Molecular Alumo- and Gallosilicate Hydrides Functionalized with Terminal M(NR2)3 and Bridging M(NR2)2 (M = Ti, Zr, Hf; R = Me, Et) Moieties.

A general synthetic strategy for the systematic synthesis of group 4 MIV heterometallic complexes LMIII(H)(µ-O)Si(µ-O)(OtBu)2}nMIV(NR2)4-n (L = {[HC{C(Me)N(2,6-iPr2C6H3)}2; MIII = Al or Ga; n = 1 or 2; MIV = Ti, Zr, Hf; R = Me, Et), based on alumo- or gallosilicate hydride ligands bearing a Si-OH moiety, is presented. The challenging isolation of these metalloligands involved two strategies. On the one hand, the acid-base reaction of LAlH2 with (HO)2Si(OtBu)2 yielded LAlH(µ-O)Si(OH)(OtBu)2 (1), while on the other hand, the oxidative addition of (HO)2Si(OtBu)2 to LGa produced the gallium analog (2). These metalloligands successfully stabilized two hydrogen atoms with different acid-base properties (MIII-H and SiO-H) in the same molecule. Reactivity studies between 1 and 2 and group 4 amides MIV(NR2)4 (MIV = Ti, Zr, Hf; R = Me, Et) and tuning the reactions conditions and stoichiometry led to isolation and structural characterization of heterometallic complexes 3-11 with a 1:1 or 2:1 metalloligand/MIV ratio. Notably, some of these molecular heterometallic silicate complexes stabilize for the first time terminal (O3Si-O-)MIV(NR2)3 moieties known from single-site silica-grafted species. Furthermore, the aluminum-containing heterometallic complexes possess Al-H vibrational energies similar to those reported for modified alumina surfaces, which makes them potentially suitable models for the proposed MIV species grafted onto silica/alumina surfaces with hydride and dihydride architectures.

(1S,3R)-N-{(3S,10S,12S,13R,17R)-12-Hy-droxy-17-[(R)-5-hy-droxy-pentan-2-yl]-10,13-di-methyl-hexa-deca-hydro-1H-cyclo-penta-[a]phenanthren-3-yl}adamantane-1-carboxamide 0.25-hydrate.

The title compound, C35H57NO3·0.25H2O, was synthesized from de-oxy-cholic acid followed by a protection, a Mitsonobu substitution, a Staudinger reduction, formation of an amide and final reduction in the lateral chain. The compound crystallizes in the P1 space group with four steroid mol-ecules and one water mol-ecule in the triclinic cell unit. The crystal structure features O-H⋯O hydrogen bonding. The crystal studied was refined as a non-merohedral twin.

Benzene and Borazine, so Different, yet so Similar: Insight from Experimental Charge Density Analysis.

Although benzene and borazine are isoelectronic and isostructural, they have very different electronic structures, mainly due to the polar nature of the B-N bond. Herein, we present an experimental study of the charge density distribution obtained from the multipole model formalism and Hirshfeld atom refinement (HAR) based on high-resolution X-ray diffraction data of borazine B3N3H6 (1) and B,B',B″-trichloroborazine (2) crystals. These data are compared to those obtained from HAR for benzene (4) and 1,3,5-trichlorobenzene (5) and further compared with values obtained from density functional theory calculations in the gas phase, where N,N',N″-trichloroborazine (3) was also included. The results confirm that, unlike benzene, borazines are only weakly aromatic with an island-like electronic delocalization within the B3N3 ring involving only the nitrogen atoms. Furthermore, delocalization indices and interacting quantum atom energy for bonded and non-bonded atoms were found to be highly suitable indicators capable of describing the origin of the discrepancies observed when the degree of aromaticity in 2 and 3 is evaluated using common aromaticity indices. Additionally, analysis of intermolecular interactions in the crystals brings further evidence of a weakly aromatic character of the borazines as it reveals surprising similarities between the crystal packing of borazine and benzene and also between B,B',B″-trichloroborazine and 1,3,5-trichlorobenzene.

Hetero-bimetallic alkali titanosilicates [MOTi{OSi(OtBu)3}3]2 (M = Li-Cs) with terminal Ti-O- groups.

The molecular titanosilicate [(tBuO3)3SiO]3TiNEt2 (1) was obtained from the reaction between silanol (tBuO3)3SiOH and titanium amide Ti(NEt2)4. The reaction of 1 with alkali metal hydroxides MOH (M = Li, Na, K, Rb, Cs) offers a straightforward route to the alkaline salts of titanosilicates [MOTi{OSi(OtBu)3}3]2 with a terminal Ti-O- moiety. All compounds were characterised by single-crystal X-ray diffraction studies. Hirshfeld atom refinement and QTAIM analysis of the electron density in 1 and in the Rb salt 5 revealed the D-A nature of the Ti-O and Ti-N bonds and the presence of agostic C-H⋯Rb interactions.

Crystal structure of caesium tetra-methyl-dithio-imidodiphosphinate.

In the title crystal, the salt [CsMe2P(S)NP(S)Me2] is self-assembled as an undulating supra-molecular two-dimensional polymeric structure, poly[(µ4-tetra-methyl-dithio-imidodiphosphinato)caesium], [Cs(C4H12NP2S2)] n , which is parallel to the bc plane. The Cs cations are hexa-coordinated, being chelated by two thio-imidophosphinate groups and two sulfur atoms from neighboring ligands. The anions are linked to the Cs cations by Cs⋯S and Cs⋯N electrostatic inter-actions.

Capture of toxic gases in MOFs: SO2, H2S, NH3 and NO x.

MOFs are promising candidates for the capture of toxic gases since their adsorption properties can be tuned as a function of the topology and chemical composition of the pores. Although the main drawback of MOFs is their vulnerability to these highly corrosive gases which can compromise their chemical stability, remarkable examples have demonstrated high chemical stability to SO2, H2S, NH3 and NO x . Understanding the role of different chemical functionalities, within the pores of MOFs, is the key for accomplishing superior captures of these toxic gases. Thus, the interactions of such functional groups (coordinatively unsaturated metal sites, µ-OH groups, defective sites and halogen groups) with these toxic molecules, not only determines the capture properties of MOFs, but also can provide a guideline for the desigh of new multi-functionalised MOF materials. Thus, this perspective aims to provide valuable information on the significant progress on this environmental-remediation field, which could inspire more investigators to provide more and novel research on such challenging task.

Non-Covalent Interactions in the Biphenyl Crystal: Is the Planar Conformer a Transition State?

A combined experimental and theoretical study of the biphenyl (BP) crystal is presented. The X-ray diffraction data collected at 100 K were subjected to Hirshfeld atom and multipole refinements of the electron density, ρ(r). A theoretical exploration of the potential energy surface (PES) of the crystal was also carried out. This investigation challenges the common assumption that the planar structure of BP in the phase I crystal is an average of two twisted configurations in a double-well potential. The theoretical computations provide compelling evidence that this structure corresponds to a minimum on the PES hence to a stable molecular arrangement. Consistently, the experiment showed no evidence of positional or dynamic disorder. The intramolecular hydrogen-hydrogen bonds detected are not repulsive. The topological analysis of the experimental and theoretical ρ(r) reveals that both the intra- and intermolecular H⋅⋅⋅H and the C-H⋅⋅⋅π contacts stabilize the BP crystal.

SO2 Capture Using Porous Organic Cages.

We report the first experimental investigation of porous organic cages (POCs) for the demanding challenge of SO2 capture. Three structurally related N-containing cage molecular materials were studied. An imine-functionalized POC (CC3) showed modest and reversible SO2 capture, while a secondary-amine POC (RCC3) exhibited high but irreversible SO2 capture. A tertiary amine POC (6FT-RCC3) demonstrated very high SO2 capture (13.78 mmol g-1 ; 16.4 SO2 molecules per cage) combined with excellent reversibility for at least 50 adsorption-desorption cycles. The adsorption behavior was investigated by FTIR spectroscopy, 13 C CP-MAS NMR experiments, and computational calculations.

SO2 Capture and Oxidation in a Pd6L8 Metal-Organic Cage.

The facile and green preparation of novel materials that capture sulfur dioxide (SO2) with significant uptake at room temperature remains challenging, but it is crucial for public health and the environment. Herein, we explored for the first time the SO2 adsorption within microporous metal-organic cages using the palladium(II)-based [Pd6L8](NO3)36 tetragonal prism 1, assembled in water under mild conditions. Notably and despite the low BET surface area of 1 (111 m2 g-1), sulfur dioxide was found to be irreversibly and strongly adsorbed within the activated cage at 298 K (up to 6.07 mmol g-1). The measured values for the molar enthalpy of adsorption (ΔHads) coupled to the FTIR analyses imply a chemisorption process that involves the direct interaction of SO2 with Pd(II) sites and the subsequent oxidation of this toxic chemical by the action of the nitrate anions in 1. To the best of our knowledge, this is the first reported metal-organic cage that proves useful for SO2 adsorption. Metallosupramolecular adsorbents such as 1 could enable new detection applications and suggest that the integration of soft metal ions and self-assembly of molecular cages are a potential means for the easy tuning of SO2 adsorption capabilities and behavior.

Aluminum-Triggered Condensation of Vicinal Silicate Groups into a Bicyclic Alumosilicate.

The molecular alumosilicates AlL{OSi(OtBu)2O}[OSi{(µ3-O)(MR2)2(µ-OtBu)}(OtBu)] (L = HC[CMeNAr]2-, where M = Al, R = Me (2), Et (3), and iBu (4) and M = Ga, R = Me (5)) were obtained from the reaction of AlL{OSi(OtBu)2(OH)}2 (1) with 1 or 2 equiv of the respective organometallic precursor. These compounds have a central bicyclic inorganic core formed by a six-membered AlSi2O3 alumosilicate ring with a Si-O-Si unit connected via a Si-O bond to a four-membered Al2O2 alumoxane ring. These compounds are formed even though 1 is specifically designed to yield 4R alumosilicate rings that would obey the Löweinstein's and Dempsey's rules about concatenation between silicon and aluminum tetrahedra in alumosilicates. We propose a mechanism for this rearrangement, based on the experimental evidence and density functional theory calculations, that involves a κ3µ2 coordination of a silicate unit to two AlMe2 groups, which weakens one Si-O bond and explains how aluminum atoms can cleave Si-O bonds. Furthermore, formation of the products experimentally confirms the theory that Al-O-Al groups can exist in alumosilicates if the oxygen atom belongs to an OH moiety.

Partially Reversible H2S Adsorption by MFM-300(Sc): Formation of Polysulfides.

The metal-organic framework (MOF)-type MFM-300(Sc) exhibits a combined physisorption and chemisorption capture of H2S, leading to a high uptake (16.55 mmol g-1) associated with high structural stability. The irreversible chemisorbed sulfur species were identified as low-order polysulfide (n = 2) species. The isostructural MFM-300(In) was demonstrated to promote the formation of different polysulfide species, paving the way toward a new methodology to incorporate polysulfides within MOFs for the generation of novel MOF-lithium/sulfur batteries.

Synthesis of bicyclic 1,4-thiazepines as novel anti-Trypanosoma brucei brucei agents.

1,4-Thiazepines derivatives are pharmacologically important heterocycles with different applications in medicinal chemistry. In the present work, we describe the preparation of new bicyclic thiazolidinyl-1,4-thiazepines 3 by reaction between azadithiane compounds and Michael acceptors. The reaction scope was explored and the yields were optimized. The activity of the new compounds was evaluated against Nippostrongylus brasiliensis and Caenorhabditis elegans as anthelmintic models and Trypanosoma brucei brucei. The most active compound was 3l, showing an EC50 = 2.8 ± 0.7 µM against T. b. brucei and a selectivity index >71.

Reactivity patterns for the activation of CO2 and CS2 with alumoxane and aluminum hydrides.

Carbon dioxide is readily fixed when reacting with either alumoxane dihydride [{MeLAl(H)}2(µ-O)] (1) or aluminum dihydride [MeLAlH2] (2) (MeL = HC[(CMe)N(2,4,6-Me3C6H2)]2-) to produce bimetallic aluminum formates [(MeLAl)2(µ-OCHO)2(µ-O)] (3) and [(MeLAl)2(µ-OCHO)2(µ-H)2] (5), respectively. Furthermore, [(MeLAl)2(µ-OCHO)2(µ-OH)2] (4) is easily obtained upon the reaction of 3 or 5 with H2O. The stability of the unusual dialuminum diformate dihydride core observed in 5 stems from the proximity of the Al centers allowing the formation of two Al-HAl bridges and precluding further hydride transfer to the HCO2 moieties. Contrary to this behavior, 1 and 2 react with CS2 giving cyclic alumoxane and aluminum sulfides [(MeLAl)2(µ-S)(µ-O)] (6) and [{MeLAl(µ-S)}2] (7), respectively. The molecular structures of 3-7 were characterized by IR, Raman, solution or solid-state (MAS) NMR spectroscopy and mass spectrometry and for 4-7 were characterized by X-ray diffraction studies. NMR kinetic studies and DFT calculations suggest that the mechanisms for the formation of 6 and 7 involve the transfer of a hydride group forming transient aluminum thioformate intermediates which proceed to form Al-S-Al moieties through the cleavage of C-S bonds and insertion of a sulfur atom, followed by the elimination of thioformaldehyde.

Metal-directed self-assembly of transition metal heterometallascorpionates.

The heterobimetallic complexes [Co(LtzE)3K(THF)2] [LtzE = [{4,5-(P(E)Ph2)2}tz]-; tz = 1,2,3-triazole; E = S(3), Se(4)] featuring high-spin cobalt centres, and [Ni(LtzE)3K(THF)2] [E = S(5), Se(6)] were synthesized through the self-assembly reaction of HLtzE [E = S(1), Se(2)], KOH or K0 and MCl2 (M = Co, Ni). Compounds 3-6 exhibit an unusual metallascorpionate-type anion formed by the coordination of three triazole units via a κ2-N,E mode to the transition-metal atom, and this anion further coordinates to a potassium cation through a κ3-N',N'',N''' fashion. Compounds 3 and 5 were used in the synthesis of 3d-metal heterometallascorpionates [M(LtzS)3Cu(PPh3)] [M = Co, (7), M = Ni (8)] and the bimetallic complex [Ni(LtzE)3Ni(NO3)(THF)] (9) through metathesis reactions, pointing to stable metallascorpionate anions in solution. The solution behavior of 3-9 was investigated by UV-visible spectroscopy, high-resolution mass spectrometry, electrochemical methods and by magnetic-susceptibility measurements. The molecular structures of 3-6, 8 and 9 were determined by single-crystal X-ray diffraction studies and exhibit MM' distances ranging from 3.52 to 3.88 Å.

A Chiral Bis-Naphthylated Tetrandrine Dibromide: Synthesis, Self-Assembly into an Organic Framework Based On Nanosized Spherical Cages, and Inclusion Studies.

Crystalline framework materials have gained interest because of their many potential applications. A novel chiral tetrandrine salt (DNT) has been synthesized and characterized by conventional analytical techniques and single-crystal X-ray diffraction analysis, and its self-assembly behavior studied. In the solid state, 48 molecules of the compound self-assemble into an organic framework based on nanospherical aggregates formed exclusively through weak noncovalent interactions. Additionally, it was demonstrated by UV-vis spectroscopy and TGA that assembled DNT can include the Nile Red dye, giving a fluorescent material. To the best of our knowledge, these spherical assemblies are the largest among the purely synthetic organic self-assembled molecular crystals reported to date.

Self-Assembly of Aluminum- and Gallium-Based meso-Metallaporphyrins.

The molecular meso-metallaporphyrin has been obtained from the reaction of AlMe3 with the bulky 4,5-(Ph2(HO)C)2-1,2,3-triazole (1). The presence of Al-Me groups coordinated to the triazole rings creates three different stereoisomers that were identified by single-crystal X-ray diffraction. Further studies revealed that, for steric reasons, only one of the two main stereoisomers is active in the polymerization of ε-caprolactone. When GaMe3 is used instead of AlMe3, a trimetallic species is formed instead of the meso-metallaporphyrin pointing to a metal-directed self-assembly. On the other hand, the reaction of the monolithium salt [{Li(THF)2}{κ2- N, N'-4,5-(Ph2(HO)C)-1,2,3-triazole}]2 (2; THF = tetrahydrofuran) with MCl3 (M = Al, Ga) yields meso-metallaporphyrin species with a lithium atom in the center of the metallacycle. While the gallium derivative is rather stable in solution, the aluminum analogue decomposes rapidly. In the solid state, continuous cationic columns running throughout the whole crystal are formed from alternating Li⊂[M]4 (M = Al, Ga) meso-metallaporphyrin and [Li(THF)4]+ cations. Density functional theory calculations determined that the weak Cl···H, H···H, N···H, and Cl···O interactions with a total interaction energy of -38.6 kcal·mol-1 are responsible for this unusual packing.

Synthesis of Cyclic and Cage Borosilicates Based on Boronic Acids and Acetoxysilylalkoxides. Experimental and Computational Studies of the Stability Difference of Six- and Eight-Membered Rings.

A series of borosilicates was synthesized, where the structure of the borosilicate core was easily modulated using two strategies: blocking of condensation sites and controlling the stoichiometry of the reaction. Thus, on the one hand, the condensation of phenylboronic or 3-hydroxyphenylboronic acid with diacetoxysilylalkoxide [(tBuO)(Ph3CO)Si(OAc)2] led to the formation of borosilicates (tBuO)(Ph3CO)Si{(µ-O)BPh}2(µ-O) (1), [{(tBuO)(Ph3CO)Si(µ-O)BPh(µ-O)}2] (2), and [{(tBuO)(Ph3CO)Si(µ-O)B(3-HOPh)(µ-O)}2] (3) with a cyclic inorganic B2SiO3 or B2Si2O4 core, respectively. On the other hand, the reaction of phenylboronic acid with triacetoxysilylalkoxide (Ph3CO)Si(OAc)3 in 3:2 ratio resulted in the formation of a cagelike structure [{(Ph3CO)Si(µ-O)2BPh(µ-O)}2] (4) with B4Si4O10 core, while the reaction of the boronic acid with silicon tetraacetate generated an unusual 1,3-bis(acetate)-1,3-diphenyldiboraxane PhB(µ-O)(µ-O,O'-OAc)2BPh (5). Additionally, compound 1 was used to evaluate the possibility to form N→B donor-acceptor bond between the boron atom in the borosilicates and a nitrogen donor. Thus, coordination of 1 with piperazine yielded a tricyclic [{(tBuO)(Ph3CO)Si(OBPh)2(µ-O)}2·C4H10N2] compound 6 with two borosilicate rings bridged by a piperazine molecule. Finally, the processes involved in the formation of the six- and eight-membered rings (B2SiO3 and B2Si2O4) in compounds 1 and 2 were explored using solution 1H NMR studies and density functional theory calculations. These molecules represent to the best of our knowledge first examples of cyclic molecular borosilicates containing SiO4 units.

Molecular Group 13 Metallaborates Derived from M-O-M Cleavage Promoted by BH3.

The reaction of metalloxanes [{MeLM(OH)}2(µ-O)] [M = Al (1), Ga (2); MeL = CH{CMe(NAr)}2-, Ar = 2,4,6-Me3C6H2, Me = methyl] with an excess of BH3·D (D = tetrahydrofuran (THF), SMe2) affords annular metallaborate systems achieved through M-O-M cleavage. Compound 1 led exclusively to the formation of eight-membered ring systems [{MeLAl(µ-O){B(OnBu)}(µ-O)}2] (3) and [{MeLAl(µ-O)(BH)(µ-O)}2] (6), while for 2 the unprecedented six-membered ring systems [{(MeLGa)2(µ-O)}(µ-O)2{B(OnBu)}] (4) and [(MeLGa)(µ-O)2{(BOnBu)2(µ-O)}] (5) were observed. The use of BH3·THF with 1 and 2 led to the concomitant THF ring-opening reaction, while with BH3·SMe2 in THF no such reaction was observed. The metallaborates [MeLAl{OB(pinacol)}(OH)] (7) and [{MeLGa(OB(pinacol))}2(µ-O)] (8) were synthesized from pinacolborane and the corresponding metalloxane, providing structural evidence that supports the reaction pathways proposed for the formation of 3-6. Density functional theory studies were performed on 3-5 to assess the effect of the metal exchange between aluminum and gallium atoms on the energy of the general ring structures.

Bottleneck Effect of N,N-Dimethylformamide in InOF-1: Increasing CO2 Capture in Porous Coordination Polymers.

The bottleneck effect of confined N,N-dimethylformamide (DMF) molecules was observed in InOF-1 for the first time: CO2 capture was remarkably enhanced in samples of as-synthesized InOF-1, thermally activated in such a way that a small residual amount of DMF molecules remained confined within the pores (DMF@InOF-1). Dynamic CO2 adsorption experiments on DMF@InOF-1 exhibited a CO2 capture of 8.06 wt % [1.5-fold higher than that of a fully activated InOF-1 (5.24%)]. DMF@InOF-1 can reversibly adsorb/desorb 8.09% CO2 with no loss of CO2 capacity after 10 cycles, and the desorption is accomplished by only turning the CO2 flow off. Static CO2 adsorption experiments (at 196 K) demonstrated a 1.4-fold CO2 capture increase (from 5.5 mmol·g-1, fully activated InOF-1, to 7.5 mmol·g-1, DMF@InOF-1). Therefore, these CO2 capture properties are the result of the presence of residual-confined DMF molecules within the InOF-1 framework and their interactions via a very strong hydrogen bond with the In2(µ-OH) groups, which prevent DMF leaching. The stability of this hydrogen bond is given by a perfect fit of the DMF molecule in the "dent" around the OH group that allows a nearly ideal orientation of the DMF molecule towards the OH group.

Molecular rare earth metal alumosilicates.

The synthesis and stabilization of molecular four-coordinated lanthanide alumosilicates was achieved by the use of a highly encumbered alumosilicate ligand LAl(OH·thf)(µ-O)Si(OH)(OtBu)2 (1, L = HC{C(Me)N(2,6-iPr2C6H3)}2). Reactions between 1 and tris-cyclopentadienyl lanthanides (LnCp3; Ln = Ce, Nd, Sm, Gd, Tb, Dy, Y, Er) derived in the isolation of eight compounds (2-9) where the ligand is observed in three different bonding modes: adducts (2, 3), spirocyclic (4) or cyclic (5-9) coordination compounds. The observed reactivity can be related to the ionic radius of the lanthanide atom and the nature of the oxygen donor-atom from the hydroxide (Al-OH) or hydroxyl (Si-OH) moieties in 1. Compounds 2-9 present general O-Al-O-Si-O-Ln connectivities with different degrees of substitution over the -OH groups in 1 and structural features with only slight variations over the alumosilicate moiety (O-Al-O-Si-O) upon the lanthanide coordination. The spirocyclic samarium derivative presents two tetra-coordinated samarium atoms with a tetrahedral and distorted square planar geometries, respectively, as a result of a highly strained polycyclic architecture.