Synthesis and Characterization of Three Multi‐Shell Metalloid Gold Clusters Au32(R3P)12Cl8

Three multi‐shell metalloid gold clusters of the composition Au₃₂(R₃P)₁₂Cl₈ (R=Et, ⁿPr, ⁿBu) were synthesized in a straightforward fashion by reducing R₃PAuCl with NaBH₄ in ethanol. The Au₃₂ core comprises two shells, with the inner one constituting a tilted icosahedron and the outer one showing a distorted dodecahedral arrangement. The outer shell is completed by eight chloride atoms and twelve R₃P groups. The inner icosahedron shows bond lengths typical for elemental gold while the distances of the gold atoms in the dodecahedral arrangement are in the region of aurophilic interactions. Quantum‐chemical calculations illustrate that the Jahn–Teller effect observed within the cluster core can be attributed to the electronic shell filling. The easily reproducible synthesis, good solubility, and high yields of these clusters render them perfect starting points for further research.     

Structural Diversity of Metallosupramolecular Assemblies from Cu(phen)2+ (phen = 1,10‐Phenanthroline) Building Blocks and 4,4′‐Bipyridine

Attempts to crystal engineer metallosupramolecularcomplexes from Cu(phen)²⁺ building blocks and the prototypical,rod‐like, exo‐bidentate ligand 4,4′‐bipyridine (4,4′‐bipy) by layering techniques are described. Reactions of Cu(phen)²⁺ (phen = 1,10‐phenanthroline) with 4,4′‐bipy in the presence of NO₃^– counterions yielded two distinct, discrete, dinuclear, C_i symmetric, dumbbell‐typecomplexes, [{Cu(NO₃)₂(phen)}₂(4,4′‐bipy)] ( 1 ) and [{Cu(NO₃)(phen)(H₂O)}₂(4,4′‐bipy)](NO₃)₂ ( 2 ), depending upon the mixture of solvents used for crystallization. In compound 1 , a mono‐ and a bidentate nitrato group coordinate to Cu²⁺, whereas in 2 the monodentate nitrato groups are replaced by aqua ligands, which introduce additional hydrogen‐bond donor functionality to the molecule. The crystal structure of 1 was determined by single‐crystal X‐ray analysis at 296 and 110 K. Upon cooling, a disorder‐order transition occurs, with retention of the space group symmetry. The crystal structure of 2 at room temperature was reported previously [Z.‐X. Du, J.‐X. Li, Acta Cryst. 2007 , E63, m2282]. We have redetermined the crystal structure of 2 at 100 K. A phase transition is not observed for 2 , but the low temperature single‐crystal structure determination is of significantly higher precision than the room temperature study. Both 1 and 2 are obtained phase‐pure, as proven by powder X‐ray diffraction of the bulk materials. Crystals of [Cu(phen)(CF₃SO₃)₂(4,4′‐bipy) · 0.5H₂O]_n ( 3 ), a one‐dimensional coordination polymer, were obtained from [Cu(CF₃SO₃)₂(phen)(H₂O)₂] and 4,4′‐bipy. In 3 , Cu(phen)²⁺ corner units are joined by 4,4′‐bipy via the two vacant cis sites to form polymeric zig‐zag chains, which are tightly packed in the crystal. Compounds 1 – 3 were further studied by infrared spectroscopy.     

Unusual Oligonuclear Copper(II) Complexes based on a Bis( tridentate) Compartmental Pyrazolate Ligand

Some unusual oligonuclear copper(II) complexes with a bis(tridentate) pyrazolate‐based ligand that is composed of two diethylentriame‐type coordination compartments have been structurally characterized. In [(LCu₂)₂(CO₃)(H₂O)₂(ClO₄)](ClO₄)₃ ( 1 ), CO₂ has been taken up and two {LCu₂} subunits are spanned by both a μ₃‐μ₃‐κO:κO′:κO″‐bridging carbonate as well as by a μ₃‐κO:κO′:κO″‐bridging perchlorate. The latter is a rare structural motif in coordination chemistry. In one experiment, a different complex [(LCu₂(OH))₂Cu₂(OH)₄](BF₄)₄ ( 2 ) has been serendipitiously obtained. One Cu atom of each {LCu₂} subunit of 2 together with two further copper ions forms a pyrazolate‐appanded {Cu₄(OH)₄} cube.     

Distortions of π‐Coordinated Arenes with Anionic Character

A qualitative analysis of the distortions that operate on the π system of bridging arenes with anionic character is presented and substantiated by computational studies at the density functional B3LYP and CASSCF levels. The observed effects of bonding to two metal atoms and of the negative charge are an expansion of the arene ring due to the partial occupation of π* orbitals, an elongation or compression distortion accompanied by a loss of the equivalence of carbon‐carbon bonds due to a Jahn–Teller distortion of the arene dianions, and a ring puckering due to a second‐order Jahn–Teller distortion that may appear independently of the existence of the first‐order effect. The workings of the orbital mixing produced by these distortions have been revealed in a straightforward way by a pseudosymmetry analysis of the HOMOs of the distorted conformations. The systems studied include Li^I and Y^III adducts of benzene, as well as trimethylsilyl‐substituted derivatives in the former case. An analysis of the structural data of a variety of purported di‐ and tetraanionic arene ligands coordinated to transition metals in several bridging modes has reproduced the main geometrical trends found in the computational study for the benzene and trimethylsilyl‐substituted benzene dianions, allowing a classification of the variety of structural motifs found in the literature.     

A comparison of ground- and excited-state properties of [Ru(bz)2]2+ and bis(η6-benzene)ruthenium(II) p-toluenesulfonate using the density functional theory

The ground- and excited-state properties of both [Ru(bz)₂]²⁺ and crystalline bis(η⁶-benzene)ruthenium(II) p-toluenesulfonate are investigated using the density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet structure splitting of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between the [Ru(bz)₂]²⁺ system and its first shell of neighbor molecules. The overall agreement between experimental and calculated ground- and excited-state properties is good, as far as the absolute transition energies, the Stokes shift, and the geometry of the excited states are concerned. The calculated d-d excitation energies of the isolated cluster are typically 1000–2000 cm⁻¹ too low. An energy lowering is obtained in a_1g→e_1g(³E_1g) excited state when the geometry of [Ru(bz)₂]²⁺ is bent along the e_1u Renner–Teller active coordinate. It vanishes as the crystal packing is taken into account. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1343–1353, 1999     

Structural Effects of Cu/Zn Substitution in the Malachite–Rosasite System

Synthetic zincian malachite samples (Cu_1–xZn_x)₂(OH)₂CO₃ with x = 0, 0.1, 0.2 and 0.3 were characterized by powder X‐ray diffraction and optical spectroscopy. The XRD patterns of the samples up to x = 0.2 indicate single phase materials with an approximately linear dependence of the refined lattice parameters on the zinc content. In contrast, the sample with a nominal zinc content x = 0.3 shows the formation of a small amount of aurichalcite (Zn,Cu)₅(OH)₆(CO₃)₂ as an additional phase. Based on the lattice parameter variations, the zinc content of the zincian malachite component in this sample is estimated to be x ≈? 0.27, which seems to represent the maximum possible substitution in zincian malachite under the synthesis conditions applied. The results are discussed in relation to preparation of Cu/ZnO catalysts and the crystal structures of the minerals malachite and rosasite. One striking difference between these two structurally closely related phases is the orientation of the Jahn–Teller elongated axes of the CuO₆ octahedra in the unit cell, which seems to be correlated with the placement of the monoclinic β angle. The structural and chemical relationship between these crystallographically distinct phases is discussed using a hypothetical intermediate Zn₂(OH)₂CO₃ phase of higher orthorhombic symmetry. In addition to the crystallographic analysis, optical spectroscopy proves to be a useful tool for estimation of the Cu:Zn ratio in (Cu_1–xZn_x)₂(OH)₂CO₃ samples.     

Simplest proof of the Jahn–Teller theorem for molecular systems

A new simple proof of the Jahn–Teller theorem for molecular systems is presented. The proof is based on some general properties of symmetric square representation characters that simplify their explicit treatment and minimize the use of tables. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

O,N‐Chelated Vanadium(IV) Oxo Aminophenolate Complexes: the Effect of Steric Bulk on the Vanadium Coordination Geometry. Can this Influence be detected Spectroscopically?

In order to study the effect of steric bulk on the vanadium coordination geometry in O, N‐chelated vanadium oxo (bis)phenolates, six different ortho‐aminophenolate ligands have been used. The ortho‐aminophenolate system was changed at three different places, i.e. 1) the second ortho position (C⁶) of the arene ring (R), 2) the substituents at the amino nitrogen (R′ and R″), and 3) the benzylic carbon atom (R*). The phenols were used in the preparation of the vanadium oxo (bis)phenolate complexes. In order to study whether it is possible to predict geometrical features of these vanadium complexes, UV/Vis, solution and frozen state EPR and ¹⁴N ESEEM spectroscopic data was measured and compared to the structural features of four structurally characterized vanadium oxo (bis)phenolates. Unfortunately, it turned out that is was not possible to correlate the EPR parameters, the UV/Vis HOMO‐LUMO transitions or ¹⁴N hyperfine couplings to the structural parameters.     

Large magnetic anisotropy in pentacoordinate Ni(II) complexes

Pentacoordinate complexes in which Ni(II) is chelated by the tridentate macrocyclic ligand 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPrtacn) of formula [Ni(iPrtacn)X(2)] (X=Cl, Br, NCS) have relatively large magnetic anisotropies, revealed by the large zero-field splitting (zfs) axial parameters |D| of around 15 cm(-1) measured by frequency-domain magnetic resonance spectroscopy (FDMRS) and high-field high-frequency electron paramagnetic resonance (HF-HFEPR). The spin Hamiltonian parameters for the three complexes were determined by analyzing the FDMRS spectra at different temperatures in zero applied magnetic field in an energy window between 0 and 40 cm(-1). The same parameters were determined from analysis of HF-HFEPR data measured at different frequencies (285, 380, and 475 GHz) and at 7 and 17 K. The spin Hamiltonian parameters D (axial) and E (rhombic) were calculated for the three complexes in the framework of the angular overlap model (AOM). The nature and magnitude of the magnetic anisotropy of the three complexes and the origin of the influence of the X atoms were analyzed by performing systematic calculations on model complexes.     

Syntheses and coordination chemistry of methylpyridylphosphine oxide ligands with copper(II)

The coordination properties of three heterofunctional phosphine oxide ligands, 2-methylpyridyldiphenylphosphine oxide (L1), phenylphosphino-bis-2-methylpyridine oxide (L2) and phenylphosphino-bis-2-methylpyridine N,N′,P-trioxide (L3) with Cu(II) is described. The X-ray crystal structures of the compounds display a distorted octahedral geometry, which exhibit Jahn–Teller distortions. In compounds 1 and 2, the L1 and L2 ligands react with Cu(BF₄)₂ in a 2:1 ligand to metal ratio, respectively, with the BF₄ anions interacting with the metal center. L3 reacts with Cu(BF₄)₂ in 1:1 and 2:1 ligand/metal ratios to form compounds 3 and 4, respectively. Addition of either 2,2′-bipyridine or 4,4′-bipyridine to reaction solutions containing Cu(BF₄)₂ and L3 produces a discrete molecule (5) and a polymeric structure (7), respectively. The reaction of both bipyridines in the presence of Cu(BF₄)₂ and L3 gives rise to a discrete molecule (6) characterized by two octahedral coppers interconnected by the 4,4′-bipyridine. The electrochemical and photophysical properties of all compounds were investigated by cyclic voltammetry (CV) and UV–Vis, as they exhibited no emission or excitation in fluorimetric experiments.     

Unraveling the Coordination Geometry of Copper(II) Ions in Aqueous Solution through Absorption Intensity

Strong colors: The solvation structure of copper(II) ions in water can be determined by optical absorption spectroscopy. Focus is placed on the absorption intensity (green: Cs(2) Cu(SO(4) )(2) ?6?H(2) O, black: CuSO(4) ?5?H(2) O, red: Cu(2+) in aqueous solution, and blue: Cu(2+) in glass). A dynamical model based on a Jahn-Teller-distorted complex describes the coordination of copper(II) ions in hydrate crystals and aqueous solution.     

Synthesis and Characterization of Tris(oxazolinyl)borato Copper(II) and Copper(I) Complexes

The reaction of To^MTl (To^M=tris(4,4-dimethyl-2-oxazolinyl)phenylborate) and CuBr₂ in benzene at 60 °C provides To^MCuBr ( 1 ) as an entry-point into tris(oxazolinyl)phenylborato copper chemistry. To^MCuO^tBu ( 2 ) and To^MCuOAc ( 3 ) are prepared by the reactions of To^MCuBr with KO^tBu and NaOAc, respectively. To^MCuO^tBu is transformed into (To^MCuOH)₂ ( 4 ) through hydrolysis. NMR, FT-IR, and EPR spectroscopies are used to determine the electronic and structural properties of these copper(II) compounds, and the solid-state structures were characterized by X-ray crystallography. Reduction of copper is observed upon treatment of To^MCuO^tBu with phenylsilane in an attempt to synthesize monomeric copper(II) hydride. To^MCu ( 5 ) and To^M₂Cu ( 6 ) were independently synthesized and characterized for comparison.     

Einfluss von H‐Brückenbindungen auf die Jahn–Teller‐Verzerrung in den Kettenstrukturen von 2,2′‐bipyMn(H2PO4)F2·H2O und 2,2′‐bipyMn(H2PO4)2F

In the system 2,2′‐bipyridine/Mn^III/HF/H₃PO₄/H₂O two compounds with chain structures could be prepared and characterised by X‐ray structure analyses. 2,2′‐bipyMn(H₂PO₄)F₂·H₂O ( 1 ): monoclinic, twinned, space group P2₁/c, Z = 4, a = 6.7883(4), b = 10.9147(5), c = 17.8102(8) Å, β = 100.142(4)°, R = 0.0328. 2,2′‐bipyMn(H₂PO₄)₂F ( 2 ): triclinic, space group P , Z = 2, a = 6.675(1), b = 10.715(1), c = 11.013(1) Å, α = 107.595(9)°, β = 90.994(9)°, γ = 95.784(8)°, R = 0.0252. Both compounds show chain structures with trans‐bridging dihydrogenphosphate ligands and bipy and two fluorine ligands for ( 1 ), or bipy, fluorine and an additional dihydrogenphosphate, respectively, for ( 2 ) in equatorial positions. Due to the pseudo‐Jahn–Teller effect, Mn^III shows elongated octahedral coordination with ferrodistortive ordering along the chain direction. The distortion is remarkably higher in ( 1 ) than in ( 2 ). This is discussed in context with additional hydrogen bonds along the chain in ( 2 ).     

Cis‐trans Isomerism in Copper(II) Complexes with N‐acyl Thiourea Ligands

The N‐acyl thiourea complexes bis[N,N‐diethyl‐N′‐(p‐nitrobenzoyl)‐thioureato]copper(II) ( 1a,1b ) and bis(N,N‐diphenyl‐N′‐benzoylthioureato)copper(II) ( 2a,2b ) crystallize in each case in two modifications. X‐ray structural analysis shows that 1a and 1b are cis‐trans isomers. This is very unusual for N‐acyl thioureato complexes because with exception of one platinum(II) complex up to now only cis complexes have been found. In contrast X‐ray structural analysis of both forms 2a and 2b of the other complex shows no cis‐trans pair. Both modifications are cis complexes. In solution both isomers of the copper(II) complexes are observable by EPR spectroscopy.     

Calixarene-Based Copper(I) Complexes as Models for Monocopper Sites in Enzymes

A cavity that acts as a molecular funnel is formed from calix[6]arene 1 and [Cu^I(NCCH₃)₄]PF₆ [Eq. (a)]. An exchange of the well-protected acetonitrile ligand for other nitriles RCN is only possible with small R groups. The protection of the copper ions precludes oxidative dimerization; thus, the complexes mimic the mononuclear site of copper enzymes.     

EPR Spectra of Copper(II) Complexes with N,N-Dialkyl Amino Acids. The Influence of Water dissolved in Organic Solvents on the Copper(II) Coordination Sphere

EPR spectra of four bis(N,N-dialkyl-L-α-aminoacidato) copper(II) complexes were studied with the aim to determine the effect of the water molecules dissolved in organic solvents on the electronic states of copper(II). It was shown that water dissolved in methylene chloride or dioxan influence the copper(II) electronic states. If the amino acid side chains are long enough to form the aliphatic intramolecular van der Waals contacts, the water molecules will induce the change in the conformation of the whole complex.     

Synchronizing Steric and Electronic Effects in {RuII(NNNN,P)} Complexes: The Catalytic Dehydrative Alkylation of Anilines by Using Alcohols as a Case Study

A series of new hexacoordinated {Ru^II(NNNN,P)} complexes was prepared from [RuCl₂(R₃P)₃]. Their structure was determined by X‐ray crystallography. The catalytic potential of this new class of complexes was tested in the alkylation of aniline with benzyl alcohol. In this test reaction, the influence of the counteranion plus electronic influences at the tetradentate ligand and the phosphine ligand were examined. The electrochemistry of all complexes was studied by cyclic voltammetry. Depending on the substituent at the ligand backbone, the complexes showed a different behavior. For all N‐benzyl substituted complexes, reversible Ru^II/III redox potentials were observed, whereas the N‐methyl substituted complex possessed an irreversible oxidation event at small scan rates. Furthermore, the electronic influence of different substituents at the ligand scaffold and at the phosphine on the Ru^II/III redox potential was investigated. The measured E₀ values were correlated to the theoretically determined HOMO energies of the complexes. In addition, these HOMO energies correlated well with the reactivity of the single complexes in the alkylation of aniline with benzyl alcohol. The exact balance of redox potential and reactivity appears to be crucial for synchronizing the multiple hydrogen‐transfer events. The optimized catalyst structure was applied in a screening on scope and limitation in the catalytic dehydrative alkylation of anilines by using alcohols.     

Manganese(III) Formate: A Three-Dimensional Framework That Traps Carbon Dioxide Molecules

Carbon dioxide, formic acid, and water molecules are trapped in the crystal lattice of manganese(III ) formate (see 1 ), which was obtained by reducing permanganate with formic acid. Each CO₂ guest molecule exhibits four C−H⋅⋅⋅O−C−O interactions with the three-dimensional host framework of Mn(HCOO)₃ units. Compound 1 undergoes an antiferromagnetic phase transition at 27 K.