Synthesis and Characterization of Mixed Chalcogen Triangular Complexes with New Mo3(μ3-S)(μ2-Se2)34+ and M3(μ3-S)(μ2-Se)34+(M = Mo, W) Cluster Cores

Unusual Square Pyramidal Chalcogenide Mo5 Cluster with Bridging Pyrazolate-Ligands

The family of chalcogenide molybdenum clusters is well presented in the literature by a series of compounds of nuclearity ranging from binuclear to multinuclear articulating octahedral fragments. Clusters actively studied in the last decades were shown to be promising as components of superconducting, magnetic, and catalytic systems. Here, we report the synthesis and detailed characterization of new and unusual representatives of chalcogenide clusters: square pyramidal complexes [{Mo₅(μ₃-Se)ⁱ₄(μ₄-Se)ⁱ(μ-pz)ⁱ₄}(pzH)^t₅]^1+/2+ (pzH = pyrazole, i = inner, t = terminal). Individually obtained oxidized (2+) and reduced (1+) forms have very close geometry (proven by single-crystal X-ray diffraction analysis) and are able to reversibly transform into each other, which was confirmed by cyclic voltammetry. Comprehensive characterization of the complexes, both in solid and in solution, confirms the different charge state of molybdenum in clusters (XPS), magnetic properties (EPR), and so on. DFT calculations complement the diverse study of new complexes, expanding the chemistry of molybdenum chalcogenide clusters.

Multimodal Structure Solution with 19F NMR Crystallography of Spin Singlet Molybdenum Oxyfluorides

Complex crystal structures with subtle atomic-scale details are now routinely solved using complementary tools such as X-ray and/or neutron scattering combined with electron diffraction and imaging. Identifying unambiguous atomic models for oxyfluorides, needed for materials design and structure-property control, is often still a considerable challenge despite their advantageous optical responses and applications in energy storage systems. In this work, NMR crystallography and single-crystal X-ray diffraction are combined for the complete structure solution of three new compounds featuring a rare triangular early transition metal oxyfluoride cluster, [Mo₃O₄F₉]^5-. After framework identification by single-crystal X-ray diffraction, 1D and 2D solid-state ¹⁹F NMR spectroscopy supported by ab initio calculations are used to solve the structures of K₅[Mo₃O₄F₉]·3H₂O (1), K₅[Mo₃O₄F₉]·2H₂O (2), and K₁₆[Mo₃O₄F₉]₂[TiF₆]₃·2H₂O (3) and to assign the nine distinct fluorine sites in the oxyfluoride clusters. Furthermore, ¹⁹F NMR identifies selective fluorine dynamics in K₁₆[Mo₃O₄F₉]₂[TiF₆]₃·2H₂O. These dual scattering and spectroscopy methods are used to demonstrate the generality and sensitivity of ¹⁹F shielding to small changes in bond length, on the order of 0.01 Å or less, even in the presence of hydrogen bonding, metal-metal bonding, and electrostatic interactions. Starting from the structure models, the nature of chemical bonding in the molybdates is explained by molecular orbital theory and electronic structure calculations. The average Mo-Mo distance of 2.505 Å and diamagnetism in 1, 2, and 3 are attributed to a metal-metal bond order of unity along with a 1a²1e⁴ electronic ground state configuration for the [Mo₃O₄F₉]^5- cluster, leading to a rare trimeric spin singlet involving d² Mo⁴⁺ ions. The approach to structure solution and bonding analysis is a powerful strategy for understanding the structures and chemical properties of complex fluorides and oxyfluorides.

Hemilability of phosphine-thioether ligands coordinated to trinuclear Mo3S4 cluster and its effect on hydrogenation catalysis

Phosphine-thioether ligands were coordinated to the Mo₃S₄ cluster to afford [Mo₃S₄Cl₃(PS)₃]⁺ complexes. Their catalytic activity in nitrobenzene reduction reflects the different hemilabile behaviours of PS1, PS2 and PS3.

Synthesis, structure and NMR studies of trinuclear Mo3S4 clusters coordinated with dithiophosphate and chiral carboxylate ligands

Introducing chirality into the Mo₃S₄ cluster has been achieved through coordination of (S)-mandelate and (S)-phenyllactate ligands affording new complexes as a pair of diastereoisomers, (PS) and (MS), represented in the scheme.

Tungsten and molybdenum incomplete cuboidal clusters; kinetico-mechanistic studies and association in dimers

New triangular Mo(IV) and W(IV) incomplete cuboidal cluster complexes containing three η(2)-diethyldithiophosphates (dtp, one per metal centre) and a η(2)(μ)-AcO or η(2)(μ)-dtp ligand bridging two of these centres have been prepared as mono-substituted derivatives and characterized by the usual techniques plus single crystal X-ray diffraction (XRD) analysis in some cases. In the compounds, the single substitutionally available unlocked position is coordinated to different N-donor ligands (1,2-bis(pyridyl)ethylene, pyrimidine, pyrazine) or to the residual solvent. The compounds are very labile and the N-donor ligands are only weakly coordinated, being easily substituted by other donors or coordinating solvents such as acetonitrile. This lability has been explored kinetico-mechanistically by stopped-flow techniques at varying temperatures for the compound [Mo3S4(η(2)-dtp)3(η(2)(μ)-dtp)(H2O)]. By doing so, the nature of the activation process leading to substitution reactions on these complexes has been established as associatively activated and dominated by a very low formation equilibrium constant, that is, by the substitution of the incoming N-donor ligand. Furthermore, the existence of a non-dissociatively activated trigonal 60° fluxional twist has also been established for the η(2)-dtp ligand on the single unlocked position. The lability of the system has also enabled the association in dimers of the acetato derivative, i.e. [Mo3S4(η(2)-dtp)3(η(2)(μ)-AcO)(H2O)], via a pyrazine bridging ligand. After a very careful tuning of the reaction conditions, as established from the kinetico-mechanistic studies, the first single-bridged unsupported dimeric association of {Mo3S4} units, i.e. [{Mo3S4(η(2)-dtp)3(η(2)(μ)-AcO)}2(μ-pyrazine)], has been structurally characterised.