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Triple pnictogen bonding refers to the ability of a pnictogen atom to engage in three simultaneous pnictogen bonds (PnBs) to a complementary partner through a single pnictogen atom. This supramolecular strategy was recently introduced as a unique facet of pnictogen bonding as compared to other named supramolecular interactions. Here, the ability of bismuth to participate in this phenomenon is demonstrated using Bi((NC9H7)3CH3). The study reveals that Bi engages in stronger PnBs than the analogous Sb system. The results have been contrasted with Bi systems that form strong coordination bonds, and analysis of the electron density along the bond path reveals key differences. The solution behavior of these newly synthesized supramolecules were studied by PFGSE NMR spectroscopy and they are found to remain intact in solution. Molecular design strategies that allow for triple pnictogen bonding should find use in the fields of molecular recognition and crystal engineering.

The structure of the simplest stibatrane has been a mystery since it was first prepared in 1966. This study reports the preparation and characterization of two stibatranes from triethanolamine and triisopropanolamine. Solid state structures reveal macrocycles that contain favourable inter- and intramolecular pnictogen bonds. Solution studies, corroborated by DFT analysis, reveal an equilibrium mixture assigned to monomer and pnictogen-bonded dimer. This allowed for the determination of an enthalpy associated with pnictogen bond formation of -27 kJ mol

The diverse optical, magnetic, and electronic behaviors of most colloidal semiconductor nanocrystals emerge from materials with limited structural and elemental compositions. Conductive metal-organic frameworks (MOFs) possess rich compositions with complex architectures but remain unexplored as nanocrystals, hindering their incorporation into scalable devices. Here, we report the controllable synthesis of conductive MOF nanoparticles based on Fe(1,2,3-triazolate)

In the development of crystal engineering and supramolecular chemistry, cocrystallization has been used as a way to develop novel explosives with tailored properties. We present a novel cocrystal s...

Supramolecular assembly utilizing simultaneous formation of three pnictogen bonds around a single antimony vertex was explored via X-ray crystallography, solution NMR, and computational chemistry. An arylethynyl (AE) ligand was designed to complement the three electrophilic regions around the Sb compound. Though solution studies reveal large binding constants for individual pyridyl units with the Sb donor, the rigidity and prearrangement of the AE acceptor proved necessary to achieve simultaneous binding of three acceptors to the Sb-centered pnictogen-bond donor. Calculations and X-ray structures suggest that negative cooperativity upon sequential binding of three acceptors to a Sb center limits the utility of triple-pnictogen bonding pyridyl acceptors. These limitations can be negated, however, when positive cooperativity is designed into a complementary acceptor ligand.

Reduction of the tetrahedral complex (BIAN)FeCl2 (6) (BIAN = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) in the presence of an arene, either as reaction solvent or in pentane solution affords a series of (BIAN)Fe(η6-arene) complexes (10–13). In the case of the sterically encumbered arene 2-methylnapthalene, 6 was converted to the (BIAN)Fe(COD) (14) (COD = 1,5-cyclooctadiene) complex first, before subsequent hydrogenation in the presence of 2-methylnaphthalene afforded the desired arene complex (15). The electronic structure of the arene complexes was interrogated, and the question of ligand redox non-innocence was addressed using X-ray diffraction studies as well as DFT and cyclic voltammetry.

Iodine functionalized variants of DUT-5 (Al) and UiO-67 (Zr) were prepared as expanded-pore analogues of MIL-53 (Al) and UiO-67 (Zr). They were prepared using a combination of multivariate and isorecticular expansion strategies. Multivariate MOFs with a 25% iodine-containing linker was chosen to achieve an ideal balance between a high density of catalytic sites and sufficient space for efficient diffusion. Changes to the oxidation potential of the catalyst as a result of the pore-expansion strategy led to a decrease in activity with electron rich substrates. On the other hand, these larger frameworks proved to be more efficient catalysts for substrates with higher oxidation potentials. Recyclability tests for these larger MOFs showed sustained catalytic activity over multiple recycles.

Pnictogen bonding is beginning to emerge as a useful supramolecular interaction. The design strategies for these systems are still in the early stages of development and much attention has been focused on the lighter pnictogens. Pnictogen bond donors can have up to three independent sites for binding which can result in triple pnictogen bonding. This has been observed in the self-assembly of antimony alkoxide cages, but not with the lighter congeners. This work reports structural characterization of an analogous arsenic alkoxide cage that engages in a single pnictogen bond and synthetic explorations of the bismuth congener. DFT calculations are used to evaluate the differences between the structures. Ultimately the partial charge on the pnictogen and the energy of the pnictogen lone pair dictate the strength, orientation and number of pnictogen bonds that these cages form. Antimony cages strike the best balance between strength and directionality, allowing them to achieve triple pnictogen bonding where the other congeners do not.

A new air and moisture stable antimony thiolate compound has been prepared that spontaneously forms stable hollow vesicles., A new air and moisture stable antimony thiolate compound has been prepared that spontaneously forms stable hollow vesicles. Structural data reveals that pnictogen bonding drives the self-assembly of these molecules into a reversed bilayer. The ability to make these hollow, spherical, and chemically and temporally stable vesicles that can be broken and reformed by sonication allows these systems to be used for encapsulation and compartmentalisation in organic media. This was demonstrated through the encapsulation and characterization of several small organic reporter molecules.

Pharmaceuticals have been found as contaminants in wastewater, causing concern for the health of aquatic life and humans. The anti-cholesterol medication bezafibrate is one such contaminant and is difficult to remove from wastewater. The lack of studies investigating the bonding behavior of bezafibrate with potential acceptor motifs prompted us to determine the types of molecules that would engage in intermolecular bonds with the drug. Although co-crystallization of bezafibrate has been previously attempted, we altered the approach by utilizing molecules containing only hydrogen-bond-acceptor sites. Here, we discuss the first successful co-crystallizations of bezafibrate, intermolecular bonding behavior, and solution-state binding studies with potential acceptor molecules. One acceptor, 4-dimethylaminopyridine, exhibits a shorter bond in the solid state, and a solution-state binding constant over 18 times higher than any other drug–acceptor pair studied here. These studies should aid in designing contamin...

Catalytic Meerwein-Ponndorf-Verley reductions of ketones and aldehydes in the presence of isopropyl alcohol were performed at aluminum alkoxide sites that were postsynthetically introduced into robust metal-organic frameworks (MOFs). The aluminum was anchored at the bridging hydroxyl sites inherent in some MOFs. MOFs in the UiO-66/67 family as well as DUT-5 were successfully adapted to this strategy. Incorporation of catalytically active aluminum species greatly enhanced the reactivity of the native MOF at 80 °C in the case of both UiO-66, and was almost solely responsible for catalytic activity in the case of metalated UiO-66 and DUT-5. The site isolation of the catalyst prevented aggregation and complete deactivation of the molecular aluminum catalyst, allowing it to be recovered and recycled in the case of UiO-67. This catalyst also proved to be moderately tolerant to wet isopropyl alcohol.

The solution and gas phase halide binding to a bis-antimony(iii) anion receptor was studied. This new class of anion receptors utilizes the strong Sb-centered secondary bonding interactions (SBIs) that are formed opposite to the polar Sb-O primary bond. 1H NMR titration data were fitted statistically to binding models and solution-phase binding energetics were extracted, while the formation of anion-to-receptor complexes was observed using ESI-MS. Density functional theory calculations suggest that their affinity towards binding halide anions is mitigated by the strong explicit solvation effect in DMSO, which gives insights into future designs that circumvent direct solvent binding and are anticipated to yield tighter and perhaps more selectivity in anion binding.

Iodine sites have been incorporated in both MIL-53 (Al) and UiO-66 (Zr) MOFs. A multivariate approach was used to increase the accessible area within the pores to allow for the catalytic oxidation of a model substrate, hydroquinone, to the corresponding quinone. In the process, three new phases of MIL-53 were discovered, one of which proved instrumental in allowing catalysis to occur. Both UiO-66 and MIL-53 with 25% incorporated iodine containing linkers allowed for a near-ideal balance between high density of catalytic sites and sufficient space for mass transport to enable catalysis to occur. Good conversions and selectivities were observed in nitromethane, ethyl acetate, acetone and ethanol with UiO-66 which proved to be the more active of the two catalysts. Oxone and 3-chloroperbenzoic acid acted as competent co-oxidants. X-ray photoelectron spectroscopy revealed that the reaction proceeded through an I(III) oxidation state. The MIL-53 framework was readily recycled while the UiO-66 MOF suffered from catalyst deactivation due to particle agglomeration. UiO-66 with 25% iodine containing linker proved to be a competent catalyst for a variety of substituted hydroquinones.

Antimony(III) alkoxide cages were designed as building blocks for predictable supramolecular self-assembly. Supramolecular synthons featuring two Sb···O secondary bonding interactions (SBIs), each SBI stronger than 30 kJ/mol, were used to drive the formation of the supramolecular architectures. Judicious choice of pendant groups provided predictable control over the formation of self-assembled 3D columnar helices, which crystallized with hollow morphologies, or a self-assembled 2D bilayer. The Sb-O stretching frequency provides a spectroscopic signature of Sb···O SBI formation.

The reaction of (dppBIAN)FeCl2 with 3 equivalents of n-BuLi affords a catalytically active anionic Fe complex; the nature of the anionic complex was probed using EPR and IR experiments and is proposed to involve a dearomatized, radical, ligand scaffold. This complex is an active catalyst for the hydrosilylation of esters to afford alcohols; loadings as low as 1 mol% were employed.

Artificial vesicles can aid in the study and understanding of biological cell membranes. This study employs pnictogen bonding to actively direct the self-assembly of a true reversed bilayer. Antimony(III) alkoxide cages that self-assemble through multiple strong Sb⋯O interactions propagate in two dimensions to form a reverse bilayer structure in the solid state. Long alkyl tails allow these reverse bilayers to be processed into vesicles in solution that are a reverse of biological cell membranes.

Alkaloids compose a large class of natural products, and mono-methylated polyamines are a common intermediate in their biosynthesis. In order to evaluate the role of selectively methylated natural products, synthetic strategies are needed to prepare them. Here, N-methylcadaverine is prepared in 37.3% yield in three steps. The alternative literature two-step strategy resulted in reductive deamination to give N-methylpiperidine as determined by the single crystal structure. A straightforward strategy to obtain the mono-alkylated aliphatic diamine, cadaverine, which avoids potential side-reactions, is demonstrated.

Carboxamidines functionalized with either a spiropyran or fulgimide photoswitch were prepared on multigram scales. The thermal, electrochemical, and photochemical ring isomerizations of these compounds were studied and the results compared with related systems. The photochemical isomerisations were found to be reversible and could be followed by 1H NMR and UV-vis spectroscopy. The spiropyran/merocyanine couple was thermally active and an activation enthalpy of 116 kJ mol−1 was measured for ring-opening. These measurements yielded an enthalpy difference of 25 kJ mol−1 between the open and closed states which is consistent with DFT calculations. DFT calculations predicted a charge transfer to the carboxamidine group upon ring closure in the fulgimide and a charge transfer from the carboxamidine group upon switching the spiropyran to the merocyanine form. This was confirmed experimentally by monitoring the change in the oxidation potential assigned to the carboxamidine group. The potential of these molecules to therefore act as a new class of photoresponsive ligands that can modulate the ligand field of a complex is discussed.

Financial support from the National Science Foundation (MFM research grant CHE-0847736 and NMR instrument grant CHE-1048553) and the Robert A. Welch Foundation (AFC grant D-1838 and MF grant D-1807) are gratefully acknowledged. The synthesis, characterization, photophysical properties, theoretical calculations, and catalytic studies of 2,9-di(aryl)-1,10-phenanthroline copper (I) complexes are described. Specifically, this study made use of di(aryl)-1,10-phenanthroline ligands including 2,9-di(4-methoxyphenyl)-1,10-phenanthroline ( 1 ), 2,9-di(4-hydroxyphenyl)-1,10-phenanthroline ( 2 ), 2,9-di(4-methoxy-3-methylphenyl)-1,10-phenanthroline ( 3 ), and 2,9-di(4-hydroxy-3-methylphenyl)-1,10-phenanthroline ( 4 ). The 2:1 ligand-to-metal complexes, as PF6- salts, i.e., ([Cu·( 1 )2]PF6, [Cu·( 2 )2]PF6, [Cu·( 3 )2]PF6, and [Cu·( 4 )2]PF6) have been isolated and characterized. The structures of ligands 1 and 2 and complexes [Cu·( 1 )2]PF6 and [Cu·( 3 )2]PF6 have been determined by single-crystal X-ray analysis. The photoredox catalytic activity of these copper(I) complexes was investigated in an atom-transfer radical-addition (ATRA) reaction and the results showed fairly efficient activity, with a strong wavelength dependence. In order to better understand the observed catalytic activity, photophysical emission and absorption studies, and DFT calculations were also performed. It was determined that when the excitation wavelength was appropriate for exciting into the LUMO+1 or LUMO+2, catalysis would occur. On the contrary, excitations into the LUMO resulted in no observable catalysis. In light of these results, a mechanism for the ATRA photoredox catalytic cycle has been proposed. Postprint

Unsaturated metal sites within the nodes of metal-organic frameworks (MOFs) can be interrogated by redox reagents common to small molecule chemistry. We show, for the first time, that an analogue of the iconic M2(2,5-dioxidoterephthalate) (M2DOBDC, MOF-74) class of materials can be stoichiometrically oxidized by one electron per metal center. The reaction of Mn2DOBDC with C6H5ICl2 produces the oxidized material Cl2Mn2DOBDC, which retains crystallinity and porosity. Surprisingly, magnetic measurements, X-ray absorption, and infrared spectroscopic data indicate that the Mn ions maintain a formal oxidation state of +2, suggesting instead the oxidation of the DOBDC(4-) ligand to the quinone DOBDC(2-). These results describe the first example of ligand redox non-innocence in a MOF and a rare instance of stoichiometric electron transfer involving the metal nodes. The methods described herein offer a synthetic toolkit that will be of general use for further explorations of the redox reactivity of MOF nodes.

We employed multiwavelength anomalous X-ray dispersion to determine the relative cation occupation at two crystallographically distinct metal sites in Fe2+-, Cu2+-, and Zn2+-exchanged versions of the microporous metal–organic framework (MOF) known as MnMnBTT (BTT = 1,3,5-benzenetristetrazolate). By exploiting the dispersive differences between Mn, Fe, Cu, and Zn, the extent and location of cation exchange were determined from single crystal X-ray diffraction data sets collected near the K edges of Mn2+ and of the substituting metal, and at a wavelength remote from either edge as a reference. Comparing the anomalous dispersion between these measurements indicated that the extent of Mn2+ replacement depends on the identity of the substituting metal. We contrasted two unique methods to analyze this data with a conventional approach and evaluated their limitations with emphasis on the general application of this method to other heterometallic MOFs, where site-specific metal identification is fundamental to tu...

The mass spectra of benzo-2,1,3-chalcogenadiazoles, acquired from the equilibrium conditions of the UV-laser desorption/ionization plume, contain isotopic patterns that are characteristic of protonated and ionized dimers. Dispersion-corrected DFT modeling shows that the most stable structures of these dimers feature the supramolecular four-membered Te2N2 ring, which is pervasive in the crystal structures of these compounds. These observations provide the first evidence of the persistence of Te–N supramolecular association in the gas phase.

Density functional theory calculations were used to design an anion receptor that utilizes antimony(III) secondary bonding interactions. Calculations were performed on promising motifs found in the chemical literature where two antimony sites were found in close proximity to a halide anion. The study was extended to a structurally related class of 1,3,2-benzodioxastibole derivatives to elucidate their potential for binding halide ions. Multiple geometric conformations were evaluated and various ratios of halide anions were considered. According to the computation results, this class of anion receptors shows strong affinities toward charge-dense halides. These 1,3,2-benzodioxastibole derivatives were prepared to evaluate their synthetic accessibility. Structural characterization of one species revealed the ability to bind up to three electron donors through secondary bonding interactions. This gates the future experimental study of these antimony systems for anion binding and recognition.

Treatment of V(N[(t)Bu]Ar)(3) (1) (Ar = 3,5-Me(2)C(6)H(3)) with O(2) was shown by stopped-flow kinetic studies to result in the rapid formation of (η(1)-O(2))V(N[(t)Bu]Ar)(3) (2) (ΔH(‡) = 3.3 ± 0.2 kcal/mol and ΔS(‡) = -22 ± 1 cal mol(-1) K(-1)), which subsequently isomerizes to (η(2)-O(2))V(N[(t)Bu]Ar)(3) (3) (ΔH(‡) = 10.3 ± 0.9 kcal/mol and ΔS(‡) = -6 ± 4 cal mol(-1) K(-1)). The enthalpy of binding of O(2) to form 3 is -75.0 ± 2.0 kcal/mol, as measured by solution calorimetry. The reaction of 3 and 1 to form 2 equiv of O≡V(N[(t)Bu]Ar)(3) (4) occurs by initial isomerization of 3 to 2. The results of computational studies of this rearrangement (ΔH = 4.2 kcal/mol; ΔH(‡) = 16 kcal/mol) are in accord with experimental data (ΔH = 4 ± 3 kcal/mol; ΔH(‡) = 14 ± 3 kcal/mol). With the aim of suppressing the formation of 4, the reaction of O(2) with 1 in the presence of (t)BuCN was studied. At -45 °C, the principal products of this reaction are 3 and (t)BuC(═O)N≡V(N[(t)Bu]Ar)(3) (5), in which the bound nitrile has been oxidized. Crystal structures of 3 and 5 are reported.

Treatment of N,N-dialkyl-4-[4-nitrophenyl)diazenyl] anilines with a mercury(II) salt in anhydrous trifluoroacetic acid results in single and double metallation of the ring with less electron density. The seemingly counterintuitive outcome of the reaction was rationalized through experimental and computational investigations of the reaction mechanism.

Molecules that exhibit emission in the solid state, especially those known as aggregation-induced emission (AIE) chromophores, have found applications in areas as varied as light-emitting diodes and biological sensors. Despite numerous studies, the mechanism of fluorescence quenching in AIE chromophores is still not completely understood. To this end, much interest has focused on understanding the low-frequency vibrational dynamics of prototypical systems, such as tetraphenylethylene (TPE), in the hope that such studies would provide more general principles toward the design of new sensors and electronic materials. We hereby show that a perdeuterated TPE-based metal-organic framework (MOF) serves as an excellent platform for studying the low-energy vibrational modes of AIE-type chromophores. In particular, we use solid-state (2)H and (13)C NMR experiments to investigate the phenyl ring dynamics of TPE cores that are coordinatively trapped inside a MOF and find a phenyl ring flipping energy barrier of 43(6) kJ/mol. DFT calculations are then used to deconvolute the electronic and steric contributions to this flipping barrier. Finally, we couple the NMR and DFT studies with variable-temperature X-ray diffraction experiments to propose that both the ethylenic C═C bond twist and the torsion of the phenyl rings are important for quenching emission in TPE, but that the former may gate the latter. To conclude, we use these findings to propose a set of design criteria for the development of tunable turn-on porous sensors constructed from AIE-type molecules, particularly as applied to the design of new multifunctional MOFs.

The crystal structures of tellurium compounds frequently display intermolecular contacts between the chalcogen and atoms possessing lone pairs of electrons. Analysis of the data deposited in the Cambridge crystallographic database shows that the shortest secondary bonding interactions (SBIs) are formed when oxygen, nitrogen or chlorine are the donor atoms for SBIs. In addition, these SBIs are shortest when they occur opposite to a bond between tellurium and oxygen, nitrogen, fluorine, chlorine or the nitrile functional group. The structural motifs assembled in these systems fall within eight general categories, from single to multiple bonded supramolecular synthons. The use of multiple points of attachment between molecules leads, in principle, to stronger and more directional supramolecular synthons. The overall structures assembled by the most important tellurium-based supramolecular synthons and prospects for their application in crystal engineering are discussed.

1,2,5-Telluradiazole rings have a remarkably strong tendency toward association through Te-N secondary bonding interactions in the solid state. The reproducibility of the bond lengths and angles in the known crystal structures allowed the parametrization of an anharmonic force field to accommodate both the inter- and intramolecular Te-N bonds. The new parameters were tested against published crystal structures and were able to accurately reproduce the experimentally observed geometries. The incorporation of these parameters into a molecular mechanics force field enables the modeling of large and complex structures with significantly less computational effort than Hartree—Fock (HF) or density functional theory (DFT) methods. Simple modifications to the parameter set allowed the modeling of the structures of acyclic tellurium diamides. A series of 4,7-disubstituted benzo-2,1,3-telluradiazoles were modeled to probe the steric barrier of dimerization; only the groups with large spherical bulks such as t-butyl, trimethylsilyl, and adamantyl were able to destabilize the dimers. Modeling based on bifunctional building blocks suggests strategies for the construction of novel two- and three-dimensional supramolecular architectures.

Moderate steric repulsion within the supramolecular ribbon chains assembled by 1,2,5-telluradiazole derivatives causes a distortion of the [Te−N]2 supramolecular synthon which removes the inversion center from the four-membered virtual ring. This geometrical feature can propagate through the lattice, creating a noncentrosymmetric crystal with second-order nonlinear optical (NLO) properties. This principle was demonstrated in the cases of 3,4-dicyano-1,2,5-telluradiazole and 5,6-dichlorobenzo-2,1,3-telluradiazole. The second harmonic generation efficiency of these materials, however, is modest because the molecular dipole moments have a nearly antiparallel arrangement in the ribbons. The structure of 5-benzoylbenzo-2,1,3-telluradiazole demonstrates that it is indeed possible to extend this strategy to generate acentric crystals of benzo-2,1,3-telluradiazoles featuring pendant groups (including NLO chromophores) and in this way design more efficient NLO materials.

The cyclocondensation of acetylferrocene and acetylcymantrene catalyzed by SiCl4 in ethanol yields a mixture of 1,3,5-trisubstituted benzenes and the intermediate 3,1-disubstituted (E)-2-buten-1-ones, including all the homo- and heterometallic species, which were separated and quantified by HPLC. The relative yields of these species are determined by the different ability of the organometallic groups to stabilize the cationic intermediates that participate in the reaction mechanism, which is measurable as the basicity of the starting materials. The X-ray crystal structures of 1-cymantrenyl-3,5-diferrocenylbenzene and (E)-3-cymantrenyl-1-ferrocenyl-2-buten-1-one are described within this report.

1,2,5-Chalcogenadiazoles, in particular the tellurium derivatives, are promising building blocks for the assembly supramolecular structures through the formation of the [E–N] 2 (E = S, Se, Te) supramolecular synthon. This short account summarizes initial experimental and computational investigations in this area.

DFT calculations were used to compare the magnitude of steric repulsion to the strength of secondary bonding interactions (SBIs) in the (Te−N)2 supramolecular synthon to explain or predict the supramolecular structures assembled by two derivatives of the 1,2,5-telluradiazole ring: benzo-2,1,3-telluradiazole (4c) and 3,6-dibromobenzo-2,1,3-telluradiazole (5). The crystallographically determined structures were consistent with the computational predictions. In sharp contrast with the previously known structures of its sulfur and selenium analogues, 4c forms infinite ribbon chains in the solid state with 2.682(7)−2.720(7) A Te−N SBIs. Steric hindrance in 5 restricted the supramolecular association to form discrete dimers with 2.697(8) A Te−N SBIs. In addition to discrete dimers, the dibromo derivative crystallizes as solvated dimers in 5·DMSO with 2.834(5) A Te−O SBIs. Other weaker SBIs were identified in the crystal lattices and were assessed by the computational method.

Organochalcogen-nitrogen heterocycles such as the 1,2,5-chalcogenadiazoles have a distinct tendency to establish intermolecular links in the solid state through secondary bonding interactions E...N (E = S, Se, Te). The association of these molecules was examined in detail using relativistic density functional theory. Although there is an important electrostatic component, the interaction between these molecules is dominated by contributions arising from orbital mixing, which can be interpreted as the donation of a nitrogen lone pair into the chalcogen-centered antibonding orbitals. Because of its more polar character and lower-lying antibonding orbitals, the tellurium derivatives possess the strongest association energies; these are so large that the binding strength is comparable to that of some hydrogen bonds. In the absence of steric constraints, telluradiazoles associate in a coplanar fashion forming ribbon polymers. However, bulky susbstituents could be used to direct the formation of either helical chains or discrete dimers. In addition to its strength, the coplanar dimer is characterized by being rigid, yet no activation barrier is expected for the association/dissociation process. These attributes strongly indicate that tellurium-nitrogen heterocycles have great potential as building blocks in supramolecular architecture.

An important challenge in the artificial fixation of N[subscript 2] is to find atom efficient transformations that yield value-added products. Here we explore the coordination complex mediated conversion of ubiquitous species, CO and N[subscript 2], into isocyanate. We have conceptually split the process into three steps: (1) the six-electron splitting of dinitrogen into terminal metal nitrido ligands, (2) the reduction of the complex by two electrons with CO to form an isocyanate linkage, and (3) the one electron reduction of the metal isocyanate complex to regenerate the starting metal complex and release the product. These steps are explored separately in an attempt to understand the limitations of each step and what is required of a coordination complex in order to facilitate a catalytic cycle. The possibility of this cyanate cycle was explored with both Mo and V complexes which have previously been shown to perform select steps in the sequence. Experimental results demonstrate the feasibility of some of the steps and DFT calculations suggest that, although the reduction of the terminal metal nitride complex by carbon monoxide should be thermodynamically favorable, there is a large kinetic barrier associated with the change in spin state which can be avoided in the case of the V complexes by an initial binding of the CO to the metal center followed by rearrangement. This mandates certain minimal design principles for the metal complex: the metal center should be sterically accessible for CO binding and the ligands should not readily succumb to CO insertion reactions., National Science Foundation (U.S.) (CHE-1111357)

We show that fluorescent molecules incorporated as ligands in rigid, porous metal-organic frameworks (MOFs) maintain their fluorescence response to a much higher temperature than in molecular crystals. The remarkable high-temperature ligand-based fluorescence, demonstrated here with tetraphenylethylene- and dihydroxyterephthalate-based linkers, is essential for enabling selective and rapid detection of analytes in the gas phase. Both Zn2(TCPE) (TCPE = tetrakis(4-carboxyphenyl)ethylene) and Mg(H2DHBDC) (H2DHBDC(2-) = 2,5-dihydroxybenzene-1,4-dicarboxylate) function as selective sensors for ammonia at 100 °C, although neither shows NH3 selectivity at room temperature. Variable-temperature diffuse-reflectance infrared spectroscopy, fluorescence spectroscopy, and X-ray crystallography are coupled with density-functional calculations to interrogate the temperature-dependent guest-framework interactions and the preferential analyte binding in each material. These results describe a heretofore unrecognized, yet potentially general property of many rigid, fluorescent MOFs and portend new applications for these materials in selective sensors, with selectivity profiles that can be tuned as a function of temperature.

Thermodynamic, kinetic, and computational studies are reported for oxygen atom transfer (OAT) to the complex V(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2, 1) from compounds containing N-O bonds with a range of BDEs spanning nearly 100 kcal mol(-1): PhNO (108)SIPr/MesCNO (75)PyO (63)IPr/N2O (62)MesCNO (53)N2O (40)dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene; Py = pyridine; IPr = 1,3-bis(diisopropyl)phenylimidazol-2-ylidene; dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene). Stopped flow kinetic studies of the OAT reactions show a range of kinetic behavior influenced by both the mode and strength of coordination of the O donor and its ease of atom transfer. Four categories of kinetic behavior are observed depending upon the magnitudes of the rate constants involved: (I) dinuclear OAT following an overall third order rate law (N2O); (II) formation of stable oxidant-bound complexes followed by OAT in a separate step (PyO and PhNO); (III) transient formation and decay of metastable oxidant-bound intermediates on the same time scale as OAT (SIPr/MesCNO and IPr/N2O); (IV) steady-state kinetics in which no detectable intermediates are observed (dbabhNO and MesCNO). Thermochemical studies of OAT to 1 show that the V-O bond in O≡V(N[t-Bu]Ar)3 is strong (BDE = 154 ± 3 kcal mol(-1)) compared with all the N-O bonds cleaved. In contrast, measurement of the N-O bond in dbabhNO show it to be especially weak (BDE = 10 ± 3 kcal mol(-1)) and that dissociation of dbabhNO to anthracene, N2, and a (3)O atom is thermodynamically favorable at room temperature. Comparison of the OAT of adducts of N2O and MesCNO to the bulky complex 1 show a faster rate than in the case of free N2O or MesCNO despite increased steric hindrance of the adducts.

Minimization of the torsional barrier for phenyl ring flipping in a metal-organic framework (MOF) based on the new ethynyl-extended octacarboxylate ligand H(8)TDPEPE leads to a fluorescent material with a near-dark state. Immobilization of the ligand in the rigid structure also unexpectedly causes significant strain. We used DFT calculations to estimate the ligand strain energies in our and all other topologically related materials and correlated these with empirical structural descriptors to derive general rules for trapping molecules in high-energy conformations within MOFs. These studies portend possible applications of MOFs for studying fundamental concepts related to conformational locking and its effects on molecular reactivity and chromophore photophysics.

The title compound, [Mo(2)(C(11)H(16)N)(4)(C(10)H(11)N)(2)], is a dinuclear molybdenum complex with a formal metal-metal bond [Mo⋯Mo separation = 2.5946 (8) Å], four anilide-type ligands and two bridging mesityl nitrile groups. There are two inversion symmetric mol-ecules in the unit cell (an inversion center is localized at the mid-point of the Mo-Mo bond), each with approximate non-crystallographic C(2h) symmetry. The mol-ecules contain disordered isopropyl and 3,5-C(6)H(3)Me(2) groups on different anilido ligands; the major component having an occupancy of 0.683 (7). The complex was obtained in low yield as the product from the reaction between the bridging pyrazine adduct of molybdenum tris--anilide ([μ(2)-(C(4)H(4)N(2)){Mo(C(11)H(16)N)(3)}(2)]) and mesityl nitrile with a loss of one anilido ligand.

Facile methoxymethylation of N(2)-derived nitride NMo(N[(t)Bu]Ar)(3) provided the imido cation [MeOCH(2)NMo(N[(t)Bu]Ar)(3)](+) as its triflate salt in 88% yield. Treatment of the latter with LiN(SiMe(3))(2) provided blue methoxyketimide complex MeO(H)CNMo(N[(t)Bu]Ar)(3) in 95% yield. Conversion of the latter to the terminal cyanide complex NCMo(N[(t)Bu]Ar)(3), which was the subject of a single-crystal X-ray diffraction study, was accomplished in 51% yield upon treatment with a combination of SnCl(2) and Me(2)NSiMe(3).

The remarkable effect that secondary bonding interactions can have on the macroscopic properties of a material is illustrated by two polymorphs of the title compound. The phase which is most stable under ambient pressure and temperature consists of puckered supramolecular ribbon polymers assembled by Te--N secondary bonding interactions and displays a characteristic red-orange color. A second yellow phase consists of ribbons with alternating short and long intermolecular Te--N secondary bonding distances and is metastable; at 127 °C the material undergoes an exothermic irreversible transition to the red polymorph. A third phase consists of pyridine-solvated supramolecular dimers; it is also yellow and transforms into the red phase after the crystals effloresce. Computational DFT studies indicate that the observed changes in optical properties are related to intermolecular mixing of π orbitals enabled by the supramolecular interactions and the symmetry of the supramolecular synthon.

The He I photoelectron spectra of benzo-2,1,3-thia-, selena-, and telluradiazole were measured, and the observed ionization bands were assigned by comparison with the results of DFT calculations. Whereas the B3LYP exchange-correlation functional provided orbital energies that permitted a preliminary assignment by application of Koopman's theorem, a more-accurate interpretation was established by calculation of the vertical ionization energies with the PW91 functional and analysis of the correlation of energy levels along the homologous series. This strategy clarified earlier disagreements in the assignment of the spectrum of benzo-2,1,3-thiadiazole.

Being isoelectronic and isostructural analogues of N-alkyl-substituted telluradiazolyl cations, the adducts of triphenylborane with benzo-2,1,3-telluradiazole provide an electrically neutral point of reference with which the properties of the heterocyclic ions can be compared.