Analysis of the supramolecular structures of Sb(III) and Sb(V) catecholate complexes from the viewpoint of ligand solid angles

The ligand solid angle approach has been successfully applied to the analysis of the catecholate complexes of Sb(III) and Sb(V). The Sb(III) complexes possess an electron lone pair that influences their molecular structure but does not behave as a classic “ligand” when intermolecular interactions are concerned. The Sb(III) complexes in solid state form numerous intermolecular interactions that effectively increase metal shielding, and herein we analyze the effects of the lone pair of electrons on the complex coordination geometry. In the five-coordinate R₃CatSb(V) complexes (Cat = catecholate ligand, R = Ph, Me, Cl) the metal is shielded by 87(3)% and multiple intermolecular contacts are observed. The central metal in the six-coordinate antimony(V) complexes R₃CatSb(V) · L is shielded to the extent of 89(2)% and no strong attractive intermolecular interactions are detected in solid state. Thus, the metal shielding in excess of 85% is required to prevent complex dimerization or additional ligation of the central atom by a nucleophile.     

Advances in the coordination chemistry of nitrogen ligand complexes of coinage metals

Coinage metals nitrogen chemistry has not been studied extensively until recently. The focus of this review is the base- and halide-free complexes of the monoanionic nitrogen ligands. This review describes how minor ligand modifications can result in a drastic change in the metal–metal interactions in multinuclear compounds. Crystal structures of these complexes show individual complexes, dimers, supramolecular columnar packing or more complex supramolecular aggregates. Bulky substituents on the ligands can prevent intermolecular metal–metal interactions or the formation of supramolecular architectures. The nuclearity and metal–metal interactions in these complexes are controlled by ligand steric and electronic factors and solvent of crystallization. Many classes of nitrogen ligand coordination compounds have given rise to advances in several fundamental and applied research aspects. Recent potential applications of nitrogen ligand complexes are highlighted particularly for those complexes included in this review.     

Steric, electronic, and secondary effects on the coordination chemistry of ionic phosphine ligands and the catalytic behavior of their metal complexes

The effects of introducing ionic functionalities in phosphine ligands on the coordination chemistry of these ligands and the catalytic behavior of the corresponding metal complexes are reviewed. The steric and electronic consequences of such functionalizations are discussed. Apart from these steric and electronic effects, the presence of charged groups often leads to additional, supramolecular interactions that occur in the second coordination sphere of the metal complex, such as intramolecular, interligand hydrogen bonding and Coulombic repulsion. These interactions can significantly alter the behavior of the phosphine ligand in question. Such effects have been observed in phosphine-metal association/dissociation equilibria, ligand substitution reactions, and stereoisomerism in phosphine-metal complexes. By drawing general conclusions, this review offers an insight into the coordination and catalytic behavior of phosphine ligands containing ionic functionalities and their corresponding metal complexes.     

Bonding in Diborane–Metal Complexes: A Quantum‐Chemical and Experimental Study of Complexes Featuring Early and Late Transition Metals

The coordination chemistry of the doubly base‐stabilised diborane(4), [HB(hpp)]₂ (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido‐[1,2‐a]pyrimidinate), was extended by the synthesis of new late transition‐metal complexes containing Cu^I and Rh^I fragments. A detailed experimental study was conducted and quantum‐chemical calculations on the metal–ligand bonding interactions for [HB(hpp)]₂ complexes of Group 6, 9, 11 and 12 metals revealed the dominant B? H? M interactions in the case of early transition‐metal fragments, whereas the B? B? M bonding prevails in the case of the late d‐block compounds. These findings support the experimental results as reflected by the IR and NMR spectroscopic parameters of the investigated compounds. DFT calculations on [MeB(hpp)]₂ and model reactions between [B₂H₄ ? 2NMe₃] and [Rh(μ‐Cl)(C₂H₄)₂] showed that the bicyclic guanidinate allows in principle for an oxidative addition of the B? B bond. However, the formation of σ‐complexes is thermodynamically favoured. The results point to the selective B? H or B? B bond‐activation of diborane compounds by complexation, depending on the chosen transition‐metal fragment.     

An improved method for the computation of ligand steric effects based on solid angles

An improved algorithm has been designed to characterize ligand interactions in organometallic and coordination complexes in terms of the percentage of the metal coordination sphere shielded by a given ligand. The computations for ligand solid angles are performed numerically and employ introduced atomic radii that are larger than covalent but smaller than van der Waals radii. This approach enables facile evaluation of steric congestion in the metal coordination sphere, quantification of unfavorable interligand contacts, and in some cases prediction of the complex composition or ligand coordination on purely geometrical grounds.     

Polymerization catalysis with transition metal amidinate and related complexes

Applications of transition metal amidinate [RC(NR′)₂], guanidinate and amidopyridine complexes to olefin coordination polymerization are reviewed. In addition, the use of complexes, featuring closely related ligands, such as phosphonamide or iminophosphonamide [R₂P(NR′)₂], in olefin polymerization is highlighted. Some of these complexes have also been investigated in the stereoregular polymerization of styrene and conjugated dienes, whereas more recent work has focused on controlled ring-opening polymerization of lactones and lactides.     

Metal ion binding modes of hypoxanthine and xanthine versus the versatile behaviour of adenine

The metal coordination patterns of hypoxanthine, xanthine and related oxy-purines have been reviewed on the basis of the structural information available in the Cambridge Structural Database (CSD), including also the most recent reports founded in SciFinder. Attention is paid to the metal ion binding modes and interligand interactions in mixed-ligand metal complexes, as well as the possibilities of metal binding of the exocyclic-O atoms. The information in CSD is also reviewed for the complexes of adenine in cationic, neutral and anionic forms with every metal ion. In contrast to the scarce structural information about hypoxanthine and related complexes, large structural information is available for adenine complexes with a variety of metals that reveals some correlations between the crystal–chemical properties of metal ions. Three aspects are studied in deep: the coordination patterns, the interligand interactions influencing the molecular recognition in mixed-ligand metal complexes and the connectivity between metals for different adenine species, thus supporting its unique versatility as ligand. When possible, the overall behaviour showed by adenine metal complexes is discussed according to the HSAB Pearson criteria and the tautomeric behaviour observed for each protonated species of adenine. The differences between the roles of adenine and the referred oxypurines ligands are underlined.     

Non-conventional coordination of cavity-confined metal centres

WIDEPHOS, a β-cyclodextrin cavitand bearing two introverted P(III) donor atoms, readily accommodates two converging Au-X fragments (X = Cl, Br, I). In the corresponding [(WIDEPHOS)(AuX)(2)] complexes, severe steric crowding within the cavity results in one of the P-Au-X rods deviating from linearity, as revealed by an X-ray diffraction study and unusual (31)P magnetic shielding of one of the two phosphorus signals. The cavitand ligand is also suited for hosting strained dipalladium moieties with a single chlorido bridge, thereby forming dynamic complexes in which ligand coordination to one of the metal centres occurs via an oschelating P,O-subunit.     

Different coordination modes of 2-(diphenylphosphino)azobenzenes in complexation with hard and soft metals

Control of coordination modes of a ligand in metal complexes is significant because the coordination modes influence catalytic properties of transition metal catalysts. Reactions of 2-diphenylphosphinoazobenzenes, which are in equilibrium with the inner phosphonium salts, with ZnCl(2), W(CO)(5)(THF), and PtCl(2)(cod) gave three different coordination types of metal complexes with distinctive UV-vis absorptions. All the complexes were characterized by X-ray crystallographic analyses. In the zinc and tungsten complexes, the source molecule functions as an amide ligand and a phosphine ligand, respectively. In the platinum complex, the phosphorus molecule works as a tridentate ligand with formation of a carbon-platinum bond.     

Low-temperature complexes of europium atoms and dimers with cyanophenylpyridines and alkylcyanophenylpyridines

It is shown by IR-Fourier and UV-visible spectroscopy that two biligand complexes of different stoichiometric composition Ln·2L and 2Ln·2L (Ln = Eu; L = 4-pentyl-4′-cyanophenylpyridine) are formed in the course of low-temperature co-condensation of metal and ligand vapors on the surfaces cooled with liquid nitrogen. Quantum-chemical modeling of the equilibrium structures of the mono-and binuclear complexes of europium with unsubstituted cyanophenylpyridyl and para-ethylcyanophenylpyridyl ligands was carried out. The main geometrical parameters of these compounds were determined. For mononuclear complexes, there is a competition between two mechanisms of coordination of the metal atom: formation of sandwich π complexes by interactions with the π orbitals of the aromatic ligand system and σ coordination at the nitrogen atoms of the pyridine ring. The sandwich structures of the binuclear complexes with 4-ethylcyanophenylpyridine are stabilized by N…H intermolecular contacts between the N atom of the cyano group and the terminal H atom of the ethyl group. The spectral shifts and the relative thermal stability of complexes with varying nuclearity are discussed.     

Design, synthesis and characterization of self-assembled As2L3 and Sb2L3 cryptands

The syntheses and X-ray crystal structures of six new self-assembled supramolecular As and Sb-containing cryptands are described. Analysis in the context of previously reported As(2)L(3) and Sb(2)L(3) cryptands reveals that small differences in ligand geometries result in significant differences in the helicity of the complexes and the stereochemistry of the metal coordination within the assembled complexes. Additionally, a new synthetic route is described which involves exposure of reactants to vacuum to help facilitate self-assembly.     

3,5-二碘水杨醛缩水杨酰肼Schiff碱及其金属配合物的合成与抑菌活性

以吡啶、DMF为溶剂合成了3,5-二碘水杨醛缩水杨酰肼Schiff 碱的过渡金属配合物,用紫外可见光谱、红外光谱、TG-DTA、元素分析及摩尔电导率对配合物进行了表征,推测了配合物的可能结构,并对结构特征进行了分析。 应用紫外光谱和荧光光谱测定方法研究了配合物与ct-DNA的作用,发现这些配合物均以插入方式与ct-DNA作用。 另外,对各配合物作了活性测试,发现它们对阴离子超氧自由基O-·2和藤黄微球菌有良好的抑制作用。     

Synthesis and ESR study of Co and Ni hydrazides and hydroxamates containing 2,6-di-tert-butylphenol moiety in the ligands

A series of Co and Ni hydrazides and hydroxamates containing the 2,6-di-tert-butylphenol moiety as a potential free radical precursor in the ligand environment of the complexes were synthesized. ESR spectroscopy was used to study the dependence of the stability of metal complexes incorporating a paramagnetic center in the ligand on the type of the coordination environment of the metal and the nature of the ligand. The complexes, in which a saturated aliphatic bridging group separates the 2,6-di-tert-butylphenol moiety and the coordination environment of the metal, can undergo oxidation to produce stable paramagnetic species with an unpaired electron in the ligand environment. The interaction of the free radical center in the ligand with the coordination environment of the metal is practically absent (excepting the weak spin-spin interaction). Metal complexes incorporating a hydrazine moiety conjugated with the 2,6-di-tert-butylphenol substituent do not produce detectable stable paramagnetic forms with a free radical in the ligand.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1794–1797, September, 1995.     

联三吡啶配体及其衍生物合成进展

金属-配体间的配位作用是超分子化学中最重要的相互作用之一, 寡聚吡啶配体可以与许多过渡金属离子配位, 形成具有独特磁、光物理和电化学性质的过渡金属络合物, 因此联三吡啶配体的合成及其过渡金属络合物性能研究引起化学家的广泛关注. 综述了联三吡啶配体及其衍生物的合成方法, 主要包括成环缩合反应、过渡金属催化的偶联反应以及其它方法, 并选取具有代表性的实例对联三吡啶配体的结构和合成方法进行详细地阐述.     

Ligand influence on connectivity and processing: magnetic crystals based on metalloceniums and films of TCNE-based magnets (TCNE=tetracyanoethylene)

Molecular materials built from coordination complexes exhibit properties that can be explained through intermolecular electronic interactions driven by the ligand moieties. The nature of the ligand in the precursor molecules governs the connectivity of the magnetic phases and the possibility of producing them by using a gas-phase process. Metallocenium, metal bisdithiolate materials, and solvated and solvent-free [M(tcne)2] (tcne=tetracyanoethylene) magnets illustrate such features.     

Metallogels from Coordination Complexes,Organometallic, and Coordination Polymers

A supramolecular gel results from the immobilization of solvent molecules on a 3D network of gelator molecules stabilized by various supramolecular interactions that include hydrogen bonding, π–π stacking, van der Waals interactions, and halogen bonding. In a metallogel, a metal is a part of the gel network as a coordinated metal ion (in a discrete coordination complex), as a cross‐linking metal node with a multitopic ligand (in coordination polymer), and as metal nanoparticles adhered to the gel network. Although the field is relatively new, research into metallogels has experienced a considerable upsurge owing to its fundamental importance in supramolecular chemistry and various potential applications. This focus review aims to provide an insight into the development of designing metallogelators. Because of the limited scope, discussions are confined to examples pertaining to metallogelators derived from discrete coordination complexes, organometallic gelators, and coordination polymers. This review is expected to enlighten readers on the current development of designing metallogelators of the abovementioned class of molecules.     

Synthesis and structural investigation of tungsten imido amidinate and guanidinate complexes

The tungsten imido guanidinate and amidinate complexes W(NR)Cl(3)[R'NC(NMe(2))NR'] and W(NR)Cl(3)[R'NC(Me)NR'] (R = Ph, (i)Pr, Cy; R' = (i)Pr, (t)Bu, TMS) were synthesized by reacting the corresponding imido complex W(NR)Cl(4)(OEt(2)) with the appropriate lithium amidinate or guanidinate. Crystallographic structure determination of W(N(i)Pr)Cl(3)[(i)PrNC(NMe(2))N(i)Pr] and W(N(i)()Pr)Cl(3)[(i)PrNC(Me)N(i)Pr] allows comparison of structural features between the guanidinate and amidinate ligand in the presence of an identical ancillary ligand set.     

Bending Nanofibers into Nanospirals: Coordination Chemistry as a Tool for Shaping Hydrophobic Assemblies

In the current work, we demonstrate how coordination chemistry can be employed to direct self‐assembly based on strong hydrophobic interactions. To investigate the influence of coordination sphere geometry on aqueous self‐assembly, we synthesized complexes of the amphiphilic perylene diimide terpyridine ligand with the first‐row transition‐metal centers (zinc, cobalt, and nickel). In aqueous medium, aggregation of these complexes is induced by hydrophobic interactions between the ligands. However, the final shapes of the resulting assemblies depend on the preferred geometry of the coordination spheres typical for the particular metal center. The self‐assembly process was characterized by UV/Vis spectroscopy, zeta potential measurements, and cryogenic transmission electron microscopy (cryo‐TEM). Coordination of zinc(II) and cobalt(II) leads to the formation of unique nanospiral assemblies, whereas complexation of nickel(II) leads to the formation of straight nanofibers. Notably, coordination bonds are utilized not as connectors between elementary building blocks, but as directing interactions, enabling control over supramolecular geometry.     

A Study on The Interactions Between Coordination Compounds and Supports

In this study the viewpoint is taken that the supported complexes react with active groups on the surface of the support to form new entities which may be called surface complexes.Various interactions between the support and the solute in solution of impregnation have been found,and these interactions may be divided into four calsses: (1) there is no noticeable chemical interaction between the dissolved coordination compound and the support,except the physical adsorption;(2) the metal ion of the complex is anchored on the surface through the surface group as a ligand forming a surface complex,or the support provides the central ion for the formation of a surface polynuciear complex through the bridging ligand of the complex;(3) the surface of the support provides the central ion for ligands dissociated from the complex or for the solvent molecules;(4) the metal hydroxide might be formed,when the acidity of the cation of the support is weaker than that of the metal ion of the complex in a aqueous solutio     

The protective effect of salicylic acid on lysozyme against riboflavin-mediated photooxidation

Tridentate Schiff base (H(2)L) ligand was synthesized via condensation of o-hydroxybenzaldehyde and 2-aminothiophenol. The metal complexes were prepared from reaction of the ligand with corresponding metal salts presence of substituted pyridine in two different solvents (MeOH or MeCN). The ligand and metal complexes were then characterized by using FTIR, TGA, (1)H NMR and (13)C NMR spectroscopies. The FTIR spectra showed that H(2)L was coordinated to the metal ions in tridentate manner with ONS donor sites of the azomethine N, deprotonated phenolic-OH and phenolic-SH. Furthermore, substituted pyridine was coordinated to the central metal atoms. The thermal behavior of the complexes was investigated by using TGA method and dissociations indicated that substituted pyridine and ligand were leaved from coordination. This coordination of the metal complexes was correlated by (1)H NMR and (13)C NMR. Finally, electrochemical behavior of the ligand and a Ni(II) complex were investigated.