Symmetrical disubstituted carbohydrazides (H₄L^1–6) when reacted with [MoO₂(acac)₂] (in 1 : 2 molar ratio) afford the corresponding discrete complexes, [(MoO₂)₂L^1,5,6(MeOH)₂], [(MoO₂)₂L^1,5,6(Im)₂] (Im = imidazole), and/or polymeric ensembles, [(MoO₂)₂L^1–6]_n, depending on the reaction solvent, the ligand framework and the presence of ancillary coordinating species. In these assemblies, asymmetrical dimolybdenum(VI) entities, [(MoO₂)₂L^1–6], wherein the corresponding carbohydrazide acts as an adaptable two-compartment ligand offering ONO and ONN coordination environments, serve as the main building blocks. The solid-state structures of the obtained materials were elucidated via X-ray diffraction and infrared spectroscopy, whereas the behaviour of polymeric ensembles in DMSO-d₆ solution was investigated by nuclear magnetic resonance. Thermal studies revealed that the discrete species transform to the corresponding polymeric ensembles upon heating, whereas upon grinding they either remain intact or afford their reactive and coordinatively unsaturated (pentacoordinated) counterparts. While the discrete methanol-based complexes have a comparable spatial arrangement of ancillary ligands, imidazole-based ones offer substantially different scenario which was addressed in detail via density functional theory calculations. Finally, the polymeric ensembles were shown to be efficient catalysts for cyclooctene epoxidation under eco-friendly conditions while employing aqueous tert-butyl hydroperoxide as an oxidant.

In this study, we examine the experimental and theoretical capabilities of two perhalogenated anilines, 2,3,5,6-tetrafluoro-4-bromoaniline (btfa) and 2,3,5,6-tetrafluoro-4-iodoaniline (itfa) as hydrogen and halogen bond donors. A series of 11 cocrystals derived from the two anilines and selected ditopic nitrogen-containing acceptors (4,4'-bipyridine, 1,2-bis(4-pyridyl)ethane, and 1,4-diazabicyclo[2.2.2]octane) in 1:1 and 2:1 stoichiometries were prepared by liquid-assisted grinding and crystallization from solution. Crystallographic analysis revealed bifunctional donor properties in both anilines. The dominant supramolecular interaction in four cocrystals of btfa is the N-H···N_acceptor hydrogen bond between btfa and acceptor molecules, while in the one remaining cocrystal, donor and acceptor molecules are connected via the N-H···N_acceptor hydrogen bond and the Br···N_acceptor halogen bond. In two cocrystals of itfa, the dominant supramolecular interaction is the I···N_acceptor halogen bond between itfa and acceptor molecules, while in the remaining four cocrystals, donor and acceptor molecules are additionally connected by the N-H···N_acceptor hydrogen bond. Periodic density-functional theory (DFT) calculations have been conducted to assess the formation energies of these cocrystals and the strengths of the established halogen and hydrogen bonds. Molecular DFT calculations on btfa and itfa indicate that the differences in electrostatic potential between the competing sites on the molecules are 261.6 and 157.0 kJ mol^-1 e^-1, respectively. The findings suggest that itfa, with a smaller electrostatic potential difference between donor sites, is more predisposed to act as a bifunctional donor.

Coordination-driven self-assembly approach offers opportunity for designing metallosupramolecular architectures with tailored properties. Applying this strategy, we present the synthesis and detailed characterization of tetranuclear and polynuclear vanadium(V) compounds with an aroylhydrazone ligand. These assemblies were obtained using the 3-methoxy-2-hydroxybenzaldehyde isonicotinoyl hydrazone ligand (H₂VIH) and NH₄VO₃ in the presence of primary alcohols of increasing carbon chain length (from one to five carbon atoms). Reactions in lower alcohols selectively yielded metallocyclic compounds [VO(VIH)(OR)]₄ (1, 2, and 3, where R = CH₃, C₂H₅, and C₃H₇, respectively), while reactions in higher alcohols afforded infinite zig-zag chain polymers [VO(VIH)(OR)]_n (4 and 5, where R = C₄H₉ and C₅H₁₁, respectively). Their formation was studied experimentally and computationally. Quantum chemical calculations using density functional theory provided valuable insights into the stability of both cyclic and chain assemblies. The solid-state structures of 1–5 and pseudopolymorphs of [VO₂(HVIH)] (6·0.5H₂O·0.5CH₃OH and 6·2H₂O) were confirmed using single-crystal and powder X-ray diffraction methods. The oxovanadium(V) species were tested as catalysts for cyclooctene and benzyl alcohol oxidation, with results correlated to those for analogous molybdenum complexes [MoO₂(VIH)]₄ (7) and [MoO₂(VIH)(C₂H₅OH)] (8). The influence of the metal centre, nuclearity, and ancillary ligand identity on catalytic performance was also investigated, revealing that the vanadium metal center influences the catalytic activity due to its capacity to form robust structures.

In this work, we explore the halogen-bonded cocrystallization potential of cobaloxime complexes in the synthesis of cocrystals with perhalogenated benzenes. We demonstrate a strategy for synthesizing halogen-bonded metal–organic cocrystals by utilizing cobaloximes whose pendant bromide group and oxime oxygen enable halogen bonding. By combining three well-known halogen bond donor molecules differing in binding geometry and composition with three cobaloxime units, we obtained a total of four previously unreported cocrystals. Single crystal X-ray diffraction experiments showed that the majority of obtained cocrystals exhibited the formation of the targeted I···O and I···Br motives. These results illustrate the potential of cobaloximes as halogen bond acceptors and indicate that this type of halogen bond acceptors may offer a novel route to metal–organic halogen-bonded cocrystals.