D-block Metal Research Articles

Small-Molecule Fluorescent Sensors for Investigating Zinc Metalloneurochemistry

The metalloneurochemistry of Zn(II) is of substantial current interest. Zinc is the second most abundant d-block metal ion in the human brain, and its distribution varies with relatively high concentrations found in the hippocampus. Brain zinc is generally divided into two types, protein-bound and loosely bound, the latter also being termed histochemically observable, chelatable, labile, or mobile zinc. The neurophysiological and neuropathological significance of mobile Zn(II) remains enigmatic. Studies of Zn(II) distribution, translocation, and function in vivo require tools for its detection. Because Zn(II) has a closed-shell d(10) configuration and no convenient spectroscopic signature, fluorescence is a well-suited method for monitoring Zn(II) in biological contexts. This Account summarizes work by our laboratory addressing the design, preparation, characterization, and use of small-molecule fluorescent sensors for imaging Zn(II) in living cells and samples of brain tissue. These sensors provide "turn-on" or ratiometric Zn(II) detection in aqueous solution at neutral pH. By making alterations to the Zn(II)-binding unit and fluorophore platform, we have devised sensors with varied photophysical and metal-binding properties. Several of these probes have been applied to image Zn(II) distribution, uptake, and mobilization in a variety of cell types, including neuronal cultures.

Synthesis and Characterizations of Dinuclear Dioxomolybdenum(VI) Complexes with Thiocarbohydrazides of Salicylaldehyde, Bridged by 4,4'-Dipyridyl or Its Derivatives

The tauto-merism (Scheme 1) of these ligands as well as the wellknown tendency of sulfur donors to act as bridging ligandsallows various structural possibilities for the correspondingmetal complexes. As part of our studies on the coordination chemistry of d-block metal complexes with schiff base ligands, we haveearlier reported the synthesis and spectroscopic and electro-chemical properties for the dioxomolybdenum(VI) com-plexes, such as [MoO

Tetravalent Metal Complexation by Keggin and Lacunary Phosphomolybdate Anions

We report the synthesis, spectroscopic and structural characterization, and computational analysis of a series of phosphomolybdate complexes with tetravalent metal cations. The reaction between Ce (IV) and Th (IV) with phosphomolybdate at the optimum pH for the stabilization of the lacunary heteropolyoxometalate anion, [PMo 11O 39] (7-), results in the formation of compounds containing the anions [Ce(PMo 11O 39) 2] (10-) and [Th(PMo 11O 39) 2] (10-), respectively. Single crystal X-ray diffraction analysis was performed on salts of both species, Cs 10[Ce(PMo 11O 39) 2].20H 2O and (NH 4) 10[Th(PMo 11O 39) 2].22H 2O. In both anionic complexes the f-block metal cation is coordinated to the four unsaturated terminal lacunary site oxygens of each [PMo 11O 39] (7-) anion, yielding 8 coordinate sandwich complexes, analogous to previously prepared related complexes. Spectroscopic characterization points to the stability of these complexes in solution over a reasonably wide pH range. Density functional analysis suggests that the Ce-O bond strength in [Ce(PMo 11O 39) 2] (10-) is greater than the Th-O bond strength in [Th(PMo 11O 39) 2] (10-), with the dominant bonding interaction being ionic in both cases. In contrast, under similar reaction conditions, the dominant solid state Zr (IV) and Hf (IV) complexes formed contain the anions [Zr(PMo 12O 40)(PMo 11O 39)] (6-) and [Hf(PMo 12O 40)(PMo 11O 39)] (6-), respectively. In these complexes the central Group 4 d-block metal cations are coordinated to the four unsaturated terminal lacunary site oxygens of the [PMo 11O 39] (7-) ligand and to four bridging oxygens of a plenary Keggin anion, [PMo 12O 40] (3-). In addition, (NH 4) 5{Hf[PMo 12O 40][(NH 4)PMo 11O 39]}.23.5H 2O can be crystallized as a minor product. The structure of the anion, {Hf[PMo 12O 40][(NH 4)PMo 11O 39]} (5-), reveals coordination of the central Hf (IV) cation via four bridging oxygens on both the coordinated [PMo 11O 39] (7-) and [PMo 12O 40] (3-) anions. Unusually, the highly charged lacunary site remains uncoordinated to the Hf metal center but instead interacts with an ammonium cation. (31)P NMR indicates that complexation of the Keggin anion, [PMo 12O 40] (3-), to Hf (IV) and Zr (IV) will stabilize the Keggin anion to a much higher pH than usually observed.

Acyclic Bis(N2O2 chelate) Ligand for Trinuclear d-Block Homo- and Heterometal Complexes

We have synthesized a new type of acyclic bis(N2O2 chelate) ligand that affords a C-shaped O6 site by the metalation of the N2O2 salamo sites. UV-vis titration clearly showed that complexation of H4L with MII (MnII, CoII, and NiII) affords the 1:3 complex [LM3]2+ in a cooperative fashion, whereas complexation with copper(II) gave two or more complexes in a stepwise fashion. The manganese(II) complex [LMn3(OAc)2(MeOH)2] crystallizes in the triclinic system, space group P_1, with unit cell parameters a = 9.584(6) A, b = 13.666(9) A, c = 15.566(10) A, alpha = 108.702(8) degrees, beta = 95.255(4) degrees, gamma = 101.023(8) degrees, and Z = 2, and the cobalt(II) complex [LCo3(OAc)2(EtOH)2].2CHCl3 crystallizes in the triclinic system, space group P_1, with unit cell parameters a = 13.291(6) A, b = 13.913(7) A, c = 14.599(8) A, alpha = 88.27(2) degrees, beta = 67.391(15)degrees, gamma = 73.90(2) degrees, and Z = 2. In the crystal structures, three metal ions occupied both the N2O2 and O6 sites of the ligand L4-. The resultant trinuclear complexes have a C- or S-shaped structure depending on the metal employed. The different nature of the N2O2 and O6 sites of the ligand H4L leads to the site-selective introduction of two different d-block transition metals. An X-ray crystallographic analysis revealed the structures of the two heterotrinuclear complexes, [LZn2Mn(OAc)2(MeOH)2] and [LCu2Zn(OAc)2(H2O)].

Imidazo[4,5-f]-1,10-phenanthrolines: Versatile Ligands for the Design of Metallomesogens

2-Aryl-substituted imidazo[4,5-f]-1,10-phenanthrolines were used as building blocks for metal-containing liquid crystals (metallomesogens). Imidazo[4,5-f]-1,10-phenanthrolines are versatile ligands because they can form stable complexes with various d-block transition metals, including platinum(II) and rhenium(I), as well as with lanthanide(III) and uranyl ions and they can easily be structurally modified by a judicious choice of benzaldehyde precursor. None of the ligands designed for this study were liquid-crystalline. However, mesomorphism could be induced by their coordination to various metallic fragments. The thermal behavior of the metal complexes depended on the metal-to-ligand ratio and the substitution pattern of the coordinating ligands. Complexes with a metal-to-ligand ratio of 1:1 [ML, with M = Pt(II), Re(I)] were not liquid-crystalline. The lanthanide(III) complexes with a metal-to-ligand ratio of 1:2 [ML2, with M = Ln(III)] formed an enantiotropic cubic mesophase or were not liquid-crystalline, depending on the nature of the lanthanide(III) ion and the substitution pattern of the ligands. A 1:3 uranyl complex of the type [ML3]2+ exhibited a hexagonal columnar mesophase over a broad temperature range. Self-assembled monolayers of a europium(III) complex were investigated by scanning tunneling microscopy, which revealed that the complex formed well-ordered structures over long distances at the 1-octanoic acid−graphite interface. The rhenium(I) complexes and the europium(III) complexes with 2-thenoyltrifluoroacetonate or dibenzoylmethanate and imidazo[4,5-f]-1,10-phenanthroline showed good luminescence properties.

Strained Metallocenophanes and Related Organometallic Rings Containing π‐Hydrocarbon Ligands and Transition‐Metal Centers

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Three in a Column

CHEMISTRY Numerous compounds comprising two bonded metal centers stabilized by bulky organic ligands have been characterized. However, zinc, cadmium, and mercury, which straddle the boundary between d-block and p-block metals, have only very recently been observed in this motif. Zhu et al.

Strained Metallocenophanes and Related Organometallic Rings Containing π‐Hydrocarbon Ligands and Transition‐Metal Centers

The structures, bonding, and ring-opening reactions of strained cyclic carbon-based molecules form a key component of standard textbooks. In contrast, the study of strained organometallic molecules containing transition metals is a much more recent development. A wealth of recent research has revealed fascinating nuances in terms of structure, bonding, and reactivity. Building on initial work on strained ferrocenophanes, a broad range of strained organometallic rings composed of a variety of different metals, pi-hydrocarbon ligands, and bridging elements has now been developed. Such strained species can potentially undergo ring-opening reactions to functionalize surfaces and ring-opening polymerization to form easily processed metallopolymers with properties determined by the presence of the metal and spacer. This Review summarizes the current state of knowledge on the preparation, structural characterization, electronic structure, and reactivity of strained organometallic rings with pi-hydrocarbon ligands and d-block metals.

Lauric acid as biological active ligand for complexation with d-block metals

Complexes of lauric acid with general formula M(L)2 · xH2O (M = Cu, Co, Ni, Mn) and M(L)2 (M = Zn, Hg) where L = (CH3(CH2)10COOH) have been synthesized. Their elemental analyses show the good agreement between calculated and experimental values. These complexes have been characterized by spectroscopic techniques, such as IR, UV-visible, atomic absorption, and mass spectrometry, which show that the carboxylate group acts as bidentate in the solid state. Kinetic parameters, such as the order of reaction, activation energy, enthalpy, and entropy were calculated using the Coats and Horowitz methods. The calculated values are in a good agreement with the observed TG values that confirm the structural integrity of the complexes. These complexes were screened for their in vitro biological activities against different bacteria and fungi to establish their significance.

A Facile and Efficient Deoxygenation of Sulfoxides with Mo(CO)6

The deoxygenation of sulfoxides to sulfides is a valuable transformation in the application of organosulfur compounds in organic synthesis. Accordingly, a good number of methods have been developed for the reduction of sulfoxides to the corresponding sulfides. 1 However, they often suffer from serious disadvantages, such as functional group incompatibility, difficult work-up procedures, harsh reaction conditions, or not readily available reagents. Further some of these methods are associated with limitations regarding low yields, prolonged reaction times, and intricate procedures. Therefore, there still exists a search for new improved methods based on easily accessible reagents and operationally simple procedures for the reduction of sulfoxides. The use of oxophilic dblock metals have become important in deoxygenation of various types of organic molecules. 2 In this regard, the selective reduction of azides, nitro compounds and hydroxylamines to amines and deoxygenation of epoxides have been accomplished with Mo(CO)6. 3 Recently, we have reported

Al, Ga and In heterometallic wheels and their by-products

Cyclic octanuclear complexes, each containing seven group 13 metals and one d-block metal are reported and preliminary physical characterisation of the compounds discussed.

Effects of p- and d-block metal co-substitution on the electronic structure and physicochemical properties of InMO 4 (M = Nb and Ta) semiconductors

We have investigated the effect of the co-substitution of Sn IV and Ni II ions on the electronic structure and physicochemical property of InMO 4 (M = Nb, Ta) semiconductors. The co-substitution leads to a red-shift of absorption edge as well as to an appearance of satellite peak below the absorption edge. Depending on the nature of valence orbitals, the substitution of p- and d-block elements results in the lowering of conduction band and the formation of impurity states in the middle of bandgap, respectively. Such a band modification makes the photocatalytic activity of InMO 4 improved against the photodegradation of organic molecules.

New type of compounds based on s-and d-block metal trimethylacetates

Heterometallic compounds based on alkali (Li, Na, K, Rb, or Cs) trimethylacetates and transition metal (Cu or Co) trimethylacetates were synthesized. These compounds are characterized by a larger number of s-block atoms compared to d-block atoms. An excess alkali metal trimethylacetate in the reaction system leads to the formation of unusual polymeric systems containing alternating s-and d-block atoms.

Temperature-dependent thermo-elastic properties of s-, p- and d-block liquid metals

Thermodynamic relations involving experimentally known physical quantities are used to determine the ratio of specific heats, γ, for s-block (Na, K, Rb, Cs, Mg), d-block (Fe, Co, Ni, Cu, Ag, Au, Zn, Cd, Hg,) and p-block (Al, Ga, In, Tl, Sn, Pb, Sb, Bi, Se, Te) liquid metals. γ is further utilized to determine reliable values for the isothermal compressibility ( κ T ) and the specific heat at constant volume ( C V ) for these liquid metals near and above the melting temperatures. These data are of considerable significance for various thermo-physical analysis of liquid metals. We have also evaluated the Grüneisen function and its temperature dependence to establish the correlation between the thermal expansion and the elastic response to thermally induced stress. The values of acoustic impedance for liquid metals are evaluated and its physical significance is discussed for the transmission of elastic waves across metallic interfaces.

Adventures with Substances Containing Metals in Negative Oxidation States

A brief history of substances containing s,p- and d-block metals in negative oxidation states is described. A classification of these species and discussions of formal oxidation state assignments for low-valent transition metals in complexes are included, along with comments on the innocent and noninnocent character of ligands in metalates. Syntheses of highly reduced carbonyl complexes formally containing transition metals in their lowest known oxidation states of III- and IV- are discussed. Atmospheric-pressure syntheses of early-transition-metal carbonyls involving alkali-metal polyarene-mediated reductions of non-carbonyl precursors have been developed. In the absence of carbon monoxide, these reactions afford homoleptic polyarenemetalates, including the initial species containing three aromatic hydrocarbons bound to one metal. In several instances, these metalates function as useful synthons for "naked" spin-paired atomic anions of transition metals.

PH-Regulated “Off–On” fluorescence signalling of d-block metal ions in aqueous media and realization of molecular IMP logic function

The potential of an anionic receptor moiety in “Off–On” fluorescence signalling of d-block metal ions has been exploited with the demonstration of a two-input IMP function.

Synthesis, structure, and redox states of homoleptic d-block metal complexes with bis-1,2,4-triazin-3-yl-pyridine and 1,2,4-triazin-3-yl-bipyridine extractants

It has been established that triazinyl bipyridines ( hemi-BTPs) and bis-triazinyl pyridines (BTPs), ligands which are currently being investigated as possible ligands for the separation of actinides from lanthanides in nuclear waste, are able to form homoleptic complexes with first row transition metals such as cobalt(II), copper(II), iron(II), manganese(II), nickel(II) and zinc(II). The metal complexes exhibit six-co-ordinate octahedral structures and redox states largely analogous to those of the related terpyridine complexes. The reactivity of the different redox states of cobalt bis- hemi-BTP complex in aqueous environments has been studied with two-phase electrochemistry by immobilisation of the essentially water-insoluble metal complexes on graphite electrodes and the immersion of this modified electrode in an aqueous electrolyte. It was found that redox potentials for the metal-centred reactions were pH-independent whereas the potentials for the ligand-centred reactions were strongly pH-dependent. The reductive degradation of these complexes has been investigated by computational methods. Solvent extraction experiments have been carried out for a range of metals and these show that cobalt(II) and nickel(II) as well as palladium(II), cadmium(II) and lead(II) were all extracted with the ligands 1e and 2c with higher distribution ratios that was observed for americium(III) under the same conditions. The implications of this result for the use of these ligands to separate actinides from nuclear waste are discussed.

Supramolecular architecture constructed by p-carboxycinnamic acid and d-block metal ions

Four new complexes, [Zn(cca)(phen)] n ( 1), [Co(cca) 0.5(Hcca)(phen)(H 2O)] ( 2), [Cu(cca)(phen)] n · nH 2O ( 3), and [Mn(cca)(phen)(H 2O)] n · 0.25 nH 2O ( 4) (H 2cca = p-carboxycinnamic acid, phen = 1,10-phenanthroline) were synthesized by hydrothermal reactions and characterized by single crystal X-ray diffraction. Complex 1 is of 3D structure constructed by coordination bonds, while complexes 2– 4 consist of 3D supramolecular networks, which are assembled by coordination bonds, hydrogen bonds and π–π stacking interactions. In these complexes, p-carboxycinnamate anions (Hcca − and cca 2−) adopt tetradentate, bidentate and monodentate modes to coordinate to metal ions, resulting in variety of supramolecular structures.

Synthesis and structures of M[N(TePPri2)2-Te,Te′]n(n= 2, M = Zn, Cd, Hg; n= 3, M = Sb, Bi): the first ditelluroimidodiphosphinato p- and d-block metal complexes

Reactions of Na[N(TePPri2)2] with the appropriate metal halide produce the air-stable complexes M[N(TePPri2)2-Te,Te']n (n = 2, M = Zn, Cd, Hg; n = 3, M = Sb, Bi), which adopt distorted tetrahedral (M = Zn, Cd, Hg) and octahedral (M = Sb, Bi) structures, respectively.

Ruthenium as an Effective Nitric Oxide Scavenger

Whilst nitric oxide (NO) has emerged as one of the most versatile and ubiquitous molecules in the human body with a diverse range of physiological functions, dysfunction in NO biosynthesis or metabolism has led to the pathogenesis of a number of disease states. A variety of therapeutic strategies have therefore emerged that either reduce or increase endogenous NO levels depending on the disease pathology. The predominant strategy to date to reduce levels of NO is to utilise specific isoform selective inhibitors of nitric oxide synthases, the enzymes responsible for NO biosynthesis. An alternative line of attack, not related to specificity for a particular enzyme, but rather on compartmental localisation and pharmacokinetics, is to remove or scavenge the excess NO responsible for the disease pathology. In this regard, a number of NO scavenger molecules have demonstrated pharmacological activity across a broad spectrum of disease states. This review will highlight the rationale behind the development, and the current state of play, of one such class of NO scavengers, complexes of the d-block transition metal ruthenium. Prior to this, a brief overview of the remarkable diversity of NO, both from a chemical and biological viewpoint, will be provided for perspective.