Electron-Triggered Imine Coupling: Synthesis and Characterization of Three Redox States (0,-1,-2) of a Ni(N2 S2 ) Complex.

Metal imine-thiolate complexes, M(NS)2 are known to undergo imine C-C bond formation to give M(N2 S2 ) complexes (M=Co, Ni) containing a redox-active ligand. Although these transfor-mations are not typically quantitative, we demonstrate here that the one-electron reduction of a related Ni bis(imine-thiolate) complex affords the corresponding paramagnetic [Ni(N2 S2 )]- anion (2⋅- ) exclusively; subsequent oxidation with [Cp2 Fe]BF4 then affords a high yield of neutral 2 (Cp=η5 -cyclopentadienyl). Moreover, electrochemical studies indicate that a second one-electron reduction affords the diamagnetic dianion. Both anionic products were isolated and characterized by SC-XRD and their electronic structures were investigated by UV-vis spectro-electrochemistry, EPR and NMR spectroscopy, and DFT studies. These studies show that reduction proceeds primarily on the ligand, with (N2 S2 )4- containing both thiolate and ring-delocalized anions.

A Bimetallic Benzene-1,2,4,5-Tetrathiolate (btt) Molybdenocene Complex Cp2 Mo(btt)MoCp2 : Radical and Diradical States.

Benzene-1,2,4,5-tetrathiolate (btt) has been used as a bridging ligand to prepare a redox active (molybdenocene dithiolene)-based bimetallic complex Cp2 Mo(btt)MoCp2 , which exhibits four successive electron transfers up to the tetracation. Spectro-electrochemical investigations together with DFT and TD-DFT calculations evidence that the two electroactive MoS2 C2 metallacycles are electronically coupled in the monocationic as in the dicationic state. Two salts of the dication [Cp2 Mo(btt)MoCp2 ]2+ have been structurally characterized with PF6 - and HSO4 - counterions, showing different chair or boat conformations associated with variable folding angles of the two MoS2 C2 metallacycles along the S-S hinge. The bis-oxidized dicationic complex exhibits a diradical character, with both radicals essentially localized on the metallacycles and with antiferromagnetic coupling evidenced from magnetic susceptibility measurements.

Syntheses and structural characterization of divalent metal complexes (Co, Ni, Pd and Zn) of sterically hindered thiourea ligand and a theoretical insight of their interaction with SARS-CoV-2 enzyme.

Reacting two equivalents of sterically hindered 1,3-bis(2,6-diethylphenyl)thiourea ligand (L) with CoCl2, NiBr2, PdX2 (X = Cl; Br) and ZnI2 in acetonitrile afforded the corresponding bulky thiourea ligand stabilized four coordinated monomeric [L2CoCl2] (1), [L2NiBr2] (2), [L2PdX2] (3a: X = Cl; 3b: X = Br) and [L2ZnI2] (4.2CH3CN) complexes. Compound 1, 2 and 4.2CH3CN are tetrahedral whereas Pd complexes (3a and 3b) are square planar. In solution, palladium complexes are dominated by cis-isomers. Structural characterization shows inter- and intramolecular hydrogen bonding. Hirshfeld surface and fingerprint plots indicated significant intermolecular interactions in the crystal network. Molecular docking analysis revealed relatively higher SARS-CoV-2 enzyme interacting abilities of the synthesized complexes compared to the free ligand. All compounds have been characterized by elemental analyses, NMR spectroscopy and single-crystal X-ray diffraction.

Mononuclear Tricoordinate Copper(I) and Silver(I) Halide Complexes of a Sterically Bulky Thiourea Ligand and a Computational Insight of Their Interaction with Human Insulin.

Reaction of two equivalents of the bulky 1,3-bis(2,6-diethylphenyl)thiourea ligand (L) with MX (being M = Cu+, Ag+; and X = Cl-, Br-, I-) in acetonitrile afforded neutral complexes of the type [MXL2] [CuClL2].2CH3CN (1a); [CuBrL2].2CH3CN (1b); [CuIL2] (1c): [AgClL2] (2a); [AgBrL2] (2b) and [AgIL2] (2c). The two aromatic groups in free ligand were found to be trans with respect to the thiourea unit, which was a reason to link the ligand molecules via intermolecular hydrogen bonding. Intramolecular hydrogen bonding was observed in all metal complexes. The copper complexes 1a and 1b are acetonitrile solvated and show not only intra- but also intermolecular hydrogen bonding between the coordinated thiourea and the solvated acetonitrile molecules. Silver complexes reported here are the first examples of structurally characterized tricoordinated thiourea-stabilized monomeric silver(I) halides. Molecular docking studies were carried out to analyze the binding modes of the metal complexes inside the active site of the human insulin (HI) protein. Analysis of the docked conformations revealed that the electrostatic and aromatic interactions of the protein N-terminal residues (i.e., Phe and His) may assist in anchoring and stabilizing the metal complexes inside the active site. According to the results of docking studies, the silver complexes exhibited the strongest inhibitory capability against the HI protein, which possesses a deactivating group, directly bonded to silver. All compounds were fully characterized by elemental analysis, NMR spectroscopy, and molecular structures of the ligand, and five out of six metal complexes were also confirmed by single-crystal X-ray diffraction.

Nestlike Silver(I) Thiolate Clusters with Tunable Emission Color Templated by Heteroanions.

Four silver thiolate clusters, [H3 O][(Ag3 S3 )(BF4 )@Ag27 (tBuS)18 (hfac)6 H2 O]⋅H2 O (1; hfac = hexafluoroacetylacetone), [(Ag3 S3 )(CF3 CO2 )@Ag30 (tBuS)16 (CF3 CO2 )9 (CH3 CN)4 ]⋅CF3 CO2 ⋅4 CH3 CN (2), [(Ag3 S3 )(MoO4 )@Ag30 (tBuS)16 (CF3 CO2 )9 (CH3 CN)4 ]⋅2 CH3 CN (3), and [(Ag3 S3 )(CrO4 )@Ag30 (tBuS)16 (CF3 CO2 )9 (CH3 CN)4 ]⋅4 CH3 CN (4), were isolated. They have similar nestlike structures assembled by an [Ag3 S3 ]3- template together with one of the BF4 - , CF3 CO2 - , MoO4 2- , or CrO4 2- anions. Interestingly, the solid-state emissions of 2-4 are dependent on the templating anions and are tunable from green to orange and then to red by changing the template from CF3 CO2 - to MoO4 2- and to CrO4 2- , and this may be correlated to the charge transfer between these templates to metal atoms. This work helps to understand the templating role of heteroanions and the relationship between structure and properties.

Cooperative Ligands in Dissolution of Gold.

Development of new, environmentally benign dissolution methods for metallic gold is driven by needs in the circular economy. Gold is widely used in consumer electronics, but sustainable and selective dissolution methods for Au are scarce. Herein, we describe a quantitative dissolution of gold in organic solution under mild conditions by using hydrogen peroxide as an oxidant. In the dissolution reaction, two thiol ligands, pyridine-4-thiol and 2-mercaptobenzimidazole, work in a cooperative manner. The mechanistic investigations suggest that two pyridine-4-thiol molecules form a complex with Au0 that can be oxidized, whereas the role of inexpensive 2-mercaptobenzimidazole is to stabilize the formed AuI species through a ligand exchange process. Under optimized conditions, the reaction proceeds vigorously and gold dissolves quantitatively in two hours. The demonstrated ligand-exchange mechanism with two thiols allows to drastically reduce the thiol consumption and may lead to even more effective gold dissolution methods in the future.

Cluster From Cluster: A Quantitative Approach to Magic Gold Nanoclusters [Au25 (SR)18 ].

High-yield and large-scale synthesis are highly demanded for the studies of gold nanoclusters. We developed a "cluster from cluster" approach to assemble gold nanoclusters with preformed atomically precise Au13 precursors. This facile approach has proved to be very effective in the synthesis of the well-known magic cluster [Au25 (SR)18 ]- , which could prepare the target cluster in high yield (overall yield up to ≈100 %) at large scale (gram-scale based on gold). This method can be applied in the synthesis of 10 Au25 clusters with different R groups. This work presents an important approach that may be extended to high-yield and large-scale synthesis of other metal nanoclusters.

Atomically Precise Gold Nanoclusters as Model Catalysts for Identifying Active Sites for Electroreduction of CO2.

Accurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic-level identification of active sites using atomically well-defined gold nanoclusters (Au NCs) Au25 , Au38 , and Au144 as model catalysts in the electrochemical CO2 reduction reaction (CO2 RR). The studied Au NCs exhibited remarkably high CO2 RR activity, which increased with increasing NC size. Electrochemical and X-ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO2 RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d-states for dethiolated Au sites. The structure-activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO2 RR activity was determined by the number of active sites on the cluster surface.

Silver-Sulfur Hybrid Supertetrahedral Clusters: The Hitherto Missing Members in the Metal-Chalcogenide Tetrahedral Clusters.

The synthesis of Group 11 metal chalcogenide supertetrahedral clusters (SCs) still remains a great challenge mainly due to the high tendency of metal aggregation through metallophilicity and global charge balance. Demonstrated herein are the preparation, crystallographic characterization, and optical properties of two stable silver-sulfur SCs through ligand-control; one as a discrete zero-dimensional (0D) V3,4-type cluster and the other as a one-dimensional (1D) zigzag chain extended by alternating V3,2-type clusters. The notation Vn,m (where n is the number of metal layers, and m is the number of vacant corners) is used to describe a new series of vacant-corner SCs, which can be derived from the regular Tn clusters. The existence of vacant-corner-type SCs may be ascribed to the low valence and tri-coordinated environment of silver ions. These are the first representatives of structurally determined silver-sulfur tetrahedral clusters thus far. This work enriches the coinage-metal chalcogenide tetrahedral cluster portfolio, discovers vacant-corner SCs present in silver-sulfur hybrid tetrahedral clusters, and provides effective means for further development of Group 11 coinage-metal chalcogenide SCs.

Manipulation of Inorganic Atomic-Layer Networks by Solution-Phase Co-assembly.

Homogeneous 2D lamellar assemblies of AuI thiolate coordination polymer (ATCP) were obtained by two-ligand co-assembly. The orbital levels and the bandgap of the 2D AuI -S network in the centre of the lamellae can be continuously tuned by means of the capping ligands on both sides, to give a new type of inorganic-organic composite semiconductor, the band structure of which can be easily tuned by low-temperature solution-phase co-assembly. Furthermore, the chemical reactivity of these ATCP co-assemblies also proved to be strongly dependent on the organic substituents, with well-tuneable transformation rates to gold nanoparticles. Apparently, this is the first work to demonstrate how organic substituents can continuously tune the electron band structure and chemical reactivity of inorganic atomic layers of semiconductor through co-assembly.

Role of Halide Ions in the Nature of the Magnetic Anisotropy in Tetrahedral CoII Complexes.

A series of mononuclear tetrahedral CoII complexes with a general molecular formula [CoL2 X2 ] [L=thiourea and X=Cl (1), Br (2) and I (3)] were synthesized and their structures were characterized by single-crystal X-ray diffraction. Direct-current (dc) magnetic susceptibility [χM T(T) and M(H)] and its slow relaxation of magnetization were measured for all three complexes. The experimental dc magnetic data are excellently reproduced by fitting both χM T(T) and M(H) simultaneously with the parameters D=+10.8 cm-1 , g1 =2.2, g2 =2.2, and g3 =2.4 for 1; D=-18.7 cm-1 , giso =2.21 for 2; and D=-19.3 cm-1 , giso =2.3 for 3. The replacement of chloride in 1 by bromide or iodide (in 2 and 3, respectively) was accompanied by a change in both sign and magnitude of the magnetic anisotropy D. Field-induced out-of-phase susceptibility signals observed in 10 % diluted samples of 1-3 imply slow relaxation of magnetization of molecular origin. To better understand the magnetization relaxation dynamics of complexes 1-3, detailed ab initio CASSCF/NEVPT2 calculations were performed. The computed spin Hamiltonian parameters are in good agreement with experimental data. In particular, the calculations unveil the role of halide ions in switching the sign of D on moving from Cl- to I- . The large spin-orbit coupling constant associated with the heavier halide ion and weaker π donation reduces the ground state-excited state gap, which leads to a larger contribution to negative D for complex 3 compared to complex 1. Further magnetostructural D correlations were developed to understand the role of structural distortion in the sign and magnitude of D values in this family of complexes.

Molecular ReI Cages: Structural and Luminescent Properties.

Versatile building block [{Re(CO)4 }3 (C3 N3 S3 )] (1 a; C3 N3 S3 =cyanurate trianion) reacts with linear dipyridyl ligands [i.e., pyrazine (pz), 4,4'-bipyridine (bpy), 1,2-bis(4-pyridyl)ethylene (bpe), bis(4-pyridyl)acetylene (bpa), and 1,4-bis(pyridyl-4-ylethynyl)benzene (bpb)] and a tripyridyl ligand [1,3,5-tris(4-pyridylethynyl)benzene (tpb)] to afford a series of molecular cages [{Re(CO)3 }6 (L)3 (C3 N3 S3 )2 ] [L=pz (2), bpy (3), bpe (4), bpa (5), bpb (6)] and [{Re(CO)3 }9 (tpb)3 (C3 N3 S3 )3 ] (7) under solvothermal conditions. Various structural dimensions and motifs can be systematically tuned and obtained by using different dipyridyl and tripyridyl ligands in the reactions. The molecular cages of hexanuclear complexes 2-6 containing dipyridyl ligands feature interesting trigonal-prismatic structures with different dimensions. Furthermore, nonanuclear complex 7 has a novel triangular-star structure, and three benzene rings of tpb ligands form a triple-decker arrangement with significant π⋅⋅⋅π interactions having distances of 3.490(1) and 3.528(1) Å. In addition, molecular cages 1-3 and 5-7 exhibit luminescence in the solid state, and their luminescent properties were also studied.

Heterocyclic Bismuth(III) Dithiocarbamato Complexes as Single-Source Precursors for the Synthesis of Anisotropic Bi2 S3 Nanoparticles.

New complexes catena-(µ2 -nitrato-O,O')bis(piperidinedithiocarbamato)bismuth(III) (1) and tetrakis(µ-nitrato)tetrakis[bis(tetrahydroquinolinedithiocarbamato)bismuth(III)] (2) were synthesised and characterised by elemental analysis, FTIR spectroscopy and thermogravimetric analysis. The single-crystal X-ray structures of 1 and 2 were determined. The coordination numbers of the Bi(III) ion are 8 for 1 and ≥6 for 2 when the experimental electron density for the nominal 6s(2) lone pair of electrons is included. Both complexes were used as single-source precursors for the synthesis of dodecylamine-, hexadecylamine-, oleylamine and tri-n-octylphosphine oxide-capped Bi2 S3 nanoparticles at different temperatures. UV/Vis spectra showed a blueshift in the absorbance band edge characteristic of a quantum size effect. High-quality, crystalline, long and short Bi2 S3 nanorods were obtained depending on the thermolysis temperature, which was varied from 190 to 270 °C. A general trend of increasing particle breadth with increasing reaction temperature and increasing length of the carbon chain of the amine (capping agent) was observed. Powder XRD patterns revealed the orthorhombic crystal structure of Bi2 S3 .

Designing Tunable White-Light Emission from an Aurophilic Cu(I) /Au(I) Coordination Polymer with Thioether Ligands.

White-light emitters have attracted considerable attention due to their importance in current and future technologies. By incorporating molecular fragments that independently emit in the blue, green/yellow, and red visible regions, specifically Cu-NC, Au⋅⋅⋅Au interactions, and Cu-SR2 , respectively, into a single material, new white-light-emitting systems have been targeted. With this goal, three new Cu(I) /thioether-based coordination polymers containing bridging [Au(CN)2 ](-) units have been synthesized and structurally characterized, and their photoluminescence properties (at room and low temperatures) have been delineated. Using this approach, white-light emission (tunable from slightly yellow to slightly blue, depending on λex ) is generated from Cu(Me2 S)[Au(CN)2 ], a feature uncommon in such simple coordination compounds.

Metallosupramolecular Structures Derived from a Series of Diphosphine-bridged Digold(I) Metalloligands with Terminal d-Penicillamine.

In this report, we describe our recent work on the development of a new family of chiral heteroleptic digold(I) metalloligands with mixed diphosphine and d-penicillaminate (d-pen), [Au2 (dppx)(d-pen-S)2 ](2-) (dppx = PPh2 (CH2 )n PPh2 , n = 1-5) and their application for the construction of chiral multinuclear and metallosupramolecular structures. The reactions of the metalloligands with 3d metal ions produce a variety of chiral heterobimetallic structures retaining the digold(I) metalloligand structure, ranging from discrete trinuclear to infinite helix structures that depend on the type of dppx. In addition, monophosphine and triphosphine analogues of the metalloligands were designed, and their coordination behavior is discussed to show the essential properties and potential extensibility of this class of metalloligands.

Extending the Substrate Scope for the Asymmetric Iridium-Catalyzed Hydrogenation of Minimally Functionalized Olefins by Using Biaryl Phosphite-Based Modular Ligand Libraries.

Asymmetric hydrogenation is one of the most efficient and atom-economical tools to prepare chiral molecules. However, the enantiodiscrimination of simple, minimally functionalized olefins is still challenging and requires more sophisticated ligand design. Herein, we discuss our progress in the successful development of ligand design for the iridium-catalyzed asymmetric hydrogenation of minimally functionalized olefins.

A reversible proton relay process mediated by hydrogen-bonding interactions in [FeFe]hydrogenase modeling.

A reversible and temperature-dependent proton-relay process is demonstrated for a Fe2 complex possessing a terminal thiolate in the presence of nitrogen-based acids. The terminal sulfur site (S(t) ) of the complex forms a hydrogen-bond interaction with N,N-dimethylanilinium acid at 183 K. The Fe2 core, instead, is protonated to generate a bridging hydride at 298 K. Reversibility is observed for the tautomerization between the hydrogen-bonded pair and the Fe-hydride species. X-ray structural analysis of the hydrogen-bonded species at 193 K reveals a short N(H)⋅⋅⋅S(t) contact. Employment of pyridinium acid also results in similar behavior, with reversible proton-hydride interconversion. DFT investigation of the proton-transfer pathways indicates that the pKa value of the hydrogen-bonded species is enhanced by 3.2 pKa units when the temperature is decreased from 298 K to 183 K.

Towards Structural-Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex.

The synthesis and characterization of a biomimetic system that can reversibly bind acetylene (ethyne) is reported. The system has been designed to mimic catalytic intermediates of the tungstoenzyme acetylene hydratase. The thiophenyloxazoline ligand S-Phoz (2-(4',4'-dimethyloxazolin-2'-yl)thiophenolate) is used to generate a bioinspired donor environment around the W center, facilitating the stabilization of W-acetylene adducts. The featured complexes [W(C2 H2 )(CO)(S-Phoz)2 ] (2) and [WO(C2 H2 )(S-Phoz)2 ] (3) are extremely rare from a synthetic and structural point of view as very little is known about W-C2 H2 adducts. Upon exposure to visible light, 3 can release C2 H2 from its coordination sphere to yield the 14-electron species [WO(S-Phoz)2 ] (4). Under light-exclusion 4 re-activates C2 H2 making this the first fully characterized system for the reversible activation of acetylene.

pH-controlled multiple chiral inversion that induces molecular dimerization in a gold(I)-cobalt(III) coordination system with L-cysteinate.

Herein, a unique coordination system that exhibits multiple chiral inversions and molecular dimerization in response to a subtle pH change is reported. Treatment of (Δ)2-H3[Au3Co2(L-cys)6] (H3[1 a]) with [Co3(aet)6](NO3)3 (aet=2-aminoethanethiolate) in water at pH 7 gave a 1:1 complex salt of [Co3(aet)6](3+) and [1 a](3-), retaining the Au(I)3Co(III)2 structure and chiral configurations of [1 a](3-). Similar treatment at pH 9 led to not only the inversion of all of the chiral Co(III) and S centers but also the dimerization of [1 a](3-), giving a 2:1 complex salt of [Co3(aet)6](3+) and (Λ)4(R)12-[Au6Co4(L-cys)12](6-) ([2](6-)). When dissociated from [Co3(aet)6](3+) in solution, [2](6-) was converted to (Λ)2(R)6-[Au3Co2(L-cys)6](3-) ([1 b](3-)) with retention of the chiral configurations.

Phosphinothiolates as ligands for polyhydrido copper nanoclusters.

The reaction of [CuI(HSC6 H4 PPh2 )]2 with NaBH4 in CH2 Cl2 /EtOH led to air- and moisture-stable copper hydride nanoparticles (CuNPs) containing phosphinothiolates as new ligands, one of which was isolated by crystallization. The X-ray crystal structure of [Cu18 H7 L10 I] (L=(-) S(C6 H4 )PPh2 ) shows unprecedented features in its 28-atom framework (18 Cu and 10 S atoms). Seven hydrogen atoms, in hydride form, are needed for charge balance and were located by density functional theory methods. H2 was released from the copper hydride nanoparticles by thermolysis and visible light irradiation.