Solvent-accessible Void Research Articles

Synthesis, crystal structure and NMR investigation of a new type of cyclic steroidal dimer based on brassinosteroids

A new type of cyclic steroidal dimer based on brassinosteroids has been synthesized via the reaction of 24-epibrassinolide with 1,4-phenylenediboronic acid and structurally characterized by single-crystal X-ray diffraction and 2D NMR analysis. The crystal structure of the dimer was found to contain rather large solvent accessible voids.

2-[Hydroxy(2-methoxyphenyl)methyl]acrylonitrile

In the title compound, C11H11NO2, the mean planes formed by the benzene ring and the C and N atoms of the acryl group are almost orthogonal to each other, with a dihedral angle of 85.7 (1)°. During the structure analysis, it was observed that the unit cell contains large accessible voids, with a volume of 186.9 Å3, which may host disordered solvent mol­ecules. This affects the diffraction pattern, mostly at low scattering angles. Density identified in these solvent-accessible areas was calculated and corrected for using the SQUEEZE routine in PLATON [Spek (2009 ▶), Acta Cryst. D65, 148–155]. Despite the presence of the hy­droxy group in the mol­ecule, no classical or nonclassical hydrogen bonds are observed in the structure. This may reflect the fact that the O—H group points towards the solvent-accessible void.

Octakis(dimethyl sulfoxide-κO)cerium(III) μ6-oxido-dodeca-μ2-oxido-hexaoxidohexamolybdate(VI) dimethyl sulfoxide tetrasolvate

The title complex, [Ce(C2H6OS)8]2[Mo6O19]3·4C2H6OS, was obtained as a byproduct of the reaction of [(C4H9)4N]2[Mo6O19] with Ce(NO3)3·6H2O and phthalic acid in dimethyl­sulfoxide solution. The asymmetric unit consists of a complex [Ce(C2H6OS)8]3+ cation, one and a half of the Lindqvist-type [Mo6O19]2− polyanions and two dimethyl­sulfoxide solvent mol­ecules; the half polyanion lies on an inversion center. The Ce3+ ion is coordinated by eight dimethyl­sulfoxide ligands through the O atoms in the form of a distorted square antiprism. The Ce—O bond lengths range from 2.429 (6) to 2.550 (5) Å. The cohesion of the structure is ensured by S⋯O [3.115 (6), 3.242 (10) and 3.12 (3) Å], O⋯O [3.037 (10) Å] and C—H⋯O inter­actions between cations and anions. The S and C atoms of a dmso ligand are disordered over three sites in a 0.45:0.30:0.25 ratio. The dimethyl­sulfoxide solvent mol­ecules are highly disordered and could not be modelled successfully; their contribution was therefore removed from the refinement using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]. Potential solvent-accessible voids of 500.0 Å3 occur in the crystal structure.

Oxido[N-(2-oxidobenzylidene-κO)leucinato-κ2N,O](1,10-phenanthroline-κ2N,N′)vanadium(IV)

In the title VIV complex, [VO(C13H15NO3)(C12H8N2)], the oxidovanadium cation is N,N′-chelated by a 1-10-phenanthroline ligand and N,O,O′-chelated by a Schiff base anion in a distorted octa­hedral geometry. Weak inter­molecular C—H⋯O hydrogen bonds occur in the crystal structure which contains solvent-accessible voids of 81 Å3.

Low-Dimensional Porous Coordination Polymers Based on 1,2-Bis(4-pyridyl)hydrazine: From Structure Diversity to Ultrahigh CO2/CH4 Selectivity

Solvothermal reactions of metal salts, benzenedicarboxylic acids, and 4,4'-azopyridine (azpy) in different conditions produced four coordination polymers, namely, [Zn(3)(bdc)(3)(bphy)(3)]·2DMF·10H(2)O (3; H(2)bdc = 1,4-benzenedicarboxylic acid, bphy = 1,2-bis(4-pyridyl)hydrazine, and DMF = N,N-dimethylformamide), [Ni(bdc)(bphy)]·DMF·3.5H(2)O (4), [Zn(nipa)(bphy)]·EtOH (5; H(2)nipa = 5-nitroisophthalic acid), and [CoBr(bdc)(0.5)(bphy)]·2DMA·H(2)O (6; DMA = N,N-dimethylacetamide), in which the azpy ligand was in situ reduced. Structural determination reveals that 3-5 consist of the same metal/ligand ratio and similar coordination modes, as well as similar two-dimensional square-grid networks, but differ from their packing/interpenetration modes. 3 consists of alternately arranged single layers and interweaved double layers. Single layers in 4 directly stack in an offset fashion, while 5 is constructed of interdigitated double layers. 6 is a one-dimensional ladderlike structure, which could be regarded as that half of the bridging benzenedicarboxylate ligands in 3-5 are replaced by monodentate bromide ions. Interestingly, the crystal structures of these low-dimensional coordination polymers contain considerable solvent-accessible voids. Thermogravimetric curves, powder X-ray diffraction, and gas sorption experiments were used to study the potential porosity of these structures, which indicated that they can all reversibly desorb and adsorb solvent molecules. In particular, 4 showed gated sorption behavior and high CO(2)/CH(4) selectivity because of its flexible structure.

Synthesis and structure determination of tetrakis(4-iodoanilinum) β-octamolybdate dihydrate

Tetrakis(4-iodoanilinum) β-octamolybdate dihydrate (I) was synthesized and its structure was solved using powder diffraction methods and the atoms positions optimized by the solid state DFT calculations. The structure is triclinic (P-1) with cell parameters: a=9.7099(4)Å, b=9.8169(3)Å, c=14.9842(6)Å, α=97.349(3)°, β=102.989(3)°, γ=113.335(3)°, V=1239.79Å3. The anion type was determined based on Patterson map analysis and the presence and location of water molecules were determined based on the locations of solvent accessible voids in the structure and confirmed with molecular dynamics calculations and high temperature IR spectroscopy.Structure of (I) consists of molybdenum–oxygen clusters, protonated amine and water molecules. Each cluster consists of eight distorted MoO6 octahedra sharing corners and edges forming β-[Mo8O26]4− anions. Protonated 4-iodoanilinum cations form, apart from electrostatic attraction, moderately strong NH⋯O hydrogen bonds binding these molecules to the oxygen atoms in Mo8O26 clusters. In addition, one of the amine molecules form a weak OH⋯I bond with the water molecule, which is loosely bound with a weak OH⋯O hydrogen bond to molybdenum–oxygen cluster.

Carboxylate-assisted acylamide metal–organic frameworks: synthesis, structure, thermostability and luminescence studies

We present a series of carboxylate-assisted ethylamide metal–organic frameworks, namely, Zn2(L)2(oba)2·2H2O(1, L = N1,N3-di(pyridin-3-yl)isophthalamide, H2oba = 4,4′-oxybis(benzoic acid)), Zn2(L)(nap)2·(DMF)2.5H2O(2, H2nap = 1,4-naphthalic acid, DMF = dimethylformamide), Cd(H2O)(L) (ip)·3H2O (3, H2ip = 1,3-benzenedicarboxylic acid), Cd(L)(ip)·2H2O(4). Polymer 1 crystallizes in the acentric Pca21 space group and presents an unprecedented topology prototype of noz-4-Pcca that allows three-fold interpenetration. Polymer 2 is a 3D supramolecular net with a considerable solvent-accessible void that is occupied by DMF and water molecules. As for polymers 3 and 4, the different formation of them is somewhat controlled by the concentration of initial materials such as 0.1 mmol Cd(NO3)2, L, ip in 8 mL water used for 3, 0.2 mmol Cd(NO3)2, L, ip in 8 mL water used for 4. In 3, a highly rare 1D porous ladder-type structure is observed, and further through hydrogen bonds a 2D supramolecular net is built. By contrast, a 3D α-Po net with two-fold interpenetration, based on a dinuclear Cd2(CO2)4 building block, is observed in 4. Moreover, their thermostability and luminescence properties are explored.

Synthesis, structural characterization and thermal properties of three copper(II) complexes based on aryl hydrazide ligands

The thiosemicarbazide and hydrazide Cu(II) complexes, [Cu3L21(py)4Cl2] (1), [Cu(HL2)py] (2) and [Cu(HL3)py] (3), (H2L1 = 1-picolinoylthiosemicarbazide, H3L2 = N′-(2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide, H3L3 = 2-hydroxy-N′-((2-hydroxy-naphthalen-1-yl)methylene)benzohydrazide) have been prepared and characterized through physicochemical and spectroscopic methods as well as X-ray crystallography. Complex 1 has a centrosymmetric structure with –N–N– bridged Cu3 skeleton. Neighboring molecules are linked into a 3D supermolecular framework by π–π stacking interactions, N–H···Cl and C–H···Cl hydrogen bonds. Complexes 2 and 3 have similar planar structures but different dimers formed by concomitant Cu···N and Cu···O interactions, respectively. Solvent accessible voids with a volume of 391 A3 are included in the structure of complex 2, indicating that this complex is a potential host candidate. Thermogravimetric analysis shows that the three complexes are stable up to 100 °C.

Di-μ-hydroxido-bis[tris(4,4,4-trifluoro-1-phenylacetylacetonato-κ2O,O′)hafnium(IV)] dimethylformamide disolvate

The binuclear molecule of the title compound, [Hf2(C10H6F3O2)6(OH)2]·2C3H7NO, lies across an inversion centre and contains a HfIV atom which is eight-coordinated and surrounded by three chelating β-diketonato tris­(4,4,4-trifluoro-1-phenyl­acetyl­acetonate (tfba−) ligands and two bridging OH− groups in a distorted square-anti­prismatic geometry. The Hf—O bond lengths vary from 2.073 (2) to 2.244 (2) Å and the O—Hf—O bite angles vary from 73.49 (9) to 75.60 (9)°. Weak O—H⋯O hydrogen-bonding inter­actions are observed between the bridging hy­droxy groups and the dimethylformamide solvent mol­ecules. The unit cell contains solvent-accessible voids of 131 Å3, but the residual electron density in the difference Fourier map suggests no solvent mol­ecule occupies this void.

Self-Assembly of Zr(C2O4)44– Metallotectons and Bisimidazolium Cations: Influence of the Dication on H-Bonded Framework Dimensionality and Material Potential Porosity

Assemblies involving [Zr(C2O4)4]4– metallotectons (C2O42– = oxalate) and linear, flexible, or V-shaped organic cations (H2-Lx)2+ derived from the 1,4-bisimidazol-1-ylbenzene molecule have been envisioned to elaborate porous frameworks based on ionic H-bonds. Five architectures of formula [{(H2-L1)2Zr(C2O4)4}·2H2O] (1), [{(H2-L2)2Zr(C2O4)4}·6H2O] (2), [{(H2-L3)2Zr(C2O4)4}·6H2O] (3), [{(H2-L4)2Zr(C2O4)4}·H2O] (4), and [{(H2-L5)2Zr(C2O4)4}·6H2O] (5) (with L1 = p-bis(imidazol-1-yl)benzene, L2 = p-bis(2-methylimidazol-1-yl)benzene, L3 = p-bis(imidazol-1-yl)-2,5-dimethylbenzene, L4 = p-bis(imidazol-1-ylmethyl)benzene, L5 = m-bis(imidazol-1-yl)benzene) have been obtained; 1–3, and 5 show an open-framework. For all, the bisimidazolium cations (H2-Lx)2+ act as bridges between anionic complexes. Depending on the chemical features of the cation, various assembling patterns have been observed, yielding one-dimensional (1D) (2, 5) two-dimensional (2D) (1), or three-dimensional (3D) (3, 4) H-bonded networks. While interconnection of anionic metallotectons and organic cations generally affords grids with large apertures, 2D and 3D H-bonded frameworks show the lowest potential porosities (and even compact architectures) because of interpenetration. Highest potential solvent accessible voids (up to 20%) are found for the 1D H-bonded assemblages because interpenetration does not occur for these materials. Crystal structures for all five architectures as well as their thermal stabilities are reported. Actual porosity has been evidenced for one of them by solving the structure of the guest free architecture.

Cubic assembly of a geometrically frustrated {Fe12} spin cluster

We describe an S(4)-symmetric {Fe(12)} spin cluster [Fe(12)O(4)(OH)(2)(L)(4)(OAc)(8)][Cl](2) {H(4)L = (HOCH(2)CH(2))(2)NCH(2)CH(2)N(CH(2)CH(2)OH)(2)} where the iron(III) centres describe a squashed hexagonal antiprism. The clusters pack into a large cubic cell with circular cavities, lined by weak C-H···O interactions, and a unit cell volume of over 60,000 Å(3) containing large solvent accessible voids. The core of the cluster is stable in solution, as confirmed by electrospray mass spectrometry. The cluster possesses a non-trivial, frustrated S = 0 ground state, due to the presence of multiple competing antiferromagnetic interactions. The finite temperature Lanczos method has been employed to calculate the temperature dependent magnetic properties of an analogous dodecanuclear S(i) = 3/2 model spin system, in order to reduce the very large Hilbert space. Three archetypal models with two independent exchange coupling parameters have been employed that render a low temperature feature possible, as seen in the χ vs. T plot for the {Fe(12)} spin cluster.

Driving the Assembling of Zirconium Tetraoxalate Metallotectons and Benzimidazolium Cations: From Three Dimensional Hydrogen-Bonded Compact Architectures to Open-Frameworks

Charge-assisted H-bond associations between [Zr(C2O4)4]4− preformed anionic complexes and several ditopic monocations based on the benzimidazolium motif ([H2-Bim]+ cations) have been envisioned for the tentative elaboration of 3D H-bonded and open-framework architectures. Reactions involving [Zr(C2O4)4]4− units and [H2-Bim]+ cations in (a) a charge stoichiometric amount, (b) a defect, and (c) an excess of cation afforded three different compounds of formula {(H2-Bim)4[Zr(C2O4)4]}·H2O (1), {K(H2O)(H2-Bim)3[Zr(C2O4)4]}·2H2O (2), and {(H2-Bim)4[Zr(C2O4)4]} (3), respectively. Structural analyses revealed marked differences in their formulations and in their supramolecular connectivities. These results traduce the importance of cation concentration on the association schemes. Among them, compound 3 exhibits a chiral structure analyzed as resulting from the interpenetration of two 3D H-bonded homochiral and independent networks. To avoid this interpenetration and to study the influence of the cation substitution for fixed experimental parameters, 2-amino and 2-methyl substituted [H2-Bim]+ cations ([H2-2-NH2Bim]+ and [H2-2-MeBim]+, respectively) have been envisioned as cationic building-blocks. Structure analysis for the corresponding materials ({(H2-2-NH2Bim)4[Zr(C2O4)4]} (4) and {(H2-2-MeBim)4[Zr(C2O4)4]}·7H2O (5), respectively) revealed that the amino group contributes in the H-bonded framework, whereas the methyl impairs the formation of H-bonds between the cations and the anions. These observations contribute to explain the marked structural differences between 3 and these two networks. With 5-methyl- and 5-chlorobenzimidazolium cations ([H2-5-MeBim]+ and [H2-5-ClBim]+, respectively), [Zr(C2O4)4]4− is converted into its binuclear version, [Zr2(C2O4)7]6−, yielding {(H2-5-MeBim)6[Zr2(C2O4)7]}·3H2O (6) with a close-packed 3D-network and {(H2-5-ClBim)6[Zr2(C2O4)7]}·13.5H2O (7) with an open-framework architecture (potential solvent accessible void volume of 23%). For 7, Cl···π interactions contribute to the cohesion of the 3D supramolecular architecture.

Guanidinium 2-phenylacetate

In the structure of the title salt, CH6N3 +·C8H7O2 −, the guanidinium cation gives three cyclic hydrogen-bonding inter­actions with O-atom acceptors of three independent phenyl­acetate anions, one R 2 2(8) and two R 2 1(6), giving one-dimensional columnar structures which extend down the 42 axis in the tetra­gonal cell. Within these structures, there are solvent-accessible voids of volume 86.5 Å3.

(2E,4E)-1-(6-Chloro-2-methyl-4-phenyl-3-quinolyl)-5-phenylpenta-2,4-dien-1-one

In the title compound, C27H20ClNO, the quinoline ring forms a dihedral angle of 62.53 (5)° with the substituent benzene ring. In the crystal, inter­molecular C—H⋯Cl inter­actions link the mol­ecules into chains along the b axis. Inter­molecular C—H⋯N and C—H⋯O hydrogen bonds further consolidate the structure into a three-dimensional network. The unit cell contains four solvent-accessible voids, each with a volume of 35 Å3, but no significant electron density was found in them.

Cis-Dichlorido(1,3-dimesitylimidazolidin-2-yl-idene)(2-formyl-benzyl-idene-κC,O)ruthenium diethyl ether solvate.

The title compound, [RuCl2(C8H6O)(C21H26N2)]·C4H10O, contains a catalytically active ruthenium carbene complex of the ‘second-generation Grubbs/Hoveyda’ type with Ru in a square-pyramidal coordination, the apex of which is formed by the benzyl­idene carbene atom with Ru=C 1.827 (2) Å. The complex shows the uncommon cis, rather than the usual trans, arrangement of the two chloride ligands, with Ru—Cl bond lengths of 2.3548 (6) and 2.3600 (6) Å, and a Cl—Ru—Cl angle of 89.76 (2)°. This cis configuration is desirable for certain applications of ring-opening metathesis polymerization (ROMP) of strained cyclic olefins. The crystalline solid is a diethyl ether solvate, which is built up from a porous framework of Ru complexes held together by π–π stacking and C—H⋯Cl and C—H⋯O inter­actions. The disordered diethyl ether solvent mol­ecules are contained in two independent infinite channels, which extend parallel to the c axis at x,y = 0,0 and x,y = , and have solvent-accessible void volumes of 695 and 464 Å3 per unit cell.

Nanoporous metal–organic framework comprising of 1D cobalt oxalate chains and flexible ligands exhibiting both dynamic gas adsorption and antiferromagnetic chain behaviours

A novel three-dimensional (3D) nanoporous metal–organic framework with moganite topology, [Co2(ox)2(dchtpy)]n·9nH2O (1·9H2O), has been obtained from the hydrothermal reaction of CoCl2, oxalic acid, NaOH and 1a,4a-dihydroxy-1e,2e,4e,5e-tetra(4-pyridyl)cyclohexane (dchtpy). X-ray analysis reveals that the bulky dchtpy ligands link four adjacent metal oxalate chains and form a 3D hybrid network with both moganite topology and 3D channels in various sizes. The largest pores (channel A) are the ones viewed along the a-axis, which are composed of two [Co(ox)]n chains and two bulky ligands in the dimensions of 10.76 × 10.67 A excluding the van der Waals radii. Along the {101} direction there was found the second large channels (channel B) in the size of 10.51 × 4.66 A. Notably the hydroxyl groups of dchtpy extend towards the channels on the middle of the walls, dividing the pores with two small channels in approximately 4.50 × 4.66 A. Besides, small pores in dimensions of 7.07 × 8.24 A and 6.98 × 6.06 A can also be found along the a- and c-axes, respectively. The potential solvent accessible void of the framework, calculated by PLATON, is 46.1% of the total volume and is occupied with disordered aqua molecules. Variable-temperature powder X-ray diffraction experiments confirmed that the crystallinity and network integrity of 1 can be retained up to 375 °C upon the removal of guest aqua molecules, in which thermal stability is among the most stable metal organic coordination frameworks. The framework shows guest-induced dynamic flexibility and elasticity and has a gating effect on the sorption of small gas molecules. The hydroxyl groups from the ligands functionalize the walls of the channels and have strong hydrogen bonds with adsorbents, leading to high sorption capacity at ambient temperature. Magnetic studies revealed significant antiferromagnetic interaction between the Co(II) ions in 1·9H2O with J = −12.4(1) cm−1 and g = 2.450(4).

Control of Channel Size for Selective Guest Inclusion with Inlaid Anionic Building Blocks in a Porous Cationic Metal–Organic Host Framework

Step by step: By attaching anionic building blocks of variable bulk to a cationic metal-organic framework, stepwise channel-size adjustment of the resulting porous three-dimensional host framework is achieved (see picture). This method is a new and viable approach for materials with predesigned nanopores for application in molecular recognition and selective guest inclusion.Through the introduction of perfluorocarboxylates as counteranions that line the inner surface of each channel in a host cationic metal-organic open framework, stepwise channel-size control has been realized, resulting in wide guest compatibility for [{Ag(L)(CF(3)CO(2))}(6)6 G](infinity) (1 supersetG; G=guest, L=ligand), selective guest recognition for [{Ag(L)(C(2)F(5)CO(2))}(6)4 G'](infinity) (2 supersetG'), and a lack of inclusion behavior for [{Ag(L)(C(3)F(7)CO(2))}(6)](infinity) (3; G and G' represent the same or different guest molecules). The cationic frameworks in 1-3 are constructed from the linkage of hexameric inorganic-organic hybrid macrocycles through multiple argentophilic interaction plus pi-pi interactions between pyridyl rings and carbonyl-carbonyl interactions, to which corresponding counteranions are attached. With different anions as intrachannel arms, similar frameworks in complexes 1 supersetG, 2 supersetG', and 3 exhibit percentages of guest-accessible voids of approximately 30-35, 25, and 18 % for 1-3, respectively. The highly flexible framework 1 in 1 supersetG contains stretchable channels with up to 21.7 % effective-volume change of the solvent-accessible void for inclusion of various guest species in the series of solvates 1 a-m. The pair of complexes 1 supersetG and [Ag(L)(CF(3)CO(2))](infinity) (4), and likewise the pair 2 supersetG' and [Ag(L)(C(2)F(5)CO(2))](infinity) (5), are interconvertible through distinct controllable processes.

Hydrogen bond directed open-framework of bis(bipyridine-glycoluril) phosphatocobalt(III) with solvent accessible void space

The self-assembled secondary building unit [Co(BPG)2(PO4)]·2H2O (1) with peripheral urea fused tectons having inherent hydrogen bond acceptor (O atoms) and donor (N–H atoms) groups results in a three-dimensional open-framework architecture with approximately 35% of solvent-accessible void space.

1-Bromo-2,4,6-tricyclohexylbenzene

The title compound, C24H25Br, packs efficiently in the crystal structure with no solvent-accessible voids and several inter­molecular H⋯H contacts approximating the sum of the van der Waals radii. The mol­ecule is quite crowded, with intra­molecular Br⋯H and C⋯H contacts ca 0.38 and 0.30 Å, respectively, less than the sum of the corresponding van der Waals radii. All cyclo­hexyl rings adopt chair conformations with the ‘seat’ of the chair inclined at approximately 57–81° to the mean plane of the benzene ring, while those ortho to bromine have their centroids displaced in opposite directions from this plane.

A Three-Dimensional Open-Framework Indium Selenide: [C7H10N][In9Se14

An open-framework indium selenide, [C7H10N][In9Se14], has been prepared under solvothermal conditions in the presence of 3,5-dimethylpyridine and characterized by single-crystal X-ray diffraction, thermogravimetry, elemental analysis, Fourier tranform IR spectroscopy, and UV-vis diffuse reflectance. The crystal structure of [C7H10N][In9Se14] contains an unusual building unit, in which corner- and edge-linked InSe45- tetrahedra coexist. The presence of one-dimensional circular channels, of ca. 6 A diameter, results in approximately 25% of solvent-accessible void space.