Structural, Spectroscopic, and Computational Analysis of Halogen- and Hydrogen-Bonding Effects within a Series of Uranyl Fluorides with 4-Halopyridinium.

Reported are the syntheses and characterization of five compounds containing one-dimensional uranyl fluoride chains charge balanced by 4-X-pyridinium (X = H, F, Cl, Br, I) cations. Structural analysis reveals molecular assembly via noncovalent interactions in the second coordination sphere with the X···Oyl interaction distances ranging from 2.987(7) to 3.142(3) Å, all of which are less than or close to the sum of the van der Waals radii. These interactions were probed via luminescence and Raman spectroscopy, where the latter indicates slight differences in the U═O symmetric stretches as a consequence of U═O in-phase and out-of-phase Raman-active stretches. The decrease in the X···Oyl sum of the van der Waals overlap between comparable compounds within the series manifests as a red-shifting trend among the Raman symmetric stretches. Computational density functional theory (DFT)-based frequency, electrostatic potential surfaces (ESPs), and natural bonding orbital (NBO) methods support the observed Raman spectroscopic features and provide a comprehensive rationale for assembly.

Orbital Engineering Mediated by Cation Conjugation in Luminescent Uranyl-Organic Hybrid Materials.

A series of compounds of the form [HAr]2 [UO2 X4 ] is reported here, wherein Ar is systematically varied between pyridine (1-X), quinoline (2-X), acridine (3-X), 2,5-dimethylpyrazine (4-X), quinoxaline (5-X), and phenazine (6-X), and X=Cl or Br. With greater conjugation in the organic cation, a larger quenching in uranyl luminescence is observed in the solid state. Supporting our luminescence experiments with computation, we map out the potential energy diagrams for the singlet and triplet states of both the [HAr]+ cations and [UO2 Cl4 ]2- anion in the crystalline state, and of the assembly. The distinct energy transfer pathways in each compound are discussed.

Influence of Metal Identity and Complex Nuclearity in Kumada Cross-Coupling Polymerizations with a Pyridine Diimine-Based Ligand Scaffold.

Cross-coupling polymerizations have fundamentally changed the field of conjugated polymers (CPs) by expanding the scope of accessible materials. Despite the prevalence of cross-coupling in CP synthesis, almost all polymerizations rely on mononuclear Ni or Pd catalysts. Here, we report a systematic exploration of mono- and dinuclear Fe and Ni precatalysts with a pyridine diimine ligand scaffold for Kumada cross-coupling polymerization of a donor thiophene and an acceptor benzotriazole monomers. We observe that variation of the metal identity from Ni to Fe produces contrasting polymerization mechanisms, while complex nuclearity has a minimal impact on reactivity. Specifically, Fe complexes appear to catalyze step-growth Kumada polymerizations and can readily access both Csp2-Csp3 and Csp2-Csp2 cross-couplings, while Ni complexes catalyze chain-growth polymerizations and predominantly Csp2-Csp2 cross-couplings. Thus, our work sheds light on important design parameters for transition metal complexes used in cross-coupling polymerizations, demonstrates the viability of iron catalysis in Kumada polymerization, and opens the door to novel polymer compositions.

Bandgap modification in 0D tellurium iodide perovskite derivatives via incorporation of polyiodide species.

Halide perovskites provide a versatile platform for exploring the effect of non-covalent interactions, including halogen bonding, on material properties such as band gap, luminescence, and frontier orbital landscape. Herein we report six new zero-dimensional tellurium iodide perovskite derivatives, consisting of [TeI6]2- octahedra charge balanced by one of several X-Py cations (X = H, Cl, Br, I, and Py = pyridinium). These compounds also feature robust halogen bonding between [TeI6]2- octahedra and polyiodides in the form of I2 (1-4), I3 - (5), or adjacent octahedra (4 and 6). These relatively strong non-covalent interactions (NCIs) are modeled by natural bond order (NBO) and second order perturbation theory (SOPT) calculations. NCIs are responsible for reducing the bandgap of these materials (measured via diffuse reflectance spectroscopy) relative to those without polyiodide species. They also affect inner sphere bonding in the metal halide, exacerbating [TeI6]2- octahedron asymmetry as compared to previously published compounds, with greater asymmetry correlating with higher van der Waals overlap of halogen-halogen contacts. We also demonstrate the ability of hydrogen and carbon bonding (which dominates in the absence of polyiodides) to affect inner sphere tellurium iodide bonding and octahedral symmetry.

Phenylene as an efficient mediator for intermetallic electronic coupling.

The new compound [(NC)Ru2(ap)4]2(µ-1,4-C6H4) (ap = 2-anilinopyridinate) was prepared to address the open question of whether a 1,4-phenylene bridge can mediate intermetallic electronic coupling. As a manifestation of strong coupling, hole delocalization between the Ru2 centers on the IR time scale (10-14 s) was established using spectroelectrochemistry. An orbital mechanism for coupling was elaborated with DFT analysis.

Macrocyclic Chromium(III) Catecholate Complexes.

The synthesis and structural, electrochemical, spectroscopic, and magnetic characterizations of CrIII(HMC) catecholate and semiquinonate complexes are reported herein, where HMC is 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. cis-[Cr(HMC)(Cat)]+ complexes (Cat = catecholate, [1]+; tetrachlorocatecholate, [2]+; and 3,5-di-tert-butylcatecholate, [3]+) were prepared from the reaction between appropriate catechol and [CrIII(HMC)Cl2]Cl reduced in situ by zinc. Chemical oxidation of [3]+ by FcPF6 resulted in cis-[Cr(HMC)(SQ)]2+ ([3]2+, SQ = 3,5-di-tert-butylsemiquinonate). Single crystal X-ray diffraction studies revealed the cis-chelation of the Cat/SQ ligand around the Cr metal center and confirmed the Cat/SQ nature of the ligands. Reversible oxidations of Cat to SQ were observed in the cyclic voltammograms of [1]+-[3]+, while the CrIII center remains redox inactive. The absorption spectrum of the SQ complex [3]2+ exhibits an intense spin-forbidden transition in solution. Time-delayed phosphorescence spectra recorded at 77 K revealed that all catecholate complexes emit from the 2E state, while [2]+ also emits from the 2T1 state. Temperature-dependent magnetic susceptibility measurements indicate the Cat complexes exist as S = 3/2 systems, while the SQ complex behaves as an S = 1 system, resulting from strong antiferromagnetic coupling of the S = 3/2 Cr center with the S = 1/2 SQ radical. Density functional theory (DFT) shows the similarities between the SOMOs of [1]+ and [2]+ and differences in their LUMOs in the ground state.

Insight into geometric preferences in uranium(VI) mixed tris(imido) systems.

Uranium tris(imido) species have been synthesized using different imido groups in the axial and equatorial positions by treating [(MesPDIMe)U(THF)]2 (1-THF), which is a uranium(iv) dimer that is supported by MesPDIMe tetraanions, with mixed organoazide solutions. While the origin of the geometric preference isn't clear, both steric and electronic factors are likely at play.

Drastic Tuning of the Electronic Structures of Diruthenium Aryl Complexes by Isoelectronic Axial Ligands.

Reported herein is the use of aryls as axial ligands to manipulate reactivity at the distal metal site through metal-metal-ligand interactions in diruthenium paddlewheel complexes. The vacant ruthenium site in Ru2(ap)4(Ar) (1; ap = 2-anilinopyridinate and Ar = C6H4-4-NMe2), thus rendered reactive, is able to bind a series of isoelectronic ligands to afford three complexes of the form (Y)[Ru2(ap)4](Ar) [Y = CN- (2), HC≡C- (3), CO (4)], each of which exhibits a distinct electronic structure. While reactions with anionic ligands subsequently result in oxidation of the diruthenium core from Ru2(II,III) to Ru2(III,III), the reaction with CO yields a rare example of a Ru2(II,III)-COaxial adduct. The latter reaction is particularly interesting in its completely reversible change of the ground state from S = 3/2 in 1 to S = 1/2 in 4, the first of its kind seen in Ru2(II,III) species. In general, this work sheds light on the modulation of the electronic structure of diruthenium paddlewheel complexes using distinct coordination environments around each of the ruthenium centers.

Forging Ru-Csp2 Bonds in Paddlewheel Complexes Using the Lithium-Halogen Exchange Reaction.

Reported herein are the first examples of the formation of Ru-Csp2 bonds in paddlewheel diruthenium species. A series of six Ru2( ap)4(C6H4-4-X) type compounds ( ap = 2-anilinopyridinate; X = NMe2 (1), N,N-(C6H4-4-OMe)2 (2), tBu (3), H (4), Br (5), CF3 (6)) was synthesized by employing the lithium-halogen exchange reaction with a variety of para-substituted aryl halides. These compounds have been characterized via electronic absorption spectroscopy, cyclic voltammetry, mass spectrometry, and magnetism studies, and their molecular structures have been established by single-crystal X-ray diffraction studies. All compounds are in the Ru25+ oxidation state, with a ground-state electronic configuration of σ2π4δ2(π*δ*)3. Crystal structures of 1-6 confirm this, indicating a Ru-Ru bond order of 2.5. Electrochemical data suggest that the σ-aryls are stronger donors than the σ-alkynyls. A range of electronically different substituents allows for a closer inspection of the extent of electronic conjugation across the diruthenium paddlewheel core and the axial aryl ligand.

Heptamolybdate: a highly active sulfide oxygenation catalyst.

The sulfide oxygenation activities of both heptamolybdate ([Mo7O24]6-, [1]6-) and its peroxo adduct [Mo7O22(O2)2]6- ([2]6-) were examined in this contribution. [Mo7O22(O2)2]6- was prepared in a yield of 65% from (NH4)6[Mo7O24] (1a) upon treatment of 10 equiv. of H2O2 and structurally identified through single crystal X-ray diffraction study. (nBu4N)6[Mo7O22(O2)2] (2b) is an efficient catalyst for the sequential oxygenation of methyl phenyl sulfide (MPS) by H2O2 to the corresponding sulfoxide and subsequently sulfone with a 100% utility of H2O2. Surprisingly, (nBu4N)6[Mo7O24] (1b) is a significantly faster catalyst than 2b for MPS oxygenation under identical conditions. The pseudo-first order kcat constants from initial rate kinetics are 54 M-1 s-1 and 19 M-1 s-1 for 1b and 2b, respectively. Electrospray ionization mass spectrometry (ESI-MS) investigation of 1b under the catalytic reaction conditions revealed that [Mo2O11]2- is likely the main active species in sulfide oxygenation by H2O2.