Hybrid Material Based on the Lindquist Polyoxometalate [W6O19]2− and the organosulfur donor o-Me2TTF: A Combined Structural and Spectroscopic Study

International audienceThe synthesis, crystal structure and spectroscopic properties of the hybrid radical cation salt containing oxidized o-3,4-dimethyltetrathiafulvalene (o-Me2TTF) and the Lindquist polyoxometalate anion [W6O19]2− are reported. The title salt represents the first time a Lindquist polyoxometalate has been utilized as the counter anion with this unsymmetrical member of the TTF family of derivatives. The salt crystallizes in the triclinic space group P1¯ with a = 7.6211(7) Å, b = 9.5231(9) Å, c = 12.2148(11) Å, α = 105.5870(10)°, β = 106.8340(10)° and γ = 95.6950(10)°. Resolution of the solid state structure revealed that the o-Me2TTF radical cations aggregate as isolated face-to-face dimers with intradimer interactions between neighboring sulfur atoms at distances <3.6 Å. Hydrogen bonding was also observed between hydrogen atoms bound to sp 2-hybridized carbon atoms of o-Me2TTF and bridging oxygen atoms of [W6O19]2−. Single crystal IR and Raman spectra were also collected and provide further evidence that the o-Me2TTF donors have been oxidized to their corresponding radical cationic states

Electron-molecular vibration coupling in (DMtTTF)Br and (o-DMTTF)2[W6O19] salts studied by vibrational spectroscopy

International audienceA novel 1:1 salt encompassing radical cations of DMtTTF (DMtTTF = dimethyltrimethylene-tetrathiafulvalene) and the Br−anion has been synthesized. Close inspection of the salt's solid state structure revealed the presence of quasi-isolated dimers containing DMtTTF radical cations, a specific arrangement whereby the microscopic parameters of DMtTTFradical dot+ might be studied. Analysis of the corresponding single crystal IR and Raman spectra of (DMtTTF)Br allowed us to study the material's electronic and vibrational structure and to evaluate the electron-molecular coupling constants via the isolated dimer model. Additionally, using previously published IR data, analogous calculations were performed on the salt (o-DMTTF)2[W6O19] (o-DMTTF = o-3,4-dimethyltetrathiafulvalene), which also contains well isolated dimers of o-DMTTF radical cations. These calculations revealed that the coupling constants for the unsymmetrical donors studied herein are comparable to those for symmetric TTF derivatives

Competing Supramolecular Forces: Boron Coordination vs π-π Stacking

This study explores the impact of fluorination levels in azopyridine Lewis bases on their ability to direct the formation of B←N coordination adducts or cocrystals with phenylboronic ester. We hypothesize that the degree of fluorination can be used as a tool to control the outcome of supramolecular bonding competition, thus influencing complex self-assembly. A series of azopyridines with varying degrees of fluorination were synthesized and reacted with phenylboronic ester. Their structures were analyzed using Hartree-Fock calculations, Hirshfeld surface analyses, and single crystal X-ray diffraction to assess the impact of fluorination on supramolecular interactions. The study reveals that azopyridines with up to two fluorine atoms form B←N coordination complexes, while perfluorinated azopyridine leads to cocrystal formation through π-stacking interactions. The outcome depends on the electronic properties of the pyridyl nitrogens, influenced by the level of fluorination. Fluorination in azopyridine Lewis bases serves as an effective strategy to modulate supramolecular bonding competition between boron coordination and π-stacking. This approach enables the selective formation of desired supramolecular structures, highlighting the utility of fluorination in guiding the self-assembly process. The findings have implications for the development of functional materials and 2D devices, offering a novel method for controlling the architecture of supramolecular assemblies

Confinement and Separation of Benzene from an Azeotropic Mixture Using a Chlorinated B←N Adduct

Separations of azeotropic mixtures are typically carried out using energy-demanding processes (e.g., distillation). Here, we report the capacity of a self-assembled chlorinated boronic ester-based adduct to confine acetonitrile and benzene in channels upon crystallization. The solvent confinement occurs via a combination of hydrogen bonding and [π···π] interactions. Quantitative separation of benzene from an azeotropic 1:1 mixture of a benzene/acetonitrile (v/v), and methanol is achieved through crystallization with the chlorinated adduct by complementary [C–H···O] and [C–H···π] interactions. Inclusion behavior is rationalized by molecular modeling and crystallographic analysis. The chlorinated boronic ester adduct shows the potential of modularity via isosteric substitution for the separation of challenging chemical mixtures (e.g., azeotropes)

Cupriphication of gold to sensitize d10–d10 metal–metal bonds and near-unity phosphorescence quantum yields

Outer-shell s0/p0 orbital mixing with d10 orbitals and symmetry reductionuponcupriphicationofcyclic trinucleartrigonal-planargold(I) complexes are found to sensitize ground-state Cu(I)–Au(I) covalent bonds and near-unity phosphorescence quantum yields. Heterobimetallic Au4Cu2 {[Au4(μ-C2,N3-EtIm)4Cu2(μ-3,5-(CF3)2Pz)2], (4a)}, Au2Cu {[Au2(μ-C2,N3-BzIm)2Cu(μ-3,5-(CF3)2Pz)], (1) and [Au2(μ-C2, N3-MeIm)2Cu(μ-3,5-(CF3)2Pz)], (3a)}, AuCu2 {[Au(μ-C2,N3-MeIm)Cu2(μ3,5-(CF3)2Pz)2], (3b) and [Au(μ-C2,N3-EtIm)Cu2(μ-3,5-(CF3)2Pz)2], (4b)} and stacked Au3/Cu3 {[Au(μ-C2,N3-BzIm)]3[Cu(μ-3,5-(CF3)2Pz)]3, (2)} formuponreactingAu3 {[Au(μ-C2,N3-(N-R)Im)]3 ((N-R)Im = imidazolate; R =benzyl/methyl/ethyl =BzIm/MeIm/EtIm)} with Cu3 {[Cu(μ-3,5(CF3)2Pz)]3 (3,5-(CF3)2Pz = 3,5-bis(trifluoromethyl)pyrazolate)}. The crystal structures of 1 and 3a reveal stair-step infinite chains whereby adjacent dimer-of-trimer units are noncovalently packed via twoAu(I)⋯Cu(I)metallophilicinteractions,whereas 4a exhibitsa hexanuclear cluster structure wherein two monomer-of-trimer units are linked by a genuine d10–d10 polar-covalent bond with ligandunassisted Cu(I)–Au(I) distances of 2.8750(8) Å each—the shortest such an intermolecular distance ever reported between any two d10 centers so as to deem it a “metal–metal bond” vis-à-vis “metallophilic interaction.” Density-functional calculations estimate 35– 43kcal/molbindingenergy,akintotypicalM–Msingle-bondenergies. Congruently, FTIR spectra of4a showmultiple far-IR bands within 65– 200 cm−1, assignable to vCu-Au as validated by both the Harvey–Gray method of crystallographic-distance-to-force-constant correlation and dispersive density functional theory computations. Notably, the heterobimetallic complexes herein exhibit photophysical properties that are favorable to those for their homometallic congeners, due to threefold-to-twofold symmetry reduction, resulting in cuprophilicsensitizationinextinctioncoefficientandsolid-state photoluminescence quantum yields approaching unity (ΦPL = 0.90–0.97 vs. 0–0.83 for Au3 and Cu3 precursors), which bodes well for potential future utilization in inorganic and/or organic LED applications

Catalytic intramolecular hydroamination of aminoallenes using titanium complexes of chiral, tridentate, dianionic imine-diol ligands

Alkylation of D- or L-phenylalanine or valine alkyl esters was carried out using methyl or phenyl Grignard reagents. Subsequent condensation with salicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, or 5-fluorosalicylaldehyde formed tridentate, X_2L type, Schiff base ligands. Chiral shift NMR confirmed retention of stereochemistry during synthesis. X-ray crystal structures of four of the ligands show either inter- or intramolecular hydrogen bonding interactions. The ligands coordinate to the titanium reagents Ti(NMe_2)_4 or TiCl(NMe_2)_3 by protonolysis and displacement of two equivalents of HNMe_2. The crystal structure of one example of Ti(X_2L)Cl(NMe_2) was determined and the complex has a distorted square pyramidal geometry with an axial NMe_2 ligand. The bis-dimethylamide complexes are active catalysts for the ring closing hydroamination of di- and trisubstituted aminoallenes. The reaction of hepta-4,5-dienylamine at 135 °C with 5 mol% catalyst gives a mixture of 6-ethyl-2,3,4,5-tetrahydropyridine (40–72%) and both Z- and E-2-propenyl-pyrrolidine (25–52%). The ring closing reaction of 6-methyl-hepta-4,5-dienylamine at 135 °C with 5 mol% catalyst gives exclusively 2-(2-methyl-propenyl)-pyrrolidine. The pyrrolidine products are obtained with enantiomeric excesses up to 17%

Increase of Direct C-C Coupling Reaction Yield by Identifying Structural and Electronic Properties of High-Spin Iron Tetra-azamacrocyclic Complexes

Macrocyclic ligands have been explored extensively as scaffolds for transition metal catalysts for oxygen and hydrogen atom transfer reactions. C–C reactions facilitated using earth abundant metals bound to macrocyclic ligands have not been well-understood but could be a green alternative to replacing the current expensive and toxic precious metal systems most commonly used for these processes. Therefore, the yields from direct Suzuki–Miyaura C–C coupling of phenylboronic acid and pyrrole to produce 2-phenylpyrrole facilitated by eight high-spin iron complexes ([Fe3+L1(Cl)2]+, [Fe3+L4(Cl)2]+, [Fe2+L5(Cl)]+, [Fe2+L6(Cl)2], [Fe3+L7(Cl)2]+, [Fe3+L8(Cl)2]+, [Fe2+L9(Cl)]+, and [Fe2+L10(Cl)]+) were compared to identify the effect of structural and electronic properties on catalytic efficiency. Specifically, catalyst complexes were compared to evaluate the effect of five properties on catalyst reaction yields: (1) the coordination requirements of the catalyst, (2) redox half-potential of each complex, (3) topological constraint/rigidity, (4) N atom modification(s) increasing oxidative stability of the complex, and (5) geometric parameters. The need for two labile cis-coordination sites was confirmed based on a 42% decrease in catalytic reaction yield observed when complexes containing pentadentate ligands were used in place of complexes with tetradentate ligands. A strong correlation between iron(III/II) redox potential and catalytic reaction yields was also observed, with [Fe2+L6(Cl)2] providing the highest yield (81%, −405 mV). A Lorentzian fitting of redox potential versus yields predicts that these catalysts can undergo more fine-tuning to further increase yields. Interestingly, the remaining properties explored did not show a direct, strong relationship to catalytic reaction yields. Altogether, these results show that modifications to the ligand scaffold using fundamental concepts of inorganic coordination chemistry can be used to control the catalytic activity of macrocyclic iron complexes by controlling redox chemistry of the iron center. Furthermore, the data provide direction for the design of improved catalysts for this reaction and strategies to understand the impact of a ligand scaffold on catalytic activity of other reactions

Crystal Structure of the Radical-Cation Salt (o-Me2TTF)I3 with Close Intermolecular Sulfur Contacts.

International audienceThe synthesis and crystal structure of the org. radical-cation salt (o-Me2TTF)I3 is described. The salt crystallizes in the monoclinic space group P2 1 /n with a = 10.927(2) Å, b = 11.904(2) Å, c = 12.660(2) Å, β = 115.174(5)°. The bond length of the central C=C bond in o-Me2TTF is 1.401(1) Å, indicating an approx. oxidn. state of +1 for the o-Me2TTF radical cation. Graphical Abstr. The X-ray crystallog. structure of the radical cation salt (o-Me2TTF)I3 has been detd. and its structural properties and synthetic prepn. are discussed

Halogen-Bond Mediated [2+2] Photodimerizations: À la Carte Access to Unsymmetrical Cyclobutanes in the Solid State

The ditopic halogen-bond (X-bond) donors 1,2-, 1,3-, and 1,4-diiodotetrafluorobenzene (1,2-, 1,3-, and 1,4-di-I-tFb, respectively) form binary cocrystals with the unsymmetrical ditopic X-bond acceptor trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene (2,4-bpe). The components of each cocrystal (1,2-di-I-tFb)·(2,4-bpe), (1,3-di-I-tFb)·(2,4-bpe), and (1,4-di-I-tFb)·(2,4-bpe) assemble via N···I X-bonds. For (1,2-di-I-tFb)·(2,4-bpe) and (1,3-di-I-tFb)·(2,4-bpe), the X-bond donor supports the C=C bonds of 2,4-bpe to undergo a topochemical [2+2] photodimerization in the solid state: UV-irradiation of each solid resulted in stereospecific, regiospecific, and quantitative photodimerization of 2,4-bpe to the corresponding head-to-tail (ht) or head-to-head (hh) cyclobutane photoproduct, respectively

(S)-2-[(4-Fluoro­phen­yl)formamido]-3-phenyl­propanoic acid

The title compound, C(16)H(14)FNO(3), was synthesized via solid phase methods; it exhibits monoclinic (P2(1)) symmetry at room temperature. The two independent mol­ecules that comprise the asymmetric unit display distinct torsion angles of 173.2 (2) and 72.6 (2)° along the central sp (3) C—N bond. In the crystal, hydrogen bonding through N—H⋯O contacts couples the asymmetric unit mol­ecules into pairs that align in layers extending parallel to (100) via additional O—H⋯O inter­actions. The phenyl ring of one independent mol­ecule was found to be disordered over two sets of sites in a 0.55 (3):0.45 (3) ratio. [Image: see text