Structural Characterization of a High‐Nuclearity Niobium(V) Carboxylate Cluster Based on Pivalic Acid

Exploring the Structural and Electronic Properties of Niobium Carbide Clusters: A Density Functional Theory Study

This paper systematically investigates the structure, stability, and electronic properties of niobium carbide clusters, NbmCn (m = 5, 6; n = 1-7), using density functional theory. Nb5C2 and Nb5C6 possess higher dissociation energies and second-order difference energies, indicating that they have higher thermodynamic stability. Moreover, ab initio molecular dynamics (AIMD) simulations are used to demonstrate the thermal stability of these structures. The analysis of the density of states indicates that the molecular orbitals of NbmCn (m = 5, 6; n = 1-7) are primarily contributed by niobium atoms, with carbon atoms having a smaller contribution. The composition of the frontier molecular orbitals reveals that niobium atoms contribute approximately 73.1% to 99.8% to NbmCn clusters, while carbon atoms contribute about 0.2% to 26.9%.

Structural Variety of Niobium(V) Polyoxo Clusters Obtained from the Reaction with Aromatic Monocarboxylic Acids: Isolation of {Nb2 O}, {Nb4 O4 } and {Nb8 O12 } Cores

The reactivity of aryl monocarboxylic acids (benzoic, 1- or 2-naphtoic, 4'-methylbiphenyl-4-carboxylic, and anthracene-9-carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)₅ precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb₄ (μ₂ -O)₄ (L)₄ (OEt)₈ ] (L=benzoate (1)) with four Nb-(μ₂ -O)-Nb linkages in a square plane configuration. A similar tetramer, 7, was obtained with 2-naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb-(μ₂ -O)-Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb₂ (μ₂ -O)(μ₂ -OEt)(L)(OEt)₆ ], with L=1-naphtoate (3) or anthracene-9-carboxylate (5)) or two bridging carboxylate groups ([Nb₂ (μ₂ -O)(L)₂ (OEt)₆ ], with L=4'-methylbiphenyl-4-carboxylic (4) or anthracene-9-carboxylate (6)). An octanuclear moiety [Nb₈ (μ₂ -O)₁₂ (L)₈ (η₁ -L)_4-x (OEt)_4+x ] (with L=2-naphtoate, x=0 or 2; 8) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ₂ -O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid ¹ H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb₂ O}, {Nb₄ O₄ } and {Nb₈ O₁₂ } nuclearities.

Molecular niobium(v) complexes with mononuclear {Nb1} and dinuclear oxo species {Nb2O} connected through aryl di- or tetra-carboxylate linker

Di- or tetracarboxylic acid ligands were used to isolate molecular coordination complexes containing the association of several mononuclear {Nb1} moiety and dinuclear {Nb2O} niobium(v) polyoxo clusters.