Binuclear complexes of Ni(i) have been prepared from a 4-terphenyldithiophenol ligand. Steric effects were found to determine the formation of coordination isomeric structures that differ in the nature of metal-to-ligand bonding. Coordination of spatially demanding phosphine ligands PR3, R = C6H6, C6H11, at nickel sites results in a butterfly shaped thiolate-bridged Ni2(μ-S)2 motif. For smaller PMe3, the central π-system of the 4-terphenyl backbone adopts a bis-allyl like μ-syn-η(3):η(3)-C6H4 structure due to significant d-π* Ni(i)-to-ligand charge transfer. Delocalisation indices δ(Ni-Ni) derived from DFT calculations provide a metric to assess the strength of electronic coupling of the Ni sites based on solid state structural data, and indicated less strong electronic coupling for the bis-allyl like structure with δ(Ni-Ni) = 0.225 as compared to 0.548 for the Ni2(μ-S)2 structural motif. A qualitative reactivity study toward CNCH3 as an auxiliary ligand has provided the first insight into the chemical properties of the bimetallic complexes presented.
The magnetic properties of FexO with long-range order of defects was studied. The crystal structure appears to consist of periodically spaced complexes of vacant octahedral and occupied tetrahedral sites, with most of the octahedral ions in an ideal NaCl-type environment. The Néel temperature, determined from measurements of susceptibility and modulus, increases very slightly as x is decreased. Octahedral-tetrahedral ion exchange interactions are proposed to account for the increase in TN. The molar susceptibility obeys a Curie-Weiss law, χ = 3.56/(T+136). With θ = 136°K and TN about 200°K, θ/TN is less than one. According to a treatment by Van Vleck one expects θ/TN greater than one for negative first-near-neighbor and second-near-neighbor interactions. A positive first-near-neighbor interaction may possibly arise through double exchange between Fe2+ and Fe3+.
This work reports on the redox and acid–base properties of binuclear complexes of nickel from 1,4‐terphenyldithiophenol ligands. The results provide insight into the cooperative electronic interaction between a dinickel core and its ligand. Donor/acceptor contributions flexibly adjust to stabilize different redox states at the metals, which is relevant for redox reactions like proton reduction. Proton transfer to the [S2Ni2] core and Ni−H bond formation are kinetically favored over the thermodynamically favored yet unproductive proton transfer to ligand.
Sulfur-bridged binuclear structures [2M-2S] play a pivotal role in a variety of chemical processes such as bond breaking and formation and electron transfer. In general, structural persistence is deemed essential to the respective function but owing to the lack of a suitable molecular model system, the current understanding of the factors that control the thermodynamic and kinetic stability of [2M-2S] cores clearly is limited. This work reports a series of binuclear complexes of nickel derived from a 1,4-terphenyldithiophenol ligand platform that is ideally suited for mechanistic work to overcome this limitation. Redox-induced assembly and disassembly of S-bridged [2M-2S] fragments have been investigated at the molecular level. As part of an extended square scheme, metastable binuclear structures that are significant mechanistically have been identified, characterized, and their reactivity studied quantitatively. Electronic properties that are inherent to [2M-2S] structures and determine thermodynamic and kinetic stability are differentiated from steric effects imposed by co-ligands.
The chemical bond between a Lewis-acidic metal and a Brønsted/Lewis-basic sulphur donor provides M-S structures with functional properties that are relevant for a variety of processes such as the heterolytic cleavage of H. Direct comparison of reactivity properties between molecular M-S structures can be difficult owing to divergent electronic properties of stabilizing ligand scaffolds. This work reports on a mechanistic study of stoichiometric H oxidation at electronically distinct [Ni(μ-SR)] and [Ni-SR] structures that derive from the same 1,4-terphenyldithiophenol ligand. In this context, the effect of metal containing side-products such as [HNi(PMe)] on overall H oxidation reactivity displayed by Ni-S structures has been investigated quantitatively in addition to external parameters such as solvent and H pressure.
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