Interactions In Transition Metal Complexes Research Articles

Azido-mediated intermolecular interactions of transition metal complexes.

The coordinated azido ligand has a variety of ways to establish intermolecular contacts whose nature is computationally analysed in this work on dimers of the [N3-Hg(CF3)] complex with different interactions involving only N⋯N contacts, or with an additional Hg⋯N contact. The applied tools include the molecular electrostatic map of the monomer, an energy decomposition analysis (EDA), a topological AIM analysis of the electron density and the study of NCI (non-covalent interactions) isosurfaces. The interactions between two azido ligands are found to be weakly stabilizing (by 0.2 to 2.7 kcal mol-1), topology-dependent and require dispersion forces to complement orbital and electrostatic stabilization. Those interactions are supplemented by the formation of simultaneous Hg⋯N secondary interactions by about -1 kcal mol-1, and by the ability of the monomer to simultaneously interact with several neighbours in the crystal structure.

Synthesis, characterization, DFT, In-vitro anti-microbial, cytotoxicity evaluation, and DNA binding interactions of transition metal complexes of quinoxaline Schiff base ligand

A series of Cr(III), Mn(II), Fe(III), Co(II), Cu(II) and Ni(II) transition metal complexes of the quinoxaline based Schiff base ligand were synthesized and characterized on the basis of analytical, conductance, magnetic moment, FT-IR, NMR, ESR, EDAX and electronic spectral data. The ligand behaves as bidentate OO donors through phenolic oxygen and carbonyl oxygen in the quinoxaline ring. The molecular structure of the quinoxaline Schiff base ligand and Cu(II) complex was investigated theoretically. The optimized molecular structure was obtained from Gaussian 09 program. The antimicrobial activity of the ligand and the complexes were screened for various bacterial and fungal strains and found to be good for Co(II) and Mn(II) complexes and moderate for the other synthesized complexes. The minimum inhibitory concentration of the Co(II) and Mn(II)complexes against S. aureus, S. paratyphi and A. niger were found to be 250 μg/ml, 125 μg/ml, 500 μg/ml and 250 μg/ml, 250 μg/ml , 500 μg/ml respectively. The anti-cancer activity of the ligand and the complexes were studied against the human breast cancer cell lines MCF-7 and found to be good for Cu(II), Co(II) and Mn(II) complexes. The in-vitro anti-oxidant activities of the complexes and found to be moderate for all complexes. The DNA binding ability of the complexes were checked and their binding constants were reported using absorption and emission spectral studies.

Intermolecular Carbonyl···Carbonyl Interactions in Transition-Metal Complexes.

We performed a comprehensive analysis of intermolecular carbonyl-carbonyl interactions in transition-metal complexes. Those interactions can be classified in two main types depending on the organometallic or organic nature of the donor carbonyl: M-CO···CO and R-CO···CO, respectively. By means of a combined structural and computational study we unraveled their geometrical features and strength. Moreover, electronic structure, natural bond orbitals, energy decomposition analysis, and quantum theory of atoms in molecules calculations were performed to try to understand their nature. Remarkably, we discovered that these carbonyl-carbonyl contacts have several features of the n → π* interaction. The charge transfer from an oxygen lone pair to an empty antibonding π orbital of the acceptor carbonyl is also accompanied by an electrostatic Oδ-···Cδ+ interaction. To the best of our knowledge this is the first report of an intermolecular n → π* interaction in metal complexes. These results might be significant, for instance, for the catalytic activation of carbonyl-containing small molecules with metal compounds or in the design of hybrid organic-inorganic materials, metal-organic frameworks, and other extended structures.

The n → π* interaction in metal complexes

We report here, for the first time, the existence of n →π* interactions in transition metal complexes containing carbonyl ligands. This interaction has been observed to be surprisingly abundant and to stabilize precise molecular conformations that maximize the overlap between the donor and acceptor orbitals.

Luminescent Rhenium(I) and Iridium(III) Polypyridine Complexes as Biological Probes, Imaging Reagents, and Photocytotoxic Agents.

Although the interactions of transition metal complexes with biological molecules have been extensively studied, the use of luminescent transition metal complexes as intracellular sensors and bioimaging reagents has not been a focus of research until recently. The main advantages of luminescent transition metal complexes are their high photostability, long-lived phosphorescence that allows time-resolved detection, and large Stokes shifts that can minimize the possible self-quenching effect. Also, by the use of transition metal complexes, the degree of cellular uptake can be readily determined using inductively coupled plasma mass spectrometry. For more than a decade, we have been interested in the development of luminescent transition metal complexes as covalent labels and noncovalent probes for biological molecules. We argue that many transition metal polypyridine complexes display triplet charge transfer ((3)CT) emission that is highly sensitive to the local environment of the complexes. Hence, the biological labeling and binding interactions can be readily reflected by changes in the photophysical properties of the complexes. In this laboratory, we have modified luminescent tricarbonylrhenium(I) and bis-cyclometalated iridium(III) polypyridine complexes of general formula [Re(bpy-R(1))(CO)3(py-R(2))](+) and [Ir(ppy-R(3))2(bpy-R(4))](+), respectively, with reactive functional groups and used them to label the amine and sulfhydryl groups of biomolecules such as oligonucleotides, amino acids, peptides, and proteins. Additionally, using a range of biological substrates such as biotin, estradiol, and indole, we have designed luminescent rhenium(I) and iridium(III) polypyridine complexes as noncovalent probes for biological receptors. The interesting results generated from these studies have prompted us to investigate the possible applications of luminescent transition metal complexes in intracellular systems. Thus, in the past few years, we have developed an interest in the cytotoxic activity, cellular uptake, and bioimaging applications of these complexes. Additionally, we and other research groups have demonstrated that many transition metal complexes have facile cellular uptake and organelle-localization properties and that their cytotoxic activity can be readily controlled. For example, complexes that can target the nucleus, nucleolus, mitochondria, lysosomes, endoplasmic reticulum, and Golgi apparatus have been identified. We anticipate that this selective localization property can be utilized in the development of intracellular sensors and bioimaging reagents. Thus, we have functionalized luminescent rhenium(I) and iridium(III) polypyridine complexes with various pendants, including molecule-binding moieties, sugar molecules, bioorthogonal functional groups, and polymeric chains such as poly(ethylene glycol) and polyethylenimine, and examined their potentials as biological reagents. This Account describes our design of luminescent rhenium(I) and iridium(III) polypyridine complexes and explains how they can serve as a new generation of biological reagents for diagnostic and therapeutic applications.

Procedure for the analysis of interfragment donor-acceptor interactions in transition metal complexes

The procedure based on the first order density matrix has been suggested for the description of molecular electronic structures. The procedure includes: The calculation of interatomic bond-order indices and their σ-, π-, and δ-components; the construction of multicenter orbitals localized on fragments responsible for the formation of bonds inside fragments and between fragments; the classification of the constructed orbitals according to their population, valence activity, and orientation; the characterization of the realized donoracceptor abilities of the fragments (ligands and more complicated structural units). The interaction between fragments is described by a rather small number of multicenter orbitals localized on them. The concept of the valence activity of a polyatomic fragment has been introduced and the algorithm of its calculation has been offered. The procedure is illustrated by the analysis of electronic structures of ruthenium(II), platinum(II), and rhodium(I) complexes.

Directed secondary interactions in transition metal complexes of tripodal pyrrole imine and amide ligands

Tripodal pyrrole imine and amide ligands provide platforms for combined primary and secondary coordination sphere interactions in square planar Pd and Cu, and octahedral Ti complexes.

Intramolecular MLOH/π and MLNH/π interactions in crystal structures of metal complexes

AbstractIntramolecular metal-ligand OH/π (MLOH/π) and metal-ligand NH/π (MLNH/π) interactions in transition metal complexes between aqua or ammine ligand and ligand containing a C6-aromatic ring were investigated in crystal structures deposited in the Cambridge Structural Database (CSD). These intramolecular interactions appear in 38 structures with aqua ligand as the hydrogen atom donor and in 10 structures with ammine ligand as the hydrogen atom donor. Among all these complexes only one is negatively charged, 14 are positively charged and 33 are neutral indicating that the overall charge of the molecule has an influence on the XH/π (X = O or N) interactions. Energy estimated by DFT calculations is approximately 19 kJ mol−1 for the MLOH/π interactions and approximately 15 kJ mol−1 for the MLNH/π interactions.

Very strong metal ligand aromatic cation-π interactions in transition metal complexes: intermolecular interaction in tetraphenylborate salts

Strong intermolecular interactions between ligands in cationic metal complexes and aromatic rings of tetraphenylborate anion, so-called metal ligand aromatic cation-π (MLACπ) interactions, were found by screening Cambridge Structural Database. Distances between phenyl ring and ligand are shorter in these structures than in previously reported MLACπ interactions by 0.2 Å.

Intramolecular C−H···π Interactions in Metal-Porphyrin Complexes

Cambridge Structural Database (CSD) was screened in order to find intramolecular C−H···π interactions with a chelate ring of coordinated porphyrin. It was found 154 crystal structures with 244 intramolecular C−H···π interactions in transition metal complexes with derivatives of porphyrin. Comparison of interacting distances indicates that interactions of hydrogen atoms in positions 2 and 6 of axially coordinated pyridine are more favorable with ruffled than with planar porphyrin.

A pyracylene model for the interaction of transition metals with fullerenes: a density functional study

Pyracylene, a polynuclear aromatic hydrocarbon which is made up of two benzene and two cyclopentadienyl rings, has been employed as a model to study the interaction of transition metal complexes with fullerenes. To reproduce adequately the geometric and electronic structure of fullerene with a pyracylene model, we had to impose suitable geometric constraints forcing the pyramidalisation angle on the two central carbon atoms to assume a value similar to that observed in C60. Density functional calculations were then performed on (PH3)2M(C14H8) (M = Ni, Pd, Pt) molecules. The results have been analysed in terms of the Chatt–Dewar–Duncanson model and show that the constrained pyracylene is a fairly good model to study the interaction of transition metals with fullerene: geometries are reproduced within 0.02 A and the bond dissociation energies are slightly underestimated by only 10–40 kJ mol−1.

Hyperfine Coupling and Magnetic Interaction of Layer-Structured Compound Ni(OD) 2 Studied by Solid-State High-Resolution Deuterium NMR

Magnetic interaction and hyperfine coupling were investigated for Ni(OD) 2 as a reference of our series of studies of layer-structured Cu(II) assembled complexes. In crystal of Ni(OD) 2 , Ni(II) ions with S = 1 are bridged by hydroxyl ions to form an equilateral planer triangular lattice. Hyperfine coupling constant of deuterium of hydroxyl ions was determined to be −0.17 MHz from temperature dependence of isotropic shift of a magic angle spinning deuterium NMR spectrum. Ferromagnetic exchange interaction J the layer was estimated to be +3 K from the deuterium NMR shift by assuming Heisenberg model for planer triangular lattice. Present results indicated that magic angle spinning deuterium NMR is also useful to determine magnetic local structure and magnetic interaction of transition metal complexes with electron spins greater than S = 1/2.

Intramolecular Metal Ligand Aromatic Cation−π Interactions in Crystal Structures of Transition Metal Complexes

Cation−π interactions between ligands coordinated to a metal cation and aromatic groups have been predicted by theoretical calculations, and have been found in crystal structures of metalloproteins from the Protein Data Bank (PDB). We proposed metal ligand aromatic cation−π (MLACπ) interaction as intramolecular interactions in transition metal complexes. Searching crystal structures of transition metal complexes from the Cambridge Structural Database (CSD) reveals that there are quite a number of metal complexes, where an aromatic ring interacts with a hydrogen atom from a ligand in the same complex. The hydrogen atom is separated from the metal center by a few bonds and gains positive charge from the metal atom. In the complexes there are various metal atoms and various ligands. In the most of the complexes, the aromatic ring is separated from the metal center by two or four bonds, and interacts with the hydrogen atom of another ligand. In complexes where the aromatic ring is separated from the metal center by four or five bonds, there are examples of aromatic groups interacting with the hydrogen atom in the same ligand. By quantum chemical computations it was evaluated for the model systems of cationic cobalt(III) complexes with a charge of +1, that the energy of this intramolecular MLACπ interaction is about 4 kcal/mol.

Interaction of metallopyrazoliumylporphyrins with calf thymus DNA.

The interaction of transition metal complexes of cationic porphyrins bearing five membered rings, meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (MPzP, M=Mn(III), Ni(II), Cu(II) or Zn(II)), with calf thymus DNA (ctDNA) has been studied. Metalloporphyrins NiPzP and CuPzP are intercalated into the 5'GC3' step of ctDNA. MnPzP is bound edge-on at the 5'TA3' step of the minor groove of ctDNA, while ZnPzP is bound face-on at the 5'TA3' step of the major groove of ctDNA. The binding constants of the metalloporphyrins to ctDNA range from 1.05x10(5) to 2.66x10(6) M(-1) and are comparable to those of other reported cationic porphyrins. The binding process of the metallopyrazoliumylporphyrins to ctDNA is endothermic and entropically driven. These results have revealed that the kind of central metal ions of metalloporphyrins influences the binding characteristics of the porphyrin to DNA.

Spin Coupling Interactions in Transition Metal Complexes Containing Radical o-Semiquinone Ligands. A Review

Transition metal complexes ofo-semiquinone (SQ) ligands have been studied extensively over the past 25 years. A particularly interesting aspect of this coordination chemistry concerns magnetic interactions between paramagnetic metal ions and the radical anionic ligands. In this review we begin with a survey of relatively simple complexes consisting of a paramagnetic metal ion chelated by a single SQ ligand. Recent studies have revealed the importance of SQ-SQ coupling through diamagnetic metals, and complexes of this class are described in the second section of the review. Both interactions combine to account for the often complicated magnetic properties of complexes containing multiple SQ ligands chelated to a paramagnetic metal ion. Research on these complexes is surveyed in the third section with a concluding look toward polymeric SQ complexes. A review with 51 references.

Core correlation effects in weak interactions involving transition metal atoms

In our calculations of weak interactions in transition metal complexes some rather unusual contributions due to excitations from relatively inert subvalence electronic shells have been observed for copper interacting with water and ammonia. These contributions are analyzed in terms of cluster amplitudes which indicate that the copper–molecule interaction considerably increases the near degeneracy of atomic states. The t1 amplitude associated with the 3d→4s excitation rapidly increases with the decrease of the copper–molecule distance. This, in consequence, leads to the increasing role of the 3p shell polarization. This effect is essentially absent in the case of silver complexes.

Intra- and inter-molecular ferromagnetic interaction of transition metal complexes containing pyrimidine or pyrazine derivatives

The 1 2 spins of oxovanadium(IV) ions were ferromagnetically coupled with J k B = +1.1∼+2.7 K in the dinuclear complexes L[VO(hfac) 2] 2 (hfac = hexafluoroacetylacetonate, L = pyrimidine derivatives). Among them, a ferromagnetic transition was observed at about 0.14 K in PM[VO(hfac) 2] 2 (PM = pyrimidine). The polymeric complex QZ[Cu(hfac) 2] (QZ = quinazoline) gave a positive Weiss constant (+0.39 K). The ferromagnetic transition was observed at about 0.12 K.

Phase Transition Induced Motional Averaging of Hyperfine Interaction of Transition Metal Complexes in Molecular Solids

Abstract A reduction of the anisotropic hyperfine interaction of dopant transition metal complexes due to motional averaging is observed during order-disorder phase transitions in molecular solids. The onset of the reduction of the hyperfine splitting of copper benzoyl acetonate doped into hexamethyl benzene and cyclohexane corresponds to temperatures at which other data show evidence for order-disorder phase transitions. It is shown that this effect can be used to study the dynamics of the disordering. The approach is used to present evidence for the existence of new order-disorder phase transitions above room temperature in ammonium dihydrogen phosphate and potassium dihydrogen phosphate. Evidence for molecular tumbling is also found in the solid state of the liquid crystal material p-methoxy cinnamic acid.

Cooperative effect of dπ-electron delocalization in, and H...π type interaction of transition metal complexes with protic solvents

Abstract

High pressure reactor and cell for electronic and infrared spectral studies

An easily constructed, simply operated, high pressure reactor and ultraviolet-visible/infrared cell is described. The apparatus is designed for spectral studies of the interaction of transition metal complexes and small gaseous molecules in the liquid phase.Elevated pressures of the reacting gases are limited to those obtained with commercial bottled gases. An example of the utility of the apparatus is provided in the detection of an unstable ti(III) carbonyl, TiCl 3(CO)(PEt 3) 2, by high pressure infrared spectroscopy.