative two-step spin-crossover iron(II) compound, [Fe(bapbpy)(NCS)2]. The magnetic susceptibility measurements and low- and high-temperature hysteretic cycles reflect the presence of an intermediate phase, which controls the memory-storage capacity of this material. It is shown that the hysteresis loop widths can be traced theoretically by evaluating the electrostatic contributions between the transiting units. Despite the apparent reduction of intermolecular interactions upon cooling, it is suggested that the enhanced fluctuations of the Madelung field are responsible for the observed hysteresis width changes. This counterintuitive scenario makes the preparation of information storage devices an even more challenging task, where theoretical inspections are very insightful. [ABSTRACT FROM AUTHOR]

The As III binding of two NTA-based tripodal pseudopeptides, possessing three cysteine (ligand L 1 ) or d-penicillamine residues (ligand L 2 ) as potential coordinating groups for soft semimetals or metal ions, was studied by experimental (UV, CD, NMR, and ESI-MS) and theoretical (DFT) methods. All of the experimental data, obtained with the variation of the As III :ligand concentration ratios or pH values in some instances, evidence the exclusive formation of species with an AsS 3 -type coordination mode. The UV-monitored titration of the ligands with arsenous acid at pH = 7.0 provided an absorbance data set that allowed for the determination of apparent stability constants of the forming species. The obtained stabilities (log K ' = 5.26 (As L 1 ) and log K ' = 3.04 (As L 2 )) reflect high affinities, especially for the sterically less restricted cysteine derivative. DFT calculated structures correlate well with the spectroscopic results and, in line with the 1 H NMR data, indicate a preference for the all- endo conformers resembling the As III environment at the semimetal binding sites in various metalloproteins.

Nickel superoxide dismutase (NiSOD) is an enzyme that protects cells against O 2 · - . While the structure of its active site is known, the mechanism of the catalytic cycle is still not elucidated. Its active site displays a square planar Ni II center with two thiolates, the terminal amine and an amidate. We report here a bioinspired Ni II complex built on an ATCUN-like binding motif modulated with one cysteine, which demonstrates catalytic SOD activity in water ( k cat = 8.4(2) × 10 5 M -1 s -1 at pH = 8.1). Its reactivity with O 2 · - was also studied in acetonitrile allowing trapping two different short-lived species that were characterized by electron paramagnetic resonance or spectroelectrochemistry and a combination of density functional theory (DFT) and time-dependent DFT calculations. Based on these observations, we propose that O 2 · - interacts first with the complex outer sphere through a H-bond with the peptide scaffold in a [Ni II O 2 · - ] species. This first species could then evolve into a Ni III hydroperoxo inner sphere species through a reaction driven by protonation that is thermodynamically highly favored according to DFT calculations.

Solution (VT NMR, Evans method magnetic susceptibility, resonance Raman) and solid-state (SQUID magnetic susceptibility, X-ray crystallography) spectroscopic studies of intertriad heterodimeric [(OEP)MoRu(OEP)] (1), [(OEP)WOs(OEP)] (2), and [(OEP)MoRu(TPP)]PF(6) (3(+)) metalloporphyrins are reported (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato; TPP = 5,10,15,20-tetraphenylporphyrinato). Solution and solid-state magnetic susceptibility data indicate that 1 and 2 contain two unpaired electrons in the ground electronic configuration. The presence of a delta bond in 3(+) has been confirmed by structural characterization. The experimental evidence is consistent with a molecular orbital ordering, sigma < pi < delta < pi < delta, which is different from that seen for homologous metalloporphyrin dimers with homometallic or intratriad heterometallic multiple metal-metal bonds. Resonance Raman data suggest that the heterometallic bonds are slightly stronger than isoelectronic homometallic species.