Further synthetic investigation of the general lanthanoid(iii) [Ln(iii)]/copper(ii)/pyridine-2,6-dimethanol/carboxylate reaction system: {CuII5LnIII4} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(iii) analogue

A new family of {Cu5Ln4} complexes bearing the dianionic form of pyridine-2,6-dimethanol (pdm2−) and ancillary ButCH2CO2− carboxylate groups is reported and magnetically studied.

Electrochemical and Computational Insights into the Reduction of [Fe2(CO)6{µ-(SCH2)2GeMe2}] Hydrogenase H-Cluster Mimic

The electrochemical reduction of the complex [Fe2(CO)6{µ-(SCH2)2GeMe2}] (1) under N2 and CO is reported applying cyclic voltammetry. Reduction of complex 1 in CO saturated solutions prevents the possible release of CO from the dianion 12−, while the latter reacts with additional CO forming a spectroscopically uncharacterized product P1. This product undergoes a reversible redox process at E1/2 = −0.70 V (0.2 V∙s−1). In this report, the structure of the neutral complex 1, isomers of dianionic form of 1, and P1 are described applying DFT computations. Furthermore, we propose reaction pathways for H2 production on the basis of the cyclic voltammetry of complex 1 in presence of the strong acid CF3SO3H.

Cyclic Aromaticity within Huckel and Quasi-Correlated Huckel-like Models

The paper deals with quantifying aromaticity in π-electron networks by unsophisticated MO techniques. The focus is placed on local aromaticity measures associated with individual benzenoid rings. We revised the ring aromaticity index due to Cioslowski et al (2007) by including explicitly net charges and electron unpairing effects. Our previously introduced quasi-correlated tight-binding (QCTB) approximation serves here as an easily available tool for taking account of π-electron correlations. The latter crucially influence the behavior of large and even small conjugated π-structures with a nontrivial topology. Numerical applications of Hückel and QCTB models to measuring local aromaticity are reported for various structural classes (polycyclic aromatic hydrocarbons (PAHs), graphene nanoflakes, and others). We analytically investigate the aromaticity in conjugated monocycles CNHN (neutral and charged ones). Furthermore, in the same manner several PAH structures (oligocenes, pyrene, perylene, etc.) are considered in their charged states, and the results are compared with those of related quinoid-type systems, such as p-diphenoquinodimethane. It is shown that, unlike usual PAHs, quinodimethane structures tend to increase their aromaticity in dicationic (dianionic) form. In our studies of nanographene aromaticity we find a decrease of the local aromaticity as we move to a center of graphene structures, that is in a sharp contrast to the predictions of NICS (nucleus independent chemical shift), a rather criticized approach. A particular emphasis is being put on measuring local aromaticity in highly correlated π-systems. Typical non-Kekule hydrocarbons (e.g., triangulene radical and polyradicals), are also studied within QCTB by which characteristic difficulties caused by the occurrence of many non-bonding π-MOs, are simply obviated.

Cu(II), Cd(II) and Ni(II) Complexes of 5-Bromosalicylaldehyde-4-hydroxybenzhydrazone: Synthesis and Spectral Studies

Four complexes of 5-bromosalicylaldehyde-4-hydroxybenzhydrazone were synthesized and characterized by elemental analyses, electronic, and infrared spectra. In all complexes, hydrazone exists either in the neutral form, deprotonated monoanionic form or in dideprononated dianionic form. Structures were assigned to all the complexes based on the physico-chemical studies.

Crystal structure ofcatena-poly[[copper(II)-μ2-salicylato-[diaquacopper(II)]-μ2-salicylato] dihydrate]

The title compound, {[Cu2(C7H4O3)2(H2O)2]·2H2O}n, contains two copper(II) cations in special positions (one on a twofold rotation axis and one on an inversion centre) and the the salicylate ligand in its dianionic form. By four- and six-coordinate metal coordination, chains are formed parallel to [001], which are extended by O—H...O hydrogen bonding into sheets extending parallel to (100). These sheets are weakly connected by O—H...O hydrogen bondingviathe non-coordinating lattice water molecules into a three-dimensional network.

Coordination Polymers Constructed from TCNQ2– Anions and Chelating Ligands

Coordination polymers containing tetracyanoquinodimethane (TCNQ) in its dianionic form, TCNQ–II, have been formed by combining the acid form of the dianion, TCNQH2, with divalent metal centres in the presence of chelating ligands such as 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen). When MnII or CdII is employed, two-dimensional (2D) corrugated sheet structures with the formula MII(TCNQ–II)L (M = Mn, Cd; L = bipy, phen) are obtained. In contrast, when CoII is used as the metal centre a complex three-dimensional (3D) structure of composition [CoII(TCNQ–II)(phen)] is formed. Despite the significant differences between the 2D and 3D network structures, the metal coordination geometry and the binding mode of the TCNQ dianion are very similar in all cases.

The mechanism of catalysis and the inhibition of the Bacillus cereus zinc-dependent β-lactamase

The plot of kcat/Km against pH for the Bacillus cereus569/H β-lactamase class B catalysed hydrolysis of benzylpenicillin and cephalosporin indicates that there are three catalytically important groups, two of pKa 5.6±0.2 and one of pKa 9.5±0.2. Below pH 5 there is an inverse second-order dependence of reactivity upon hydrogen ion concentration, indicative of the requirement of two basic residues for catalysis. These are assigned to zinc(II)-bound water and Asp-90, both with a pKa of 5.6±0.2. A thiol, N-(2´-mercaptoethyl)-2-phenylacetamide, is an inhibitor of the class B enzyme with a Ki of 70 µM. The pH-dependence of Ki shows similar pH inflections to those observed in the catalysed hydrolysis of substrates. The pH-independence of Ki between pH 6 and 9 indicates that the pKa of zinc(II)-bound water must be 5.6 and not the higher pKa of 9.5. The kinetic solvent isotope effect on kcat/Km is 1.3±0.5 and that on kcat is 1.5. There is no effect on reactivity by either added zinc(II) or methanol. The possible mechanisms of action for the class B β-lactamase are discussed, and it is concluded that zinc(II) acts as a Lewis acid to stabilize the dianionic form of the tetrahedral intermediate and to provide a hydroxide-ion bound nucleophile, whereas the carboxylate anion of Asp-90 acts as a general base to form the dianion and also, presumably, as a general acid catalyst facilitating C–N bond fission.