Secrets of solid state and aqueous solution structures of [Ni(tmdta)](2-).

The molecular structures of Li2[Ni(tmdta)]·5H2O (1a, tmdta = trimethylenediaminetetraacetate), {C(NH2)3}2[Ni(tmdta)]·6H2O (1b), and {Ni(H2O)6}[Ni(tmdta)]·2H2O (2a) have been determined. The central trimethylenediamine chelate ring shows half-chair (hc) geometries in 1a and 1b, while a twist-boat (tb) conformation is encountered in 2a. The coexistence of tb and hc forms in the solid state prompted us to elucidate the existence of a tb ⇌ hc equilibrium in aqueous solution. Evaluation of the data from solid state vibrational spectra (Raman and IR) for the hc and tb forms showed excellent agreement with simulated spectra obtained with DFT computations (TPSSh/TZVP). This outstanding matching between theory and experiment enabled us to build composite spectra with varying hc:tb ratios. Comparison of these results with Raman and IR spectra recorded for [Ni(tmdta)](2-) in aqueous solution revealed that simulated Raman and IR spectra with a hc:tb ratio = 2:3 match the solution spectra in an accurate way. This equilibrium ratio enabled us to compute (13)C NMR sifts for the paramagnetic solution spectrum of [Ni(tmdta)](2-) based on the relative contributions by hc and tb fractions. This leads to computed shifts that agree closely with the experimental ones. Also, the kinetics of the skeleton dynamics could be estimated quantitatively by temperature-dependent (13)C NMR spectroscopic measurements. An interesting effect encountered for the very first time here concerns a drastic intensity difference of the 10Dq band ((3)A2g → (3)T2g(F) transition) in solid state electronic spectra of tb vs hc isomers, where the intensity of this band in the case of the hc form is much lower than that of the tb conformer and thus more similar to the case of the usual Ni(II) chromophore in octahedral environment. The equilibrium constants for complex formation and protonation of Ni(II)-tmdta at low pH have been estimated by pH-dependent UV-vis titration experiments. Correlation of these data with those of Ni(II)-edta and related 3d M(II) edta and tmdta complexes allow important conclusions on the consequences resulting from extending the central diamine ring in the ligand by one methylene group in terms of both complex and protolytic stability for edta vs tmdta complexes.

Synthesis and crystal structure of a "FeBi" cluster compound with noncovalent low-valent Bi···π(arene) interactions.

We describe the synthesis and structural characterization of the unprecedented [Bi4Fe3(CO)9] cluster, the low-valent Bi atoms of which are involved in the types of previously not identified intermolecular Bi···π(arene) and ΔBi···π(arene)interactions. Different coordination modes of arene rings bound to Bi atoms were determined.

Alkali-metal-supported bismuth polyhedra-principles and theoretical studies.

We have quantum chemically investigated the structure, stability, and bonding mechanism in highly aggregated alkali-metal salts of bismuthanediide anions [RBi](2-) using relativistic density functional theory (DFT, at ZORA-BP86/TZ2P) in combination with a quantitative energy decomposition analysis (EDA). Our model systems are alkali-metal-supported bismuth polyhedra [(RBi)(n)M(2n-4)](4-) with unique interpenetrating shells of a bismuth polyhedron and an alkali-metal superpolyhedron. Furthermore, we have analyzed the trianionic inclusion complexes [M'@{(RBi)(n)M(2n-4)}](3-) involving an additional endohedral alkali-metal ion M'. The main objective is to assist the further development of synthetic approaches toward this class of compounds. Our analyses led to electron-counting rules relating, for example, the number of bonding orbitals (N(bond)) of the cage molecules [(RBi)(n)M(2n+Q)](Q) to the number of bismuth atoms (n(Bi)), alkali-metal atoms (n(M)), and net charge Q as N(bond) = n(Bi) + n(M) - Q (R = one-electron donor ligand; M = alkali metal; n = 4-12; Q = -4, -6, -8). Finally, on the basis of our findings, we predict the next members in the 5-fold symmetrical row of alkali-metallobismaspheres with a macroicosahedral arrangement.

Synthesis and Cu(II) coordination chemistry of a patellamide derivative: consequences of the change from the natural thiazole/oxazoline to the artificial imidazole heterocycles.

The synthesis and Cu(II) coordination chemistry of the cyclic pseudo-octapeptide H(4)pat(1), a dimethyl-imidazole analogue of naturally occurring cyclic peptides (patellamide A-F, ascidiacyclamide) is reported. Substitution of the oxazoline and thiazole heterocycles by dimethyl-imidazoles leads to a slightly different structure of the macrocycle in the solid state. The Cu(II) coordination chemistry of H(4)pat(1), monitored with high-resolution electrospray mass spectrometry, spectrophotometric titrations, and EPR spectroscopy, revealed the presence of both mono- and dinuclear Cu(II) complexes. The dimethyl-imidazole analogue shows a high cooperativity in Cu(II) coordination, that is, the preferred formation of dinuclear complexes. The dinuclear unbridged Cu(II) complexes of H(4)pat(1) have unusual EPR features, reminiscent of those of patellamide D: the dipole-dipole interaction of the Cu(II) centers is negligible due to the "magic angle" orientation of the two Cu(II) ions. Density functional theory calculations (DFT) are used to model the structures of the Cu(II) complexes, and the structural assignments from the spectroscopic investigations are supported by the optimized and by X-ray structures of the metal-free macrocycle and dinuclear Cu(II) complexes of H(4)pat(1). The rigidity of the dimethyl-imidazole rings has a significant effect on the structures of the metal-free ligands and Cu(II) complexes and therefore changes the properties of these compounds. This may explain why Nature has chosen the thiazole-oxazoline combination for the patellamides and ascidiacyclamide.

Oxidative addition reactions of element-hydrogen bonds with different polarities to a gallium(I) compound.

The gallium(I) derivative [Ga({N(dipp)CMe}(2)CH)] (1; dipp = 2,6-diisopropylphenyl) undergoes facile oxidative addition reactions with various element-hydrogen bonds including N-H, P-H, O-H, Sn-H, and H-H bonds. This was demonstrated by its reaction with triphenyltin hydride, ethanol, water, diethylamine, diphenylphosphane, and dihydrogen. All products were characterized by means of single-crystal X-ray structure determination, NMR spectroscopy, IR spectroscopy, and mass spectrometry.

Theoretical study of structure, bonding, and electronic behavior of low-valent bismuth cyclopentadienyl and pentamethylcyclopentadienyl half-sandwich compounds.

The correlations between structural and electronic properties of the bismuth cyclopentadienyl complexes of the types [(C(5)R(5))(n)Bi(n)](q+) (where R = H, Me; n = 1, q = 2; n = 1-4, q = 0) and (C(5)R(5))BiX(2) (where R = H, Me; X = Cl, Br, I) were studied with quantum-chemical calculations. The influence of the ligand, significant variations in the Bi-C bond lengths, haptotropic shifts with distortion of the C(5)R(5) ring, Jahn-Teller splitting, interstabilization effects, and the role of the lone pairs on p-block element-unalkylated or peralkylated cyclopentadienyl ring interactions were examined to obtain qualitative and quantitative pictures of the intramolecular C(5)R(5)-Bi interactions. Our theoretical investigations of monovalent and trivalent bismuth cyclopentadienyl complexes give an insight into the geometric and electronic structures, the relative stabilities and further behavior of this kind of compounds.

2,2,6,6-tetramethylpiperidinogallium as a terminal and bridging ligand in homo- and heteroleptic chromium, nickel, and cobalt complexes.

By reaction of the gallium(I) derivative Ga(4)tmp(4) (tmp = 2,2,6,6-tetramethylpiperidino) with Cr(CO)(5)(cyclo-octene), Co(2)(CO)(8), and Ni(cyclooctadiene)(2), respectively, the Gatmp complexes [Cr(CO)(5)Gatmp], (CO)(3)Cr(mu(2)-Gatmp)(3)Cr(CO)(3), (CO)(3)Co(mu(2)-Gatmp)(2)Co(CO)(3), and (tmpGa)(2)Ni(mu(2)-Gatmp)(3)Ni(Gatmp)(2) were obtained. The latter are described as derivatives of the binuclear metal carbonyls Cr(2)(CO)(9), Co(2)(CO)(8), and Ni(2)(CO)(7), where some or all carbonyls are replaced by the amino gallylene group. All compounds are characterized by spectroscopy and crystal structure analysis. The change of the bonding situation from localized two-center gallium metal bonds in the chromium derivative to three-center bonds in the cobalt complex is discussed by means of density functional theory calculations.

Oxidation of diiron and triiron sulfurdithiolato complexes: mimics for the active site of [FeFe]-hydrogenase.

The oxidation of the hexacarbonyl(1,3-dithiolato-S,S')diiron complexes 4a-4c with varying amounts of dimethyldioxirane (DMD) was systematically studied. The chemoselectivity of the oxidation products depended upon the substituent R (R=H, Me, 1/2 (CH2)(5)). For R=H, four oxidation products, 6a-6d, have been obtained. In the case of R=Me, three products, 7a-7c, were formed, and for R=1/2 (CH2)(5), only complex 8 was observed. These observations are due to steric and electronic effects caused by the substituent R. Additionally, oxidation of the triiron complex 5 with DMD was performed to yield the products 9a and 9b. X-Ray diffraction analyses were performed for 6a-6d, 7a, and 7c, as well as for 9a and 9b. The electronic properties were determined by density-functional theory (DFT) calculations.

Synthesis and characterization of hydroxy-functionalized models for the active site in Fe-only-hydrogenases.

The reactions of DL-1,4-disulfanylbutane-2,3-diol and 1,3-disulfanylpropan-2-ol with dodecacarbonyltriiron have been investigated. As main products, the iron complexes 1 and 2 were isolated and characterized by spectroscopic methods, as well as single crystal X-ray analysis. Additionally, the unusually large bond angles in the dithiolato bridge was investigated via density-functional theory (DFT) calculations. Moreover, the electrochemical features have been studied by cyclic voltammetry.

Oxidative N-dealkylation in cobalt-bispidine-H2O2 systems.

The reaction of the Co(II) complex with the rigid bispidine ligand L1 with two tertiary amine and two pyridine donors, [Co(II)(L1)(OH2)2]2+, with H2O2 and O2 produces [Co(II)(L2)(OH2)2]3+, where L2 is demethylated at one of the amine donors, and CH2O.

Solid state characterization of oligopyridine dicarboxamide helicates.

A heptameric amide of 2,6-diaminopyridine and 2,6-pyridinedicarboxylic acid coordinates to Cu(II) to assemble into a double helical complex with a string of six shortly spaced Cu ions.

A Silatetragallane-Classical Heterobicyclopentane or closo-Polyhedron?

Classical and nonclassical can be used to describe the bonding in the polyhedral Ga4 Si framework of the silagallanate ion [Me3 SiSi{GaSi(SiMe3 )3 }3 GaSiMe3 ]- (the GaSi framework is depicted in the picture). This is the result of density functional calculations that were carried out on model compounds. The cluster was obtained by ultrasonication of gallium and iodine and subsequent reaction with (Me3 Si)3 Li(thf)3 .

Synthesis, structure and reactions of an amidinate stabilised trigallane.

The neutral trigallane R(3)Ga(3)I(2) was obtained in high yields by reaction of "GaI" with the moderately sterically demanding lithium N,N'-dicyclohexylneopentylamidinate. Its chemical reactions with N-lithio-2-propanimine, sodium superhydride and elemental iodine were investigated. RI-DFT calculations have been performed to confirm the bonding situation. All compounds are characterised by crystal structure analysis and NMR-spectroscopy.

Synthesis and structure of tri- and octaindium compounds.

The reactions of InCp* with alkali metal silanides M(thf)(n)SiRPh(2) (R = Me, Ph) resulted in the triindanate [(Ph(3)Si)(3)In-In-In(SiPh(3))](-) with a linear arrangement of In atoms and the octaindium clusters [(In(8)(SiPh(3))(8)](m-) (m = 0, 2) amongst others, which were characterized by X-ray crystallography. The neutral cluster has a bisphenoidal core similar to that of B(8)Cl(8), whilst the anionic one adopts a distorted square antiprismatic structure. In addition, the tri- and octaindium compounds were studied by DFT calculations.

Distortional isomerism with copper(I) complexes of 3,7-diazabicyclo[3.3.1]nonane derivatives.

Two structural forms of the tetradentate bispidine ligand (3,7-diazabicyclo[3.3.1]nonane, pyridine-substituted at C2 and C4), coordinated to CuI, are known: a pentacoordinate square pyramidal structure with an acetonitrile completing the coordination sphere, and a tetracoordinate distorted tetrahedral structure, where one of the pyridine groups is dissociated. Similar structures are observed in crystals of the CuI complexes of another tetradentate and two pentadentate bispidine ligands. The structural dynamics in the CuI coordination sphere of the four ligands are probed by 1H-NMR spectroscopy, supported by approximate density functional theory (DFT) calculations. DFT and NMR spectroscopy indicate that there is an additional isomeric form, and experimental as well as computational data lead to the conclusion that the potential energy surfaces are very flat with various shallow minima.