Reactions of Monodithiolene Tungsten(VI) Sulfido Complexes with Copper(I) in Relation to the Structure of the Active Site of Carbon Monoxide Dehydrogenase

Molybdenum-Copper Antagonism In Metalloenzymes And Anti-Copper Therapy

The connection between 3d (Cu) and 4d (Mo) via the "Mo-S-Cu" unit is called Mo-Cu antagonism. Biology offers case studies of such interactions in metalloproteins such as Mo/Cu-CO Dehydrogenases (Mo/Cu-CODH), and Mo/Cu Orange Protein (Mo/Cu-ORP). The CODH significantly maintains the CO level in the atmosphere below the toxic level by converting it to non-toxic CO2 for respiring organisms. Several models were synthesized to understand the structure-function relationship of these native enzymes. However, this interaction was first observed in ruminants, and they convert molybdate (MoO4 2- ) into tetrathiomolybdate (MoS4 2- ; TTM), reacting with cellular Cu to yield biological unavailable Mo/S/Cu cluster, then developing Cu-deficiency diseases. These findings inspire the use of TTM as a Cu-sequester drug, especially for treating Cu-dependent human diseases such as Wilson diseases (WD) and cancer. It is well known that a balanced Cu homeostasis is essential for a wide range of biological processes, but negative consequence leads to cell toxicity. Therefore, this review aims to connect the Mo-Cu antagonism in metalloproteins and anti-copper therapy.

Combining [MoVIO3] and [M0(CO)3] (M = Mo, Cr) Fragments within the Same Complex: Synthesis and Reactivity of the Single Oxo-Bridged Heterobimetallics Supported by Xanthene-Based Heterodinucleating Ligands

A functional model of Mo-Cu carbon monoxide dehydrogenase (CODH) enzyme requires the presence of an oxidant (metal-oxo) and a metal-bound carbonyl in close proximity. In this work, we report the synthesis, characterization, and reactivity of a heterobimetallic complex combining Mo(VI) trioxo with Mo(0) tricarbonyl. The formation of the heterobimetallic complex is facilitated by the xanthene-bridged heterodinucleating ligand containing a hard catecholate chelate and a soft iminopyridine chelate. A catechol-coordinated square-pyramidal [MoVIO3] fragment interacts directly with the iminopyridine-bound [Mo0(CO)3] fragment via a single (oxo) bridge, with the overall disposition being related to the proposed first step in the CODH mechanism, where square-pyramidal [MoVIO2S] interacts with the [Cu-CO] via a single sulfido bridge. Our attempt to obtain a sulfido-bridged analogue (using [MoO3S]2- precursor) led to a mixture of products possibly containing different (oxo and sulfido) bridges. Despite a direct interaction between Mo(VI) and Mo(0) segments, no internal redox is observed, with the high lying occupied MOs being mostly d-π orbitals at Mo0(CO)3 and the low lying unoccupied MOs being d-π orbitals at MoVIO3. Due to the overall rigid structure, the heterobimetallic complex was found to be stable up to 100 °C in DMF-d7 (based on 1H NMR). The decomposition of the complex above this temperature does not produce CO2 (based on gas chromatography), dissociating stable Mo(CO)3(DMF)3 instead (based on IR). We also synthesized and studied the reactivity of the Mo(VI)/Cr(0) analogue. While this complex demonstrated more facile decomposition, no CO2 production was observed. Density functional theory calculations suggest that the formation of [CO2]2- and its subsequent reductive elimination is endergonic in the present system, likely due to the stability of fac-Mo0(CO)3 and the relative nucleophilic character of the carbonyl carbon engendered by back donation from Mo(0). The calculations also indicate that the replacement of one oxo by sulfido (both terminal and bridging), replacement of catechol with dithiolene, and replacement of Mo(0) with Cr(0) does not affect significantly the energetics of the process, likely requiring the use a less stable and less π-basic CO anchor.

Studies Relevant to the Functional Model of Mo-Cu CODH: In Situ Reactions of Cu(I)-L Complexes with Mo(VI) and Synthesis of Stable Structurally Characterized Heterotetranuclear MoVI2CuI2 Complex

In this study, we report the synthesis, characterization, and reactions of Cu(I) complexes of the general form Cu(L)(LigH₂) (LigH₂ = xanthene-based heterodinucleating ligand (E)-3-(((5-(bis(pyridin-2-ylmethyl)amino)-2,7-di-tert-butyl-9,9-dimethyl-9H-xanthen-4-yl)imino)methyl)benzene-1,2-diol); L = PMe₃, PPh₃, CN(2,6-Me₂C₆H₃)). New complexes [Cu(PMe₃)(LigH₂)] and [CuCN(2,6-Me₂C₆H₃)(LigH₂)] were synthesized by treating [Cu(LigH₂)](PF₆) with trimethylphosphine and 2,6-dimethylphenyl isocyanide, respectively. These complexes were characterized by multinuclear NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry (HRMS), and X-ray crystallography. In contrast, attempted reactions of [Cu(LigH₂)](PF₆) with cyanide or styrene failed to produce isolable crystalline products. Next, the reactivity of these and previously synthesized Cu(I) phosphine and isocyanide complexes with molybdate was interrogated. IR (for isocyanide) and ³¹P NMR (for PPh₃/PMe₃) spectroscopy demonstrates the lack of oxidation reactivity. We also describe herein the first example of a structurally characterized multinuclear complex combining both Mo(VI) and Cu(I) metal ions within the same system. The heterobimetallic tetranuclear complex [Cu₂Mo₂O₄(μ₂-O)(Lig)₂]·HOSiPh₃ was obtained by the reaction of the silylated Mo(VI) precursor (Et₄N)(MoO₃(OSiPh₃)) with LigH₂, followed by the addition of [Cu(NCMe)₄](PF₆). This complex was characterized by NMR spectroscopy, high-resolution mass spectrometry, and X-ray crystallography.

Inspired by Nature-Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases

Throughout the previous ten years many scientists took inspiration from natural molybdenum and tungsten-dependent oxidoreductases to build functional active site analogues. These studies not only led to an ever more detailed mechanistic understanding of the biological template, but also paved the way to atypical selectivity and activity, such as catalytic hydrogen evolution. This review is aimed at representing the last decade’s progress in the research of and with molybdenum and tungsten functional model compounds. The portrayed systems, organized according to their ability to facilitate typical and artificial enzyme reactions, comprise complexes with non-innocent dithiolene ligands, resembling molybdopterin, as well as entirely non-natural nitrogen, oxygen, and/or sulfur bearing chelating donor ligands. All model compounds receive individual attention, highlighting the specific novelty that each provides for our understanding of the enzymatic mechanisms, such as oxygen atom transfer and proton-coupled electron transfer, or that each presents for exploiting new and useful catalytic capability. Overall, a shift in the application of these model compounds towards uncommon reactions is noted, the latter are comprehensively discussed.

Oxygen Activation by a Copper Complex with Sulfur-Only Coordination Relevant to the Formylglycine Generating Enzyme

Synthesizing hydrosulfido Cu thiolate complexes is quite challenging. In this report, two new and rare hydrosulfido Cu thiolate complexes, [Et₄N]₂[(mnt)Cu-SH] (2, mnt = maleonitrile dithiolene = S₂C₂(CN)₂) and [Et₄N]₃[(mnt)Cu-(μ-SH)-Cu(mnt)] (3), have been synthesized. Coordination sites and O₂ activation by complex 2 resemble the formylglycine generating enzyme (FGE), an enzyme recently crystallographically characterized with sulfur-only coordination around Cu (three thiolate ligands). The function of this enzyme (and complex 2) is surprising because vulnerable thiolates should not be well suited for O₂ activation rationally. Indeed, activation of oxygen by such an all-sulfur-coordinated Cu complex 2 is lacking in the literature. Aerial O₂ (ambient O₂ from the air) activation by complex 2 could proceed through a superoxide radical intermediate and a sulfur radical intermediate detected by resonance Raman (rR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, respectively. The chemistry of 2 has been examined by its reactivity, crystal structure, and spectroscopic and cyclic voltammetric analyses. In addition, the results have been complemented with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.

Carbon Dioxide Reduction: A Bioinspired Catalysis Approach

While developed in a number of directions, bioinspired catalysis has been explored only very recently for CO₂ reduction, a challenging reaction of prime importance in the context of the energetic transition to be built up. This approach is particularly relevant because nature teaches us that CO₂ reduction is possible, with low overpotentials, high rates, and large selectivity, and gives us unique clues to design and discover new interesting molecular catalysts. Indeed, on the basis of our relatively advanced understanding of the structures and mechanisms of the active sites of fascinating metalloenzymes such as formate dehydrogenases (FDHs) and CO dehydrogenases (CODHs), it is possible to design original, active, selective, and stable molecular catalysts using the bioinspired approach. These metalloenzymes use fascinating metal centers: in FDHs, a Mo(W) mononuclear ion is coordinated by four sulfur atoms provided by a specific organic ligand, molybdopterin (MPT), containing a pyranopterin heterocycle (composed of a pyran ring fused with a pterin unit) and two sulfhydryl groups for metal chelation; in CODHs, catalytic activity depends on either a unique nickel-iron-sulfur cluster or a dinuclear Mo-Cu complex in which the Mo ion is chelated by an MPT ligand. As a consequence, the novel class of catalysts, designed by bioinspiration, consists of mononuclear Mo, W, and Ni and as well as dinuclear Mo-Cu and Ni-Fe complexes in which the metal ions are coordinated by sulfur ligands, more specifically, dithiolene chelates mimicking the natural MPT cofactor. In general, their activity is evaluated in electrochemical systems (cyclic voltammetry and bulk electrolysis) or in photochemical systems (in the presence of a photosensitizer and a sacrificial electron donor) in solution. This research is multidisciplinary because it implies detailed biochemical, functional, and structural characterization of the inspiring enzymes together with synthetic organic and organometallic chemistry and molecular catalysis studies. The most important achievements in this direction, starting from the first report of a catalytically active biomimetic bis-dithiolene-Mo complex in 2015, are discussed in this Account, highlighting the challenging issues associated with synthesis of such sophisticated ligands and molecular catalysts as well as the complexity of reaction mechanisms. While the very first active biomimetic catalysts require further improvement, in terms of performance, they set the stage in which molecular chemistry and enzymology can synergistically cooperate for a better understanding of why nature has selected these sites and for developing highly active catalysts.

Synthesis and Cu(I)/Mo(VI) Reactivity of a Bifunctional Heterodinucleating Ligand on a Xanthene Platform

In an effort to probe the feasibility of a model of Mo-Cu CODH (CODH = carbon monoxide dehydrogenase) lacking a bridging sulfido group, the new heterodinucleating ligand LH₂ was designed and its Cu(I)/Mo(VI) reactivity was investigated. LH₂ ((E)-3-(((5-(bis(pyridin-2-ylmethyl)amino)-2,7-di-tert-butyl-9,9-dimethyl-9H-xanthen-4-yl)imino)methyl)benzene-1,2-diol) features two different chelating positions bridged by a xanthene linker: bis(pyridyl)amine for Cu(I) and catecholate for Mo(VI). LH₂ was synthesized via the initial protection of one of the amine positions, followed by two consecutive alkylations of the second position, deprotection, and condensation to attach the catechol functionality. LH₂ was found to exhibit dynamic cooperativity between two reactive sites mediated by H-bonding of the catechol protons. In the free ligand, catechol protons exhibit H-bonding with imine (intramolecular) and with pyridine (intermolecular in the solid state). The reaction of LH₂ with [Cu(NCMe)₄]⁺ led to the tetradentate coordination of Cu(I) via all nitrogen donors of the ligand, including the imine. Cu(I) complexes were characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), X-ray crystallography, and DFT calculations. Cu(I) coordination to the imine disrupted H-bonding and caused rotation away from the catechol arm. The reaction of the Cu(I) complex [Cu(LH₂)]⁺ with a variety of monodentate ligands X (PPh₃, Cl^-, SCN^-, CN^-) released the metal from coordination to the imine, thereby restoring imine H-bonding with the catechol proton. The second catechol proton engages in H-bonding with Cu-X (X = Cl, CN, SCN), which can be intermolecular (XRD) or intramolecular (DFT). The reaction of LH₂ with molybdate [MoO₄]^2- led to incorporation of [Mo^VIO₃] at the catecholate position, producing [MoO₃(L)]^2-. Similarly, the reaction of [Cu(LH₂)]⁺ with [MoO₄]^2- formed the heterodinuclear complex [CuMoO₃(L)]^-. Both complexes were characterized by multinuclear NMR, UV-vis, and HRMS. HRMS in both cases confirmed the constitution of the complexes, containing molecular ions with the expected isotopic distribution.

Group 11 m-Terphenyl Complexes Featuring Metallophilic Interactions

A series of group 11 m-terphenyl complexes have been synthesized via a metathesis reaction from the iron(II) complexes (2,6-Mes₂C₆H₃)₂Fe and (2,6-Xyl₂C₆H₃)₂Fe (Mes = 2,4,6-Me₃C₆H₂; Xyl = 2,6-Me₂C₆H₃). [2,6-Mes₂C₆H₃M]₂ (1, M = Cu; 2, M = Ag; 6, M = Au) and [2,6-Xyl₂C₆H₃M]₂ (3, M = Cu; 4, M = Ag) are dimeric in the solid state, although different geometries are observed depending on the ligand. These complexes feature short metal-metal distances in the expected range for metallophilic interactions. While 1-4 are readily isolated using this metathetical route, the gold complex 6 is unstable in solution at ambient temperatures and has only been obtained in low yield from the decomposition of (2,6-Mes₂C₆H₃)Au·SMe₂ (5). NMR spectroscopic measurements, including diffusion-ordered spectroscopy, suggest that 1-4 remain dimeric in a benzene-d₆ solution. The metal-metal interactions have been examined computationally using the Quantum Theory of Atoms in Molecules and by an energy decomposition analysis employing natural orbitals for chemical valence.

A Series of Homoleptic Linear Trimethylsilylchalcogenido Cuprates, Argentates and Aurates Cat[Me3SiE-M-ESiMe3] (M = Cu, Ag, Au; E = S, Se)

The syntheses and XRD molecular structures of a complete series of silylsulfido metalates Cat[M(SSiMe₃)₂] (M = Cu, Ag, Au) and corresponding silylselenido metalates Cat[M(SeSiMe₃)₂] (M = Cu, Ag, Au) comprising lattice stabilizing organic cations (Cat = Ph₄P⁺ or PPN⁺) are reported. Much to our surprise these homoleptic cuprates, argentates, and aurates are stable enough to be isolated even in the absence of any strongly binding phosphines or N-heterocyclic carbenes as coligands. Their metal atoms are coordinated by two silylchalcogenido ligands in a linear fashion. The silyl moieties of all anions show an unexpected gauche conformation of the silyl substituents with respect to the central axis Si-[E-M-E]-Si in the solid state. The energetic preference for the gauche conformation is confirmed by quantum chemical calculations and amounts to about 2-6 kJ/mol, thus revealing a rather shallow potential mainly depending on electronic effects of the metal. Furthermore, 2D HMQC methods were applied to detect the otherwise nonobservable NMR shifts of the ²⁹Si and ⁷⁷Se nuclei of the silylselenido compounds. Preliminary investigations reveal that these thermally and protolytically labile chalcogenido metalates are valuable precursors for the precipitation of binary coinage metal chalcogenide nanoparticles from organic solution and for coinage metal cluster syntheses.

A W/Cu Synthetic Model for the Mo/Cu Cofactor of Aerobic CODH Indicates That Biochemical CO Oxidation Requires a Frustrated Lewis Acid/Base Pair

Constructing synthetic models of the Mo/Cu active site of aerobic carbon monoxide dehydrogenase (CODH) has been a long-standing synthetic challenge thought to be crucial for understanding how atmospheric concentrations of CO and CO₂ are regulated in the global carbon cycle by chemolithoautotrophic bacteria and archaea. Here we report a W/Cu complex that is among the closest synthetic mimics constructed to date, enabled by a silyl protection/deprotection strategy that provided access to a kinetically stabilized complex with mixed O^2-/S^2- ligation between (bdt)(O)W^VI and Cu^I(NHC) (bdt = benzene dithiolate, NHC = N-heterocyclic carbene) sites. Differences between the inorganic core's structural and electronic features outside the protein environment relative to the native CODH cofactor point to a biochemical CO oxidation mechanism that requires a strained active site geometry, with Lewis acid/base frustration enforced by the protein secondary structure. This new mechanistic insight has the potential to inform synthetic design strategies for multimetallic energy storage catalysts.

A bioinspired molybdenum-copper molecular catalyst for CO2 electroreduction

A bimetallic Mo–Cu complex inspired by the active site of the carbon monoxide dehydrogenase enzyme mediates the electroreduction of carbon dioxide to formic acid.

Non-noble metal molecular catalysts mediating the electrocatalytic reduction of carbon dioxide are still scarce. This work reports the electrochemical reduction of CO₂ to formate catalyzed by the bimetallic complex [(bdt)Mo^VI(O)S₂Cu^ICN]^2– (bdt = benzenedithiolate), a mimic of the active site of the Mo–Cu carbon monoxide dehydrogenase enzyme (CODH2). Infrared spectroelectrochemical (IR-SEC) studies coupled with density functional theory (DFT) computations revealed that the complex is only a pre-catalyst, the active catalyst being generated upon reduction in the presence of CO₂. We found that the two-electron reduction of [(bdt)Mo^VI(O)S₂Cu^ICN]^2– triggers the transfer of the oxo moiety to CO₂ forming CO₃^2– and the complex [(bdt)Mo^IVS₂Cu^ICN]^2– and that a further one-electron reduction is needed to generate the active catalyst. Its protonation yields a reactive Mo^VH hydride intermediate which reacts with CO₂ to produce formate. These findings are particularly relevant to the design of catalysts from metal oxo precursors.

Models for aerobic carbon monoxide dehydrogenase: synthesis, characterization and reactivity of paramagnetic MoVO(μ-S)CuI complexes

Complexes exhibiting the Mo^VO(μ-S)Cu^I cores, EPR properties, electronic structures and biomimetic reactions of aerobic Mo/Cu-containing carbon monoxide dehydrogenases are reported.

Reaction of [CoCp₂][Tp^iPrMoOS(OAr)] [Cp = η⁵-cyclopentadienyl; Tp^iPr = hydrotris(3-isopropylpyrazol-1-yl)borate; OAr = phenolate or derivative thereof] with [Cu(NCMe)(Me₃tcn)]BF₄ (Me₃tcn = 1,4,7-trimethyl-1,4,7-triazacyclononane) in MeCN at –30 °C results in the formation of red-brown/black, paramagnetic, μ-sulfido-Mo(v)/Cu(i) complexes, Tp^iPrMoO(OAr)(μ-S)Cu(Me₃tcn). The complexes possess the MoO(μ-S)Cu core found in aerobic carbon monoxide dehydrogenases (CODHs) and exhibit X-band EPR spectra closely related to those of semi-reduced CODH, with g_iso ∼ 1.937, hyperfine coupling to ^95,97Mo (a_iso = 39–42 × 10^–4 cm^–1) and strong superhyperfine coupling to ^63,65Cu (a_iso = 34–63 × 10^–4 cm^–1). Anisotropic spectra exhibit monoclinic symmetry with g₁ ∼ 1.996, g₂ ∼ 1.944 and g₃ ∼ 1.882, and nearly isotropic A_Cu values (75–90 × 10^–4 cm^–1). The X-ray structures of four derivatives (Ar = Ph, C₆H₄^tBu-2, C₆H₄^sBu-2, C₆H₄Ph-4) are reported and discussed along with that of the Ar = C₆H₃^tBu₂-3,5 derivative (communicated in C. Gourlay, D. J. Nielsen, J. M. White, S. Z. Knottenbelt, M. L. Kirk and C. G. Young, J. Am. Chem. Soc., 2006, 128, 2164). The complexes exhibit distorted octahedral oxo-Mo(v) and distorted tetrahedral Cu(i) centres bridged by a single bent μ-sulfido ligand, with Mo–S and Cu–S distances and Mo–S–Cu angles in the ranges 2.262–2.300 Å, 2.111–2.134 Å and 115.87–134.27°, respectively. The 2 t-butyl derivative adopts a unique phenolate conformation with O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Mo–O–Cα and O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Mo–S–Cu torsion angles of 92.7 and 21.1°, respectively, very different from those of the other structurally characterized derivatives (31–47 and 33–45°, respectively) and exhibits a relatively short Mo···Cu distance [3.752(2) Å vs. 3.806(7)–4.040(2) Å]. As well, the a_Cu value of this complex (34.3 × 10^–4 cm^–1) is much lower than the values observed for other members of the series (55–63 × 10^–4 cm^–1), supporting the hypothesis that the electronic structure of the MoO(μ-S)Cu core unit and the degree of intermetallic communication are strongly dependent on the geometry of the MoO(OR)(μ-S)Cu unit. The complexes participate in an electrochemically reversible Mo(vi)/Mo(v) redox couple and react with cyanide undergoing decupration and desulfurization reactions of the type observed for CODH.

Cooperative bimetallic reactivity of a heterodinuclear molybdenum–copper model of Mo–Cu CODH

Modeling the reactivity of Mo–Cu CODH: Cu(i) brings the substrate close to Mo–oxo and develops electrophilic character in CO carbon.

A cyclic mixed-valence MoVI/MoV polyoxothiomolybdate cluster anion stabilized by a [(μ-I){Ag(PPh3)3}2]+ complex cation. Preparation and structure of [(μ-I){Ag(PPh3)3}2]2 [Mo8O8(μ-OH)2(μ-OEt)6(μ-S)8(μ3-O)4{Mo(DMF)2}] · 2EtOH

Treatment of (NMe4)2[Mo2O2S6] with Ag(PPh3)3I in the presence of NaOEt in DMF/EtOH resulted in the formation of a novel MoVI/MoV polyoxothiomolybdate cluster compound [(μ-I){Ag(PPh3)3}2]2[Mo8O8(μ-OH)2 (μ-OEt)6(μ-S)8(μ3-O)4{Mo(DMF)2}] · 2EtOH. The cyclic cluster polyanion consists of an octamer {Mo8O8(μ-OH)2(μ-OEt)6 (μ-S)8(μ3-O)4} that encapsulates a central {MoVI(DMF)2 (μ3-O)4} octahedron.

Bioinorganic modeling chemistry of carbon monoxide dehydrogenases: description of model complexes, current status and possible future scopes

Carbon monoxide dehydrogenases (CODHs) use CO as their sole source of carbon and energy and are found in both aerobic and anaerobic carboxidotrophic bacteria. Reversible transformation of CO to CO2 is catalyzed by a bimetallic [Mo-(μ2-S)-Cu] system in aerobic and by a highly asymmetric [Ni-Fe-S] cluster in anaerobic CODH active sites. The CODH activity in the microorganisms effects the removal of almost 10(8) tons of CO annually from the lower atmosphere and earth and thus help to maintain a sub-toxic concentration of CO. Despite an appreciable amount of work, the mechanism of CODH activity is not clearly understood yet. Moreover, biomimetic chemistry directed towards the active sites of CODHs faces several synthetic challenges. The synthetic problems associated with the modeling chemistry and strategies adopted to overcome those problems are discussed along with their limitations. A critical analysis of the exciting results delineating the present status of CODH modeling chemistry and its future prospects are presented.

Linear Cu(i) chalcogenones: synthesis and application in borylation of unsymmetrical alkynes

The synthesis, properties and catalytic application of homoleptic copper(i) imidazoline-2-chalcogenone complexes are described.

Synthesis and characterization of mononuclear Zn(II), Co(II) and Ni(II) complexes containing a sterically demanding silanethiolate ligand derived from tris(2,6-diisopropylphenoxy)silanethiol

Four heteroleptic complexes of nickel(ii), cobalt(ii) and zinc(ii), containing a monodentate silanethiolate ligand derived from tris(2,6-diisopropylphenoxy)silanethiol (TDST), were prepared and characterized. Nickel(ii) and cobalt(ii) complexes of the formula M(NH3)2(TDST)2 (M = Ni(ii) complex , M = Co(ii) complex ) were obtained from the respective chlorides. Zinc complexes of the general formula Zn(acac)(TDST)(L), where L = EtOH (complex ) or H2O (complex ), were obtained from zinc acetylacetonate. A single-crystal X-ray structural analysis revealed that all crystalline products are solvent adducts. The geometries of ligands in the complexes are typical: distorted tetrahedral in zinc and cobalt(ii) complexes and square planar in nickel(ii) compounds. Magnetic studies performed for Ni(ii) and Co(ii) compounds confirmed the diamagnetic character of the first complex and high-spin paramagnetic configuration of the latter. Nickel(ii) and cobalt(ii) complexes were additionally characterized by UV-Vis and IR spectroscopy. IR bands for ligands in the complexes were assigned with the help of the DFT vibrational frequency calculations.

Alkali/coinage metals – organolithium, organocuprate chemistry

Part 1 of this chapter reviews coordination compounds of the alkali metals that contain a carbon-metal bond, looking firstly at organolithiums involving simple silanes. The use of aryl, alkynyl and N-donor ligands is also discussed. Compounds of the coinage metals - copper, silver and gold - are discussed in Part 2 of the review. Discussion is broken down by metal, with copper being considered first. Compounds containing, among others, alkene, amido and phosphido ligands are discussed, along with the significant amount of work on carbene complexes. This interest in carbene complexes is also noted within the silver and gold sections that follow, with a large number of new compounds being described. Polymeric chains and networks containing silver centres have attracted considerable interest and are described, along with the luminescent properties of a selection of novel gold species. This part of the review is completed by coverage of mixed-coinage metal structures, where the systems are found to display luminescent properties. Here again, the compounds discussed contain at least one carbon-metal bond.

Remote effects of axial ligand substitution in heterometallic Cr≡Cr···M chains

The heterometallic complexes CrCrM(dpa)(4)Cl(2) (dpa = 2,2'-dipyridylamide) featuring linear Cl-Cr≡Cr···M-Cl chains can regiospecifically be modified via axial ligand substitution to yield OTf-Cr≡Cr···M-Cl chains (OTf = triflate) with M being Fe, Mn, or Co. The effect of OTf substitution on the Cr side of the molecule has an unusual and profound structural impact on the square-pyramidal transition metal M. Specifically, elongation of the four equatorial M-N(py) bonds and the axial M-Cl bonds by 0.03 and 0.09 Å for Fe and 0.07 and 0.11 Å for Mn is observed. The longer M-Cl and M-N(py) bonds result from subtle interactions between the equatorial dpa ligand and the three metal ions. The equatorial dpa ligand responds to the introduction of the more labile OTf ligand at Cr by binding more strongly to this Cr ion which in turn weakens bonding to M. The ligand field experienced by M can be tuned by changing the Cr axial ligand, and this effect is observed in electrochemical measurements of the iron compounds.

Structural distortions upon oxidation in heteroleptic [Cp(2)W(dmit)] tungsten dithiolene complex: combined structural, spectroscopic, and magnetic studies

Four different cation radical salts are obtained upon electrocrystallization of [Cp(2)W(dmit)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in the presence of the BF(4)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions. In these formally d(1) cations, the WS(2)C(2) metallacycle is folded along the S···S hinge to different extents in the four salts, an illustration of the noninnocent character of the dithiolate ligand. Structural characteristics and the charge distribution on atoms, for neutral and ionized complexes with various folding angles, were calculated using DFT methods, together with the normal vibrational modes and theoretical Raman spectra. Raman spectra of neutral complex [Cp(2)W(dmit)] and its salts formed with BF(4)(-), AsF(6)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions were measured using the red excitation (λ = 632.8 nm). A correlation between the folding angle of the metallacycle and the Raman spectroscopic properties is analyzed. The bands attributed to the C═C and C-S stretching modes shift toward higher and lower frequencies by about 0.3-0.4 cm(-1) deg(-1), respectively. The solid state structural and magnetic properties of the three salts are analyzed and compared with those of the corresponding molybdenum complexes. Temperature dependence of the magnetic susceptibility shows the presence of one-dimensional antiferromagnetic interactions in the BF(4)(-), PF(6)(-), and [Au(CN)(2)](-) salts, while an antiferromagnetic ground state is identified in the Br(-) salt below T(Néel) = 7 K. Interactions are systematically weaker in the tungsten salts than in the isostructural molybdenum analogs, a consequence of the decreased spin density on the dithiolene ligand in the tungsten complexes.