Coordination-Induced Band Gaps in MOFs

Herein, we report on the synthesis of a microporous, three-dimensional phosphonate metal-organic framework (MOF) of the composition Cu3(H5-MTPPA)2·2 NMP (H8-MTPPA = methane tetra-p-phenylphosphonic acid and NMP = N-methyl-2-pyrrolidone). This MOF, termed TUB1, has a unique one-dimensional inorganic building unit composed of square planar and distorted trigonal bipyramidal copper atoms. It possesses a (calculated) BET surface area of 766.2 m2/g after removal of the solvents from the voids. The Tauc plot for TUB1 yields indirect and direct band gaps of 2.4 eV and 2.7 eV, respectively. DFT calculations reveal the existence of two spin-dependent gaps of 2.60 eV and 0.48 eV for the alpha and beta spins, respectively, with the lowest unoccupied crystal orbital for both gaps predominantly residing on the square planar copper atoms. The projected density of states suggests that the presence of the square planar copper atoms reduces the overall band gap of TUB1, as the beta-gap for the trigonal bipyramidal copper atoms is 3.72 eV.

Tris[triphenylantimony(V)]hexa(μ-oxido)tellurium(VI): a molecular complex with six Te—O—Sb bridges

In the structure of the title compound [systematic name hexa-μ-oxido-1:2κ4 O:O;1:3κ4 O:O;1:4κ4 O:O-nonaphenyl-2κ3 C,3κ3 C,4κ3 C-triantimony(V)tellurium(VI)], [Sb3Te(C6H5)9O6], the hexaoxidotellurate(VI) ion is coordinated to three SbV ions via pairs of cis-positioned O atoms to form a discrete molecular unit. The TeVI and SbV central ions exhibit distorted octahedral [TeO6] and distorted trigonal–bipyramidal [SbC3O2] coordination geometries, respectively. The linking of these polyhedra, by sharing the dioxide edges, results in the Te-based octahedron having a mer-configuration. The packing of the molecules is dominated by C—H...O hydrogen bonding and weak dispersion forces, with a minor contribution from C—H...π bonds and π–π stacking interactions. According to the Hirshfeld surface analysis, the contributions of the H...H, H...C/C...H and H...O/O...H contacts are 58.0, 32.6 and 7.8%, respectively. The title structure provides a model for the bonding of triorganoantimony dications to octahedral oxoanions, and the observed doubly bridged motifs, Te(μ-O)2Sb, may find application in the functionalization of polyoxometalate species.

Co(II) Amide, Pyrrolate, and Aminopyridinate Complexes: Assessment of their Manifold Structural Chemistry and Thermal Properties

A series of cobalt(II) (silyl)amides, pyrrolates and aminopyridinates were synthesized. Inspired by the dimeric bis(trimethylsilylamido)cobalt(II) complex ([Co(TMSA)2]2), facile salt metathesis employing the ligand 2,2,5,5-tetramethyl-1,2,5-azadisilolidinyl (TMADS) yielded its congener [Co(TMADS)2]2. Novel, heteroleptic Lewis adducts of the former resulted in unusual three- to four-fold coordination geometry around the metal center. Similarily, the salt [Co(TMADS)3Li(DAD)2] was isolated which demonstrates an ion separated Co(II) anion with silylamide ligation and Li+ counter cation. Transpyrrolylation using [Co(TMSA)2]2 was established for the synthesis of bis[N,N’-2-(dimethylaminomethyl)pyrrolyl]cobalt(II), and bis(N-2-(tert-butyliminomethyl)pyrrolyl)cobalt(II). Treatment of CoCl2 with two equivalents of lithiated N,N-dimethyl(N’-tert-butyl)ethane-1-amino-2-amide and N,N-dimethyl(N’-trimethylsilyl)ethane-1-amino-2-amide resulted in the respective Co(II) amido-amines. Reaction of CoCl2 with lithium 4-methyl-N-(trimethylsilyl)pyridine-2-amide yielded the first binuclear, homoleptic Co(II) aminopyridinate complex with a distorted trigonal bipyramidal coordination environment (τ5 = 0.533) for one central Co(II) ion and a weakly distorted tetrahedral coordination geometry (τ4 = 0.845) for the other. All of the new compounds were thoroughly characterized in terms of composition and structure. Finally, the key thermal characteristics of volatility and thermal stability were assessed using a combination of thermogravimetric analysis and complementary bulk sublimation experiments.

Experimental and Computational Investigations into Trivalent Phosphorous-Mediated Radical Thiol Desulfurization

Radical-mediated thiol desulfurization processes using tricoordinate phosphorous reagents are used in a range of applications from small molecule synthesis to peptide modification. A combined experimental and computational examination of the mechanism and kinetics of the radical desulfurization of alkyl thiyl radicals using trivalent phosphorus reagents was performed. Primary alkyl thiols undergo desulfurization between 10^6 to 10^9 M-1s-1 depending on the phosphorus component with either an H-atom transfer step or β-fragmentation of the thiophosphoranyl intermediate may be rate-controlling. While the desulfurization of primary aliphatic thiols showed a marked dependence on the identity of phosphorous reagent used with either a rate-controlling H-atom transfer or -fragmentation, thiols yielding stabilized C-centered radicals showed much less sensitivity. Support for a stepwise S-atom transfer process progressing via a distorted trigonal bipyramidal thiophosphoranyl radical intermediate was obtained from DFT calculated energetics and hyperfine splitting values.

Hypercoordinated Organotin(IV) Compounds Containing ĸ²-C,O- And ĸ²,N- Chelating Ligands: Synthesis, Characterization, and Polymerization Behaviour

Rigid homopolystannanes and alternating polystannanes containing a benzyl methoxy ether (C,O) or benzyl dimethyl amine (C,N) ligand were prepared using either a direct approach, lithiation and transmetallation, or an alternative approach, either sequential chlorinations or brominations. X-ray crystallographic studies of 41 and 45 were conducted to find 41 in a distorted tetrahedral geometry with moderate hypercoordinate interaction (Sn-N: 2.917 Å) while 45 in a distorted trigonal bipyramidal with strong hypercoordinate interaction (Sn-N: 2.403 Å). Hydrogenation of 31 and 33 produced 42 and 43 in moderate-to-good yields. Dehydrocoupling polymerization produced modest molecular weight, rigid C,O- (Mw = 3.03 × 10⁴ Da, PDI: 1.4) and C,N- (Mw = 3.10 × 10⁴ Da, PDI: 1.82) homopolymers 56 and 57. Finally, condensation polymerization was attempted to produce low molecular weight (Mw = 1.30 × 10⁴ Da, PDI: 2.0) C,O- alternating polymer 60 and oligomer 61 (Mw = 0.92 × 10⁴ Da, PDI: 2.71).

Hypercoordinated Organotin(IV) Compounds Containing ĸ²-C,O- And ĸ²,N- Chelating Ligands: Synthesis, Characterization, and Polymerization Behaviour

Rigid homopolystannanes and alternating polystannanes containing a benzyl methoxy ether (C,O) or benzyl dimethyl amine (C,N) ligand were prepared using either a direct approach, lithiation and transmetallation, or an alternative approach, either sequential chlorinations or brominations. X-ray crystallographic studies of 41 and 45 were conducted to find 41 in a distorted tetrahedral geometry with moderate hypercoordinate interaction (Sn-N: 2.917 Å) while 45 in a distorted trigonal bipyramidal with strong hypercoordinate interaction (Sn-N: 2.403 Å). Hydrogenation of 31 and 33 produced 42 and 43 in moderate-to-good yields. Dehydrocoupling polymerization produced modest molecular weight, rigid C,O- (Mw = 3.03 × 10⁴ Da, PDI: 1.4) and C,N- (Mw = 3.10 × 10⁴ Da, PDI: 1.82) homopolymers 56 and 57. Finally, condensation polymerization was attempted to produce low molecular weight (Mw = 1.30 × 10⁴ Da, PDI: 2.0) C,O- alternating polymer 60 and oligomer 61 (Mw = 0.92 × 10⁴ Da, PDI: 2.71).

Crystal structure refinement of magnesium zinc divanadate, MgZnV2O7, from powder X-ray diffraction data

The crystal structure of magnesium zinc divanadate, MgZnV2O7, was determined and refined from laboratory X-ray powder diffraction data. The title compound was synthesized by a solid-state reaction at 1023 K in air. The crystal structure is isotypic with Mn0.6Zn1.4V2O7 (C2/m; Z = 6) and is related to the crystal structure of thortveitite. The asymmetric unit contains two metal sites with statistically distributed magnesium and zinc atoms with the atomic ratio close to 1:1. One (Mg/Zn) metal site (M1) is located on Wyckoff position 8j and the other (M2) on 4h. Three V sites (all on 4i), and eight O (three 8j, four 4i, and one 2b) sites complete the asymmetric unit. The structure is an alternate stacking of V2O7 layers and (Mg/Zn) atom layers along [20\overline{1}]. It is distinct from other related structures in that each V2O7 layer consists of two groups: a V2O7 dimer and a V4O14 tetramer. Mixed-occupied M1 and M2 are coordinated by oxygen atoms in distorted trigonal bipyramidal and octahedral sites, respectively.

Chiral crystallization of a zinc(II) complex

The compound, {6,6′-dimethoxy-2,2′-[(4-azaheptane-1,7-diyl)bis(nitrilomethanylidyne)]diphenolato}zinc(II) methanol monosolvate, [Zn(C22H27N3O4)]·CH3OH, at 298 K crystallizes in the orthorhombic space group Pna21. The Zn atom is coordinated by a pentadentate Schiff base ligand in a distorted trigonal–bipyramidal N3O2 geometry. The equatorial plane is formed by the two phenolic O and one amine N atom. The axial positions are occupied by two amine N atoms. The distorted bipyramidal geometry is also supported by the trigonality index (τ), which is found to be 0.85 for the molecule. In the crystal, methanol solvent molecule is connected to the complex molecule by an O—H...O hydrogen bond and the complex molecules are connected by weak supramolecular interactions, so achiral molecules generate a chiral crystal. The Hirshfeld surface analysis suggests that H...H contacts account for the largest percentage of all interactions.

A 3D Cu-Phosphonate Metal-Organic Framework with Cu-Coordination-Enhanced Electrical Conductivity

Herein, we report on the synthesis and electronic properties of the phosphonate metal-organic framework (MOF) Cu₃(H₅-MTPPA)₂ (H₈-MTPPA = methane tetra-<i>p</i>-phenylphosphonic acid). This MOF, termed TUB1, has a unique one-dimensional inorganic building unit composed of square planar and distorted trigonal bipyramidal copper atoms, and a calculated BET surface area of 766.2 m²/g. The formation of TUB1 reduces the band gap of the linker from 4.2 eV to 2.4 eV. DFT calculations reveal two spin-dependent gaps of 2.60 eV and 0.48 eV for the alpha and beta spins, respectively, and that the lowest unoccupied crystal orbital<b> </b>for both gaps predominantly resides on the square planar copper atoms. Single-crystal conductivity measurements on TUB1 crystals yield an average electrical conductance of 53.2 ± 29.5 S/m. Although the H₈-MTPPA linker blocks the extended conjugation in TUB1, we show that the presence of the square planar copper atoms in the inorganic building unit promotes the electrical conductivity.

A 3D Cu-Phosphonate Metal-Organic Framework with Cu-Coordination-Enhanced Electrical Conductivity

Herein, we report on the synthesis and electronic properties of the phosphonate metal-organic framework (MOF) Cu₃(H₅-MTPPA)₂ (H₈-MTPPA = methane tetra-<i>p</i>-phenylphosphonic acid). This MOF, termed TUB1, has a unique one-dimensional inorganic building unit composed of square planar and distorted trigonal bipyramidal copper atoms, and a calculated BET surface area of 766.2 m²/g. The formation of TUB1 reduces the band gap of the linker from 4.2 eV to 2.4 eV. DFT calculations reveal two spin-dependent gaps of 2.60 eV and 0.48 eV for the alpha and beta spins, respectively, and that the lowest unoccupied crystal orbital<b> </b>for both gaps predominantly resides on the square planar copper atoms. Single-crystal conductivity measurements on TUB1 crystals yield an average electrical conductance of 53.2 ± 29.5 S/m. Although the H₈-MTPPA linker blocks the extended conjugation in TUB1, we show that the presence of the square planar copper atoms in the inorganic building unit promotes the electrical conductivity.