Fluxional Behavior Research Articles

Computational Studies of Molybdenum-Containing Metal–Sulfur and Metal–Hydride Clusters

The development of transition metal clusters is an active area of research in inorganic chemistry, as they can be used as catalysts to perform chemically or biologically relevant reactions. Computational chemistry, employing density functional theory (DFT), plays a key role in rationalizing the electronic structure and properties of transition metal clusters. This article reviews recent quantum chemical studies of Mo3S4M clusters (M = Fe, Co, Ni), their CO- or N2-bound variants, and metal–hydride clusters. The ground state of the cluster systems was computed, and properties such as metal–metal bonding, orbital interactions, fluxional behavior of ligands, spectroscopy, and reaction mechanisms were rationalized and compared with available experimental results. Our research findings evidence that computational studies employing quantum chemical methods can guide experimental researchers to develop novel transition metal clusters for potential applications in catalysis.

Dual structural fluxionality in the copper borozene complex Cu3B8-: A two-layered molecular rotor.

Doubly aromatic B82-, a borozene analog of benzene (C6H6) due to their similar π bonding, can be considered an ideal base for multi-layered molecular rotors. Here, we theoretically constructed the copper borozene complex Cu3B8- to investigate its stability and structural fluxionality. The lowest energy isomers consist of two-layered configurations: a B8 molecular wheel and a triangular Cu3 motif that either stands upright or lies flat above the B8 wheel. Both configurations exhibit structural fluxionality, as indicated by the free rotation of Cu3 with respect to the B8 molecular wheel, confirmed by Born-Oppenheimer molecular dynamics simulations even at low temperatures. This fluxional behavior is associated with an ultra-soft vibrational mode of Cu3 (less than 10.0cm-1) and a negligible rotational barrier of 0.01 kcal/mol. Notably, high simulated temperatures cause irregular interconversion between the standing and lying orientations of Cu3 without regularity. Chemical bonding analysis confirmed that charge transfer from Cu3 to the B8 wheel renders Cu3B8- a typical copper borozene complex, [Cu3+][B82-], where B82- has six delocalized π and σ electrons. This electron delocalization contributes to a dilute and continuous electron cloud that underpins the dynamic behavior of the Cu3 trimer.

Correction: Synthesis, Structure and Fluxional Behaviour of Sulfido- Capped Triruthenium Clusters Containing a Bridging 1,1’-Bis(diphenylphosphino)ferrocene Ligand

Correction: Synthesis, Structure and Fluxional Behaviour of Sulfido- Capped Triruthenium Clusters Containing a Bridging 1,1’-Bis(diphenylphosphino)ferrocene Ligand

Molecular Ball Joints: Mechanochemical Perturbation of Bullvalene Hardy-Cope Rearrangements in Polymer Networks.

The solution-state fluxional behavior of bullvalene has fascinated physical organic and supramolecular chemists alike. Little effort, however, has been put into investigating bullvalene applications in bulk, partially due to difficulties in characterizing such dynamic systems. To address this knowledge gap, we herein probe whether bullvalene Hardy-Cope rearrangements can be mechanically perturbed in bulk polymer networks. We use dynamic mechanical analysis to demonstrate that the activation barrier to the glass transition process is significantly elevated for bullvalene-containing materials relative to "static" control networks. Furthermore, bullvalene rearrangements can be mechanically perturbed at low temperatures in the glassy region; such behavior facilitates energy dissipation (i.e., increased hysteresis energy) and polymer chain alignment to stiffen the material (i.e., increased Young's modulus) under load. Computational simulations corroborate our work that showcases bullvalene as a reversible "low-force" covalent mechanophore in the modulation of viscoelastic behavior.

Tri and hexaosmium clusters bearing saccharinate and diphosphine ligands: Synthesis, structure and fluxionality

The reactivity of saccharinate-bridged triosmium cluster [Os3(CO)10(μ-H)(μ-sac)] (1) with two diphosphines namely bis(diphenylphosphino)methane (dppm) and 1,1′-bis(diphenylphosphino)ferrocene (dppf) have been investigated. Cluster 1 reacts with dppm in refluxing toluene to yield triosmium [Os3(CO)9(κ1-dppm)(μ-H)(μ-sac)] (2), [Os3(CO)9(κ1-dppm)(μ-H)(μ-sac)] (3) and [Os3(CO)8(µ-dppm)(μ-H)(µ-sac)] (4) along with the hexaosmium [{Os3(CO)9(μ-H)(µ-sac)}2(κ2-dppm)] (5). The dppm ligand acts as a monodentate ligand in 2 and 3 by coordinating to a single osmium, while it bridges an osmium-osmium edge in 4 and connects to triosmium units in 6. A similar reaction with dppf furnishes [Os3(CO)9(κ1-dppf)(μ-H)(μ-sac)] (6), [Os3(CO)8(µ-dppf)(μ-H)(μ-sac)] (7) and [{Os3(CO)9(μ-H)(µ-sac)}2(κ2-dppf)] (8) which are dppf analogues of 3–5, respectively. Control experiments confirms that 3 is the precursor of 4 and 5, while 6 is the precursor of 7 and 8. All the products are formed via substitution of carbonyl by the diphosphine, and have been characterized by analytical and spectroscopic data. The molecular structures of 2 and 4–7 have been determined by X-ray crystallography. Cluster 7 shows fluxional behavior in solution at room temperature, and its fluxionality has been probed by VT NMR experiments.

Single-Crystal X-ray Structure Determination of Tris(pyrazol-1-yl)methane Triphenylphosphine Copper(I) Tetrafluoroborate, Hirshfeld Surface Analysis and DFT Calculations

The tetrafluoroborate salt of the cationic Cu(I) complex [Cu(CHpz3)(PPh3)]+, where CHpz3 is the tridentate N-donor ligand tris(pyrazol-1-yl)methane and PPh3 is triphenylphosphine, was synthesized through a displacement reaction on the acetonitrile complex [Cu(NCCH3)4][BF4]. The compound crystallizes in the monoclinic P21/c space group. The single-crystal X-ray diffraction revealed that the copper(I) centre is tetracoordinated, with a disposition of the donor atoms surrounding the metal centre quite far from the ideal tetrahedral geometry, as confirmed by continuous shape measures and by the τ4 parameter. The intermolecular interactions at the solid state were investigated through the Hirshfeld surface analysis, which highlighted the presence of several non-classical hydrogen bonds involving the tetrafluoroborate anion. The electronic structure of the crystal was modelled using plane-wave DFT methods. The computed band gap is around 2.8 eV and separates a metal-centred valence band from a ligand-centred conduction band. NMR spectroscopy indicated the fluxional behaviour of the complex in CDCl3 solution. The geometry of the compound in the presence of chloroform as implicit solvent was simulated by means of DFT calculations, together with possible mechanisms related to the fluxionality. The reversible dissociation of one of the pyrazole rings from the Cu(I) coordination sphere resulted in an accessible process.

Amidinatotetrylenes Donor Functionalized on Both N Atoms: Structures and Coordination Chemistry.

E(hmds)(bqfam) (E = Ge (1a), Sn (1b); hmds = N(SiMe3)2, bqfam = N,N'-bis(quinol-8-yl)formamidinate), which are amidinatotetrylenes equipped with quinol-8-yl fragments on the amidinate N atoms, have been synthesized from the formamidine Hbqfam and Ge(hmds)2 or SnCl(hmds). Both 1a and 1b are fluxional in solution at room temperature, as the E atom oscillates from being attached to the two amidinate N atoms to being chelated by an amidinate N atom and its closest quinolyl N atom (both situations are similarly stable according to density functional theory calculations). The hmds group of 1a and 1b is still reactive and the deprotonation of another equivalent of Hbqfam can be achieved, allowing the formation of the homoleptic derivatives E(bqfam)2 (E = Ge, Sn). The reactions of 1a and 1b with [AuCl(tht)] (tht = tetrahydrothiophene), [PdCl2(MeCN)2], [PtCl2(cod)] (cod = cycloocta-1,5-diene), [Ru3(CO)12] and [Co2(CO)8] have been investigated. The gold(I) complexes [AuCl{κE-E(hmds)(bqfam)}] (E = Ge, Sn) have a monodentate κE-tetrylene ligand and display fluxional behavior in solution the same as that of 1a and 1b. However, the palladium(II) and platinum(II) complexes [MCl{κ3E,N,N'-ECl(hmds)(bqfam)}] (M = Pd, Pt; E = Ge, Sn) contain a κ3E,N,N'-chloridotetryl ligand that arises from the insertion of the tetrylene E atom into an M-Cl bond and the coordination of an amidinate N atom and its closest quinolyl N atom to the metal center. Finally, the binuclear ruthenium(0) and cobalt(0) complexes [Ru2{μE-κ3E,N,N'-E(hmds)(bqfam)}(CO)6] and [Co2{μE-κ3E,N,N'-E(hmds)(bqfam)}(μ-CO)(CO)4] (E = Ge, Sn) have a related κ3E,N,N'-tetrylene ligand that bridges two metal atoms through the E atom. For the κ3E,N,N'-metal complexes, the quinolyl fragment not attached to the metal is pendant in all the germanium compounds but, for the tin derivatives, is attached to (in the Pd and Pt complexes) or may interact with (in the Ru2 and Co2 complexes) the tin atom.

Tuning the Softness of the Pendant Arms and the Polyazamacrocyclic Backbone to Chelate the 203Pb/212Pb Theranostic Pair.

A series of macrocyclic ligands were considered for the chelation of Pb2+: 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), 1,7-bis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane-4,10-diacetic acid (DO2A2S), 1,5,9-tris[2-(methylsulfanyl)ethyl]-1,5,9-triazacyclododecane (TACD3S), 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetrazacyclotridecane (TRI4S), and 1,4,8,11-tetrakis[2-(methylsulfanyl)ethyl]-1,4,8,11-tetrazacyclotetradecane (TE4S). The equilibrium, the acid-mediated dissociation kinetics, and the structural properties of the Pb2+ complexes formed by these chelators were examined by UV-Visible and nuclear magnetic resonance (NMR) spectroscopies, combined with potentiometry and density functional theory (DFT) calculations. The obtained results indicated that DO4S, DO3S, DO3SAm, and DO2A2S were able to efficiently chelate Pb2+ and that the most suitable macrocyclic scaffold for Pb2+ is 1,4,7,10-tetrazacyclododecane. NMR spectroscopy gave insights into the solution structures of the Pb2+ complexes, and 1H-207Pb interactions confirmed the involvement of S and/or O donors in the metal coordination sphere. Highly fluxional solution behavior was discovered when Pb2+ was coordinated to symmetric ligands (i.e., DO4S and DO2A2S) while the introduction of structural asymmetry in DO3S and DO3SAm slowed down the intramolecular dynamics. The ligand ability to chelate [203Pb]Pb2+ under highly dilute reaction conditions was explored through radiolabeling experiments. While DO4S and DO3S possessed modest performance, DO3SAm and DO2A2S demonstrated high complexation efficiency under mild reaction conditions (pH = 7, 5 min reaction time). The [203Pb]Pb2+ complexes' integrity in human serum over 24 h was appreciably good for [203Pb][Pb(DO4S)]2+ (80 ± 5%) and excellent for [203Pb][Pb(DO3SAm)]2+ (93 ± 1%) and [203Pb][Pb(DO2A2S)] (94 ± 1%). These results reveal the promise of DO2A2S and DO3SAm as chelators in cutting-edge theranostic [203/212Pb]Pb2+ radiopharmaceuticals.

Support effects on conical intersections of Jahn-Teller fluxional metal clusters on the sub-nanoscale.

The concept of fluxionality has been invoked to explain the enhanced catalytic properties of atomically precise metal clusters of subnanometer size. Cu3 isolated in the gas phase is a classical case of a fluxional metal cluster where a conical intersection leads to a Jahn-Teller (JT) distortion resulting in a potential energy landscape with close-lying multiminima and, ultimately, fluxional behavior. In spite of the role of conical intersections in the (photo)stability and (photo)catalytic properties of surface-supported atomic metal clusters, they have been largely unexplored. In this work, by applying a high-level multi-reference ab initio method aided with dispersion corrections, we analyze support effects on the conical intersection of Cu3 considering benzene as a model support molecule of carbon-based surfaces. We verify that the region around the conical intersection and the associated Jahn-Teller (JT) distortion is very slightly perturbed by the support when the Cu3 cluster approaches it in a parallel orientation: Two electronic states remain degenerate for a structure with C3 symmetry consistent with the D3h symmetry of unsupported Cu3 at the conical intersection. It extends over a one-dimensional seam that characterizes a physisorption minimum of the Cu3-benzene complex. The fluxionality of the Cu3 cluster, reflected in large fluctuations of relaxed Cu-Cu distances as a function of the active JT mode, is kept unperturbed upon complexation with benzene as well. In stark contrast, for the energetically favored perpendicular orientation of the Cu3 plane to the benzene ring plane, the conical intersection (CI) is located 12 100 cm-1 (∼1.5 eV) above the chemisorption minimum, with the fluxionality being kept at the CI's nearby and lost at the chemisorption well. The first excited state at the perpendicular orientation has a deep well (>4000 cm-1), being energetically closer to the CI. The transition dipole moment between ground and excited states has a significant magnitude, suggesting that the excited state can be observed through direct photo-excitation from the ground state. Besides demonstrating that the identity of an isolated Jahn-Teller metal cluster can be preserved against support effects at a physisorption state and lifted out at a chemisorption state, our results indicate that a correlation exists between conical intersection topography and fluxionality in the metal cluster's Cu-Cu motifs.

Discovering SnB7-: a half-sandwich structure with double aromaticity and pathways to molecular machines.

Numerous boron-based molecular fluxional models, such as the Wankel motor, tank treads B11- and B10C, and the Earth-Moon system Be6B11-, have been widely recognized for their potential to develop molecular machines. From a series of tin-doped boron clusters SnBn- (n = 5-14), the half-sandwich structure SnB7- is found to possess high relative energy stability, and a HOMO-LUMO gap of 4.33 eV. This structure exhibits valence electron orbitals reminiscent of σ-π double aromatic compounds. The incorporation of tin effectively fills the doubly vacant π orbitals of its parent triplet B7-, thereby enhancing both magnetic shielding capabilities and range. Thermal bath tests demonstrate its significant dynamic stability, as the kinetic energy provided by thermal baths below 3800 K remains insufficient to disrupt its inherent elasticity. Additionally, transition state searches and intrinsic reaction coordinate analyses confirm that the tin atom migrates from the centre to the edge of the boron ligand surface, a phenomenon that can be observed in high-temperature thermal bath simulations. This fluxional behaviour provides insights for constructing novel molecular machine models.

IPr*Thia - wingtip-flexible, sterically hindered, modular, N,C/S,C-chelating thiazole-donor N-heterocyclic carbene ligands.

N-Heterocyclic carbenes (NHCs) represent a pivotal class of ligands in coordination chemistry owing to their unique electronic properties. In particular, hemilabile N-heterocyclic carbenes have garnered significant attention over the past decade due to their capacity to transiently coordinate to metals and open coordination sites. However, hemilabile NHC ligands have been predominantly limited to N, O and P donors, while NHC ligands bearing versatile S-donors have been severely underdeveloped. Herein, we report wingtip-flexible, sterically hindered NHC ligands that feature N,C/S,C-chelating thiazole donors in combination with the powerful IPr* (IPr* = (2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) scaffold. These ligands are prepared using a highly modular SNAr arylation of thiazole derivatives. Full structural and electronic characterization is reported. The ligands feature a high barrier to rotation around the N-thiazole axis (10 kcal mol-1). The ligands are evaluated for their steric, electron-donating and π-accepting properties as well as coordination chemistry to Ag(I), Pd(II), Rh(I) and Se. Preliminary studies on Ag, Pd and Rh catalysis are presented. The efficiency of the approach is highlighted by preparing a library of unsymmetrical imidazolium precursors. The mono-IPr* wingtip provides a highly hindered yet sterically flexible environment adjusting to metal centers, while the N-thiazolyl wingtip displays a fluxional behavior that interchanges from the hard/soft N,C to soft/soft S,C coordination. Considering the importance of hemilabile N-heterocyclic carbene ligands in metal stabilization in inorganic and organometallic chemistry, we expect that this class of ligands will be of broad interest.

Synthesis, antioxidant and structural properties of modified ebselen derivatives and conjugates.

Ebselen is a drug in clinical trials for several diseases and degenerative conditions where oxidative stress is implicated. A series of novel ebselen analogues was synthesized, including hydroxy-, alkoxy- and aminomethylene derivatives, as well as hybrid species where the ebselen selenium atom is shared with other potent antioxidant structures, such as cyclic selenenyl sulfide, cyclic seleninate ester and spirodioxyselenurane moieties. Conjugates of ebselen with cholesterol, prednisolone and the radical inhibitor BHT were also prepared. The products were tested for antioxidant activity in an NMR-based assay by measuring the rate of consumption of benzyl thiol or the production of dibenzyl disulfide in the presence of hydrogen peroxide when catalyzed by the ebselen analogues. Activities ranged from 12 to 0.12 times that of ebselen. The oxidation of the 2-hydroxymethylene derivative of ebselen was faster than thiolysis in the initial step and the overall rate was further accelerated under basic conditions. The corresponding selenenyl sulfide analogue underwent very slow disproportionation under neutral conditions that was enhanced by the presence of a base catalyst. During investigation of possible fluxional behaviour of a bis-amide analogue, an unusual tetraphenyphosphonium salt of a tricoordinate selenium pincer anion was discovered with exceptionally potent catalytic activity, 130 times that of ebselen. In addition to rate measurements, X-ray crystallography and DFT computational methods were also employed to gain further structural and mechanistic insights.

Aluminium complexes of phenoxy-azo ligands in the catalysis of rac-lactide polymerisation.

Fourteen new phenoxy-azo aluminium complexes comprising two series, namely, dimethyl{phenoxy-azo}aluminium complexes 1a-7a and monomethyl{phenoxy-azo}aluminium complexes 1b-7b, were successfully synthesised and characterised. The molecular structure of complex 4a, determined using X-ray diffraction analysis, displayed a distorted tetrahedral geometry. The 1H NMR spectrum of complex 5b revealed fluxional behaviour caused by isomeric transformation that occurs in the solution at room temperature. The activation parameters determined by lineshape analysis of variable-temperature 1H NMR spectra in toluene-d8 are as follows: ΔH‡ = 70.05 ± 1.19 kJ mol-1, ΔS‡ = 21.78 ± 3.58 J mol-1 K-1 and ΔG‡ (298 K) = 63.56 ± 0.11 kJ mol-1. All aluminium complexes are active initiators for the ring-opening polymerisation of rac-lactide, and the polymerisations proceeded in a controlled manner and were living. In comparison, the catalytic activity of the dimethyl{phenoxy-azo}aluminium complexes was insignificantly different from that of the corresponding monomethyl{phenoxy-azo}aluminium complexes. The steric factor of the ortho-phenoxy substituent was observed to exert a decelerating effect on the catalytic rate. Kinetic investigations revealed first-order dependency on both monomer and initiator concentrations. Comparative catalytic investigations conducted on phenoxy-azo aluminium and phenoxy-imine aluminium complexes revealed that the former complexes exhibited lower catalytic activity.

Ligand-free supermolecules: [Pd2@Ge18]4- and [Pd2@Sn18]4- as multiple-bonded Zintl-ion clusters based on Pd@Ge9 and Pd@Sn9 assembled units.

Understanding intercluster bonding interactions is important in the rational synthesis of building blocks for molecular materials. Such characteristics have been developed for coinage metal clusters resembling single-, double-, and triple-bonded species, coined as supermolecules. Herein, we extend such an approach for understanding main-group clusters, thus evaluating [Pd2@E18]4- clusters (E = Ge, Sn) involving the fusion of parent spherical aromatic [Pd@E12]2- building units. Our results indicate intercluster bonding provided by contribution from 2P and 1G shells centered at each building motif, leading to an overall bond order of 2.70 and 2.31 for [Pd2@Ge18]4- and [Pd2@Sn18]4-, respectively. In addition, 119Sn-NMR patterns were evaluated to complement the experimental characterization of a single peak owing to the insolution fluxional behavior of [Pd2@Sn18]4- as three peaks owing to the three sets of unique Sn atoms within the structure. Magnetic response properties revealed that spherical aromatic characteristics from parent [Pd@E12]2- building units are retained in the overall [Pd2@E18]4- oblate cluster as two spherical aromatic units. Hence, the notion of superatomic molecules is extended to Zintl-ion clusters, favoring further rationalization for the fabrication of cluster-assembled solids.

Ultrasmall Pd Clusters in FER Zeolite Alleviate CO Poisoning for Effective Low-Temperature Carbon Monoxide Oxidation.

Ultrasmall Pd4 clusters form in the micropores of FER zeolite during low-temperature treatment (100 °C) in the presence of humid CO gas. They effectively catalyze CO oxidation below 100 °C, whereas Pd nanoparticles are not active as they are poisoned by CO. Using catalytic measurements, infrared (IR) spectroscopy, X-ray absorption spectroscopy (EXAFS), microscopy, and density functional theory calculations, we provide the molecular-level insight into this previously unreported phenomenon. Pd nanoparticles get covered with CO at low temperatures, which effectively blocks O2 activation until CO desorption occurs. Small Pd clusters in zeolites, in contrast, demonstrate fluxional behavior in the presence of CO, which significantly increases the affinity for binding O2. Our study provides a pathway to achieve low-temperature CO oxidation activity on the basis of a well-defined Pd/zeolite system.

Constrained Phosphine Chalcogenide Selenoethers Supported by peri-Substitution

A series of phosphorus and selenium peri-substituted acenaphthene species with the phosphino group oxidized by O, S, and Se has been isolated and fully characterized, including by single-crystal X-ray diffraction. The P(V) and Se(II) systems showed fluxional behavior in solution due to the presence of two major rotamers, as evidenced with solution NMR spectroscopy. Using Variable-Temperature NMR (VT NMR) and supported by DFT (Density Functional Theory) calculations and solid-state NMR, the major rotamers in the solid and in solution were identified. All compounds showed a loss of the through-space JPSe coupling observed in the unoxidized P(III) and Se(II) systems due to the sequestration of the lone pair of the phosphine, which has been previously identified as the major contributor to the coupling pathway.

Half‐Sandwich, Bent‐Sandwich and Triple‐Decker Molybdenum Complexes of S2N2 – Fluxionality and Metal‐Metal Bond

AbstractThe instability of the π‐complexes of electron‐rich inorganic aromatics with transition metal fragments, contrary to their conventional aromatic analogues, was investigated by taking the four‐membered 6π‐electron S2N2. Our theoretical investigation based on fragment molecular orbitals and Energy Decomposition Analysis with Natural Orbitals for Chemical Valence (EDA‐NOCV) on the bonding nature of different types of π‐complexes of S2N2 viz. half‐sandwich, bent‐sandwich and triple‐decker type complexes with molybdenum fragment reveals that S2N2 can potentially act as a six π‐electron donor. However, due to the lower energy π* MOs the π‐back donation from metal fragment is stronger than the π‐donation, which might lead to weaking of the overall ring structure and low dissociation energy. The dissociation energy for dissociation of one S2N2 ring increases with the increasing number of S2N2 in the complex. The smaller size of the ring leads to fluxional behaviour in order to attain orbital compatibility between the π‐MOs and the metal orbitals. Also, the triple decker complex depicts an unsymmetric middle deck, where the middle S2N2 ring has been fragmented into two SN units along with a Mo−Mo bond. The higher dissociation energy of triple‐decker complexes can be corroborated well with the report of an isoelectronic triple‐decker complex [Mo2Te12]6+.

Antifungal activity of Co(II) and Cu(II) complexes containing 1,3-bis(benzotriazol-1-yl)-propan-2-ol on the growth and virulence traits of fluconazole-resistant Candida species: synthesis, DFT calculations, and biological activity

Relevant virulence traits in Candida spp. are associated with dimorphic change and biofilm formation, which became an important target to reduce antifungal resistance. In this work, Co(II) complexes containing a benzotriazole derivative ligand showed a promising capacity of reducing these virulence traits. These complexes exhibited higher antifungal activities than the free ligands against all the Candida albicans and non-albicans strains tested, where compounds 2 and 4 showed minimum inhibitory concentration values between 15.62 and 125 μg mL−1. Moreover, four complexes (2–5) of Co(II) and Cu(II) with benzotriazole ligand were synthesized. These compounds were obtained as air-stable solids and characterized by melting point, thermogravimetric analysis, infrared, Raman and ultraviolet/visible spectroscopy. The analysis of the characterization data allowed us to identify that all the complexes had 1:1 (M:L) stoichiometries. Additionally, Density Functional Theory calculations were carried out for 2 and 3 to propose a probable geometry of both compounds. The conformer Da of 2 was the most stable conformer according to the Energy Decomposition Analysis; while the conformers of 3 have a fluxional behavior in this analysis that did not allow us to determine the most probable conformer. These results provide an important platform for the design of new compounds with antifungal activities and the capacity to attack other target of relevance to reduce antimicrobial resistance.

The Synthesis, Characterization, and Fluxional Behavior of a Hydridorhodatetraborane.

The octahydridotriborate anion plays a crucial role in the field of polyhedral boron chemistry, facilitating the synthesis of higher boranes and the preparation of diverse transition metal complexes. Among the stable forms of this anion, CsB3H8 (or (n-C4H9)4N)[B3H8] have been identified. These salts serve as valuable precursors for the synthesis of metallaboranes, wherein the triborate anion acts as a ligand coordinating to the metal center. In this study, we have successfully synthesized a novel rhodatetraborane dihydride, [Rh(η2-B3H8)(H)2(PPh3)2] (1), which represents a Rh(III) complex featuring a bidentate chelate ligand fasormed by B3H8-. Extensive characterization of this rhodatetraborane complex has been performed using NMR spectroscopy in solution and X-ray diffraction analysis in the solid state. Notably, the complex exhibits intriguing fluxional behavior, which has been investigated using NMR techniques. Moreover, we have explored the reactivity of complex 1 towards pyridine (py) and dimethylphenylphosphine (PMe2Ph). Our findings highlight the labile nature of this four-vertex rhodatetraborane as it undergoes disassembly upon attack from the corresponding Lewis base, resulting in the formation of borane adducts, LBH3, where L = py, PMe2Ph. Furthermore, in these reactions, we report the characterization of new cationic hydride complexes, such as [Rh(H)2(PPh3)2 (py)]+ (2) and [Rh(H)2(PMe2Ph)4]+. Notably, the latter complex has been characterized as the octahydridotriborate salt [Rh(H)2(PMe2Ph)4][B3H8] (3), which extends the scope of rhodatetraborane derivatives.

Synthesis of ruthenium carbonyl cluster complexes containing bis(2′-pyridylethynyl)benzene derivatives: Construction of an extended Zero-valent ruthenium chain

The reactions of Ru3(CO)12 in a refluxing acetonitrile-toluene solution with a half equivalent of the ligand 1,3-bis(pyridin-2-ylethynyl)benzene afforded Ru3(CO)7(μ-CO)[μ-(2-PyCCH)(1,3-C6H3)(2-PyCC)]Ru4(CO)12 (compound 1) and Ru3(CO)7(μ-CO)[μ-(2-PyCCH)(1,3-C6H2)(2-PyCCH)]Ru3(CO)8 (compound 2). Separately, Ru3(CO)12 was treated with a half equivalent of 1,4-bis(pyridin-2-ylethynyl)benzene in a refluxing acetonitrile-toluene solution to generate Ru3(CO)7(μ-CO)[μ-(2-PyCCH)(1,4-C6H3)(2-PyCC)]Ru4(CO)12 (compound 3) and Ru3(CO)8Ru(CO)2[μ-(2-PyCCH)(1,4-C6H2)(2-PyCCH)]Ru3(CO)8 (compound 4). Compounds 1–4 were characterized by FT-IR, NMR, ESI-HRMS and single-crystal X-ray diffraction. The structure of compound 2 was found to contain two triruthenium triangular frameworks, and compound 1 was found to be an intermediate of compound 2. Compounds 1 and 3 were shown to consist of triruthenium and tetraruthenium frameworks. Both compounds 1 and 3 exhibited two types of fluxional behavior in solution due to degenerate rearrangement of the acetylide ligand and restricted rotation. This assumption was confirmed by the variable-temperature 1H NMR, COSY and NOESY spectra. Noticeably, compound 4 possessed a quasilinear pentaruthenium structure, and compound 3 was shown to be an intermediate to compound 4.