A Copper(I)-Thioarsenate(III) Inorganic Framework Directed by [Ni(en)3]2.

One novel three-dimensional (3-D) copper(I)-thioarsenate(III) [Ni(en)3]Cu4As4S9 (1, en = ethylenediamine) has been solvothermally prepared with the utilization of the in situ formation of [Ni(en)3]2+ complex as structure-directing agent (SDA). 1 contains cubane-like [Cu8S12]16- clusters and rare tetrameric [As4S9]6- units, which are interconnected to generate the first example of a 3-D anionic framework [Cu4As4S9]n2n-, topologically identical to pyrite, and having large channels filled by [Ni(en)3]2+ complex cations. 1 is a potential wide-band-gap semiconductor with an energy gap of 1.91 eV that exhibits selectively photocatalytic degradation of methylene blue under visible-light irradiation. The density functional theory calculation, photocurrent response, and magnetic properties of 1 were also investigated.

Vanadoborates: cluster-based architectures, preparation and properties.

Crystalline polyoxovanadates (POVs) are a subclass of polyoxometalates with significance in chemical, physical and materials sciences. Recent studies revealed that the condensation of vanadate and borate fragments may yield a whole new class of POVs. These novel vanadoborates are typically prepared by high-temperature solid-state, boric acid flux or low-temperature hydrothermal techniques. The different connections of [VOx] (x = 4, 5, 6) and [BOx] (x = 3, 4) polyhedral units ultimately result in a fascinating variety of vanadoborate anionic clusters, which can be at the genesis of a myriad of one-dimensional (1-D), two-dimensional (2-D) and three-dimensional (3-D) polymeric architectures by way of either self-condensation or by forming covalent bonds with other metal ions or unsaturated metal complexes. This review summarizes, in a systematic structural approach, the most striking advances in the syntheses, structural features, and some properties of crystalline vanadoborates based on different [VxBy] and [VxByPz] clusters. It intends to provide meaningful and helpful guidance for the future preparation of new and functional vanadoborates.

Crystal structure of an organic-inorganic supra-molecular salt based on a 4,4'-methyl-enebis(3,5-dimethyl-1H-pyrazol-2-ium) cation and a ß-octa-molybdate anion.

The asymmetric unit of the title compound, bis-[4,4'-methyl-enebis(3,5-dimethyl-1H-pyrazol-2-ium)] ß-octa-molybdate, (C11H18N4)2[Mo8O26] or (H4mbdpz)2[Mo8O26], is composed of an H4mbdpz(2+) cation and half of the ß-octa-molybdate anion which is completed by inversion symmetry. The organic mol-ecular units are engaged in a series of N-H⋯O hydrogen bonds with neighbouring anions, with N⋯O distances and N-H⋯O angles in the ranges 2.730 (2)-2.941 (2) Šand 122-166°, respectively. These inter-actions lead to the formation of a supra-molecular two-dimensional network parallel to the (010) plane.

Crystal Structure and Catalytic Behavior in Olefin Epoxidation of a One-Dimensional Tungsten Oxide/Bipyridine Hybrid.

The tungsten oxide/2,2'-bipyridine hybrid material [WO3(2,2'-bpy)]·nH2O (n = 1-2) (1) has been prepared in near quantitative yield by the reaction of H2WO4, 2,2'-bpy, and H2O in the mole ratio of ca. 1:2:700 at 160 °C for 98 h in a rotating Teflon-lined digestion bomb. The solid-state structure of 1 was solved and refined through Rietveld analysis of high-resolution synchrotron X-ray diffraction data collected for the microcrystalline powder. The material, crystallizing in the orthorhombic space group Iba2, is composed of a one-dimensional organic-inorganic hybrid polymer, ∞(1)[WO3(2,2'-bpy)], topologically identical to that found in the previously reported anhydrous phases [MO3(2,2'-bpy)] (M = Mo, W). While in the latter the N,N'-chelated 2,2'-bpy ligands of adjacent corner-shared {MO4N2} octahedra are positioned on the same side of the 1D chain, in 1 the 2,2'-bpy ligands alternate above and below the chain. The catalytic behavior of compound 1 for the epoxidation of cis-cyclooctene was compared with that for several other tungsten- or molybdenum-based (pre)catalysts, including the hybrid polymer [MoO3(2,2'-bpy)]. While the latter exhibits superior performance when tert-butyl hydroperoxide (TBHP) is used as the oxidant, compound 1 is superior when aqueous hydrogen peroxide is used, allowing near-quantitative conversion of the olefin to the epoxide. With H2O2, compounds 1 and [MoO3(2,2'-bpy)] act as sources of soluble active species, namely, the oxodiperoxo complex [MO(O2)2(2,2'-bpy)], which is formed in situ. Compounds 1 and [WO(O2)2(2,2'-bpy)] (2) were further tested in the epoxidation of cyclododecene, trans-2-octene, 1-octene, (R)-limonene, and styrene. The structure of 2 was determined by single-crystal X-ray diffraction and found to be isotypical with the molybdenum analogue.

Redetermination of the crystal structure of 3,5-di-methyl-pyrazolium ß-octa-molybdate tetra-hydrate.

The title compound, (C5H9N2)4[Mo8O26]·4H2O, was reported previously from a room-temperature data collection from which only the metal atoms could be refined anisotropically [FitzRoy et al. (1989 ▸). Inorg. Chim. Acta, 157, 187-194]. The current redetermination at 180 (2) K models all the non-H atoms with anisotropic displacement parameters and fully describes the supra-molecular N-H⋯O and O-H⋯O hydrogen-bonded network connecting the 3,5-di-methyl-pyrazolium cations, the water mol-ecules of crystallization and the ß-octa-molybdate anion. All H atoms involved in the three-dimensional hydrogen-bonding network could be located from difference Fourier maps, with the exception of those of one disordered water mol-ecule, firstly seen in this structural report [refined over two distinct locations with site-occupancy factors of 0.65 (2) and 0.35 (2)]. The complete ß-octa-molybdate anion is generated by a crystallographic inversion centre.

Synthesis, structural elucidation, and catalytic properties in olefin epoxidation of the polymeric hybrid material [Mo3O9(2-[3(5)-pyrazolyl]pyridine)]n.

The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)]n (2) as a microcrystalline powder in yields of 72­79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)2(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl4(2­) anion, and the tetranuclear compound [Mo4O12(pzpy)4] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O2)2(pzpy)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic­inorganic one-dimensional (1D) polymer, ∞(1)[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction.

Investigation of a dichlorodioxomolybdenum(VI)-pyrazolylpyridine complex and a hybrid derivative as catalysts in olefin epoxidation.

Treatment of the solvent adduct [MoO(2)Cl(2)(THF)(2)] with the ligand 2-(1-pentyl-3-pyrazolyl)pyridine (1, abbreviated as pent-pp) gave the dioxomolybdenum(VI) complex [MoO(2)Cl(2)(pent-pp)] (2), which was characterised by elemental analysis, (1)H NMR, FT-IR spectroscopy and single crystal X-ray diffraction (XRD). Reaction of 2 with water in a Teflon-lined stainless steel autoclave at 100 °C led to the isolation of a molybdenum oxide/pyrazolylpyridine hybrid material with the composition [Mo(2)O(6)(pent-pp)] (3), which was characterised by variable temperature powder XRD, scanning electron microscopy, thermogravimetric analysis, FT-IR and (13)C{(1)H} CP MAS NMR spectroscopies. Compounds 2 and 3 display high activity and selectivity when used as (pre)catalysts for the epoxidation of cis-cyclooctene at 55 °C with tert-butylhydroperoxide as an oxidant. Further catalytic experiments with 3 as a (pre)catalyst were performed using the bio-derived olefins DL-limonene (Lim) and methyl oleate (Ole). The reaction of Lim gave mainly 1,2-epoxy-p-menth-8-ene and 1,2;8,9-diepoxy-p-menthane in a combined yield of 93% at 97% conversion (6 h), while the reaction of Ole led to 9,10-epoxystearate as the main product in 78% yield at 82% conversion (6 h). The catalytic reactions are homogeneous in nature. Starting with material 3, the oxodiperoxo complex [MoO(O(2))(2)(pent-pp)] (4) was isolated from solution after a catalytic run, suggesting that it is formed from 3 and plays a catalytic role.

Hydrothermal synthesis, crystal structure, and catalytic potential of a one-dimensional molybdenum oxide/bipyridinedicarboxylate hybrid.

The reaction of MoO3, 2,2'-bipyridine-5,5-dicarboxylic acid (H2bpdc), water, and dimethylformamide in the mole ratio 1:1:1730:130 at 150 °C for 3 days in a rotating Teflon-lined digestion bomb leads to the isolation of the molybdenum oxide/bipyridinedicarboxylate hybrid material (DMA)[MoO3(Hbpdc)]·nH2O (1) (DMA = dimethylammonium). Compound 1 was characterized by scanning electron microscopy, FT-IR and (13)C{(1)H} CP MAS NMR spectroscopies, and elemental and thermogravimetric analyses. The solid state structure of 1 was solved and refined through Rietveld analysis of high resolution synchrotron X-ray powder diffraction data in conjunction with information derived from the above techniques. The material, crystallizing in the noncentrosymmetric monoclinic space group Pc, is composed of an anionic one-dimensional organic-inorganic hybrid polymer, ∞(1)[MoO3(Hbpdc)](-), formed by corner-sharing distorted {MoO4N2} octahedra, which cocrystallizes with charge-balancing DMA(+) cations and one water molecule per metal center. In the crystal structure of 1, the close packing of individual anionic polymers, DMA(+) cations, and water molecules is mediated by a series of supramolecular contacts, namely strong (O-H···O, N(+)-H···O(-)) and weak (C-H···O) hydrogen bonding interactions, and π-π contacts involving adjacent coordinated Hbpdc(-) ligands. The catalytic potential of 1 was investigated in the epoxidation reactions of the bioderived olefins methyl oleate (Ole) and DL-limonene (Lim) using tert-butylhydroperoxide (TBHP) as the oxygen donor and 1,2-dichloroethane (DCE) or (trifluoromethyl)benzene (BTF) as cosolvent, at 55 or 75 °C. Under these conditions, 1 acts as a source of active soluble species, leading to epoxide yields of up to 98% for methyl 9,10-epoxystearate (BTF, 75 °C, 100% conversion of Ole) and 89% for 1,2-epoxy-p-menth-8-ene (DCE, 55 °C, 95% conversion of Lim). Catalytic systems employing the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as solvent could be effectively recycled.

Synthesis, structural elucidation, and application of a pyrazolylpyridine-molybdenum oxide composite as a heterogeneous catalyst for olefin epoxidation.

The reaction of [MoO(2)Cl(2)(pypzEA)] (1) (pypzEA = ethyl[3-(pyridin-2-yl)-1H-pyrazol-1-yl]acetate) with water in a Teflon-lined stainless steel autoclave (100 °C) or in an open reflux system leads to the isolation of the molybdenum oxide/pyrazolylpyridine composite material [Mo(2)O(6)(HpypzA)] (2; HpypzA = [3-(pyridinium-2-yl)-1H-pyrazol-1-yl]acetate). The solid state structure of 2 was solved through single crystal and powder X-ray diffraction analyses in conjunction with information derived from FT-IR and (13)C CP MAS NMR spectroscopies and elemental analyses. In the asymmetric unit of 2, two crystallographically distinct Mo(6+) centers are bridged by a syn,syn-carboxylate group of HpypzA. The periodic repetition of these units along the a axis of the unit cell leads to the formation of a one-dimensional composite polymer, (∞)(1)[Mo(2)O(6)(HpypzA)]. The outstretched pyrazolylpyridine groups of adjacent polymers interdigitate to form a zipper-like motif, generating strong onset π-π contacts between adjacent rings of coordinated HpypzA molecules. The composite oxide 2 is a stable heterogeneous catalyst for liquid-phase olefin epoxidation.

An octanuclear molybdenum(VI) complex containing coordinatively bound 4,4'-di-tert-butyl-2,2'-bipyridine, [Mo8O22(OH)4(di-tBu-bipy)4]: synthesis, structure, and catalytic epoxidation of bio-derived olefins.

The reaction of [MoO(2)Cl(2)(di-tBu-bipy)] (1) (di-tBu-bipy = 4,4'-di-tert-butyl-2,2'-bipyridine) with water at 100-120 °C in a Teflon-lined stainless steel autoclave, in an open reflux system, or in a microwave synthesis system gave the octanuclear complex [Mo(8)O(22)(OH)(4)(di-tBu-bipy)(4)] (2) as a microcrystalline powder in good yields. Single crystals of 2 suitable for X-ray diffraction were obtained by the reaction of MoO(3) and di-tBu-bipy in water at 160 °C for 3 days. The molecular structure of 2 comprises a purely inorganic core, Mo(4)O(8)(µ(3)-OH)(2)(µ(2)-O)(2), attached to two peripheral oxo-bridged binuclear units, Mo(2)O(4)(µ(2)-O)(2)(OH)(di-tBu-bipy)(2). The inorganic core is composed of a unique assembly of four {MoO(5)} distorted square pyramids connected to each other via edge-sharing. Overall, the octanuclear complex adopts a highly distorted form strongly resembling an "S"-shaped molecular unit. Complex 2 was applied in the catalytic epoxidation of the biorenewable olefins DL-limonene (Lim) and methyl oleate (Ole), using tert-butylhydroperoxide (TBHP) as an oxygen donor, under mild reaction conditions (55 °C, air). The reactions of Lim and Ole gave the respective epoxide monomers in fairly high selectivities at high conversions (89% 1,2-epoxy-p-menth-8-ene selectivity at 96% Lim conversion; 99% methyl 9,10-epoxystearate selectivity at 94% Ole conversion, reached within 24 h reaction). Iodometric titrations revealed no measurable "non-productive" decomposition of TBHP.

Tris(4,4'-di-tert-butyl-2,2'-bipyridine-κN,N')molybdenum(II) µ(6)-oxido-dodeca-µ(2)-oxido-hexa-oxidohexa-molybdate(VI) acetonitrile tetra-solvate.

The asymmetric unit of the title compound, [Mo(C(18)H(24)N(2))(3)][Mo(6)O(19)]·4CH(3)CN, comprises an [Mo(di-t-Bu-bipy)(3)](2+) cation (di-t-Bu-bipy is 4,4'-di-tert-butyl-2,2'-bipyridine), two halves of Lindqvist-type [Mo(6)O(19)](2-) anions (with each anion completed by the application of a center of inversion) and four acetonitrile solvent mol-ecules. The geometry around the metal atom of the cation resembles a distorted octa-hedron, with each of the three di-t-Bu-bipy ligands being almost planar [deviation from planarity < 6.3 (2)°]. Supra-molecular inter-actions, namely Mo=O⋯π, C N⋯π, C-H⋯O and C-H⋯N, along with electrostatic forces, mediate the crystal packing. Two of the tert-butyl groups are affected by rotational disorder which was modeled over two distinct positions with major site occupancies of 0.707 (9) and 0.769 (8).

4,4'-Di-tert-butyl-2,2'-dipyridinium dichloride.

In the title compound, C(18)H(26)N(2) (2+)·2Cl(-), the complete dication is generated by crystallographic inversion symmetry; both N atoms are protonated and engaged in strong and highly directional N-H⋯Cl hydrogen bonds. Additional weak C-H⋯Cl contacts promote the formation of a tape along ca. [110]. The crystal structure can be described by the parallel packing of these tapes. The crystal studied was a non-merohedral twin with twin law [-1 0 0, 0 -1 0, -0.887 0.179 1] and the final BASF parameter refining to 0.026 (2) .

Synthesis, structure, and catalytic performance in cyclooctene epoxidation of a molybdenum oxide/bipyridine hybrid material: {[MoO3(bipy)][MoO3(H2O)]}n.

The reaction of [MoO(2)Cl(2)(bipy)] (1) (bipy = 2,2'-bipyridine) with water in a Teflon-lined stainless steel autoclave (100 degrees C, 19 h), in an open reflux system with oil bath heating (12 h) or in a microwave synthesis system (120 degrees C, 4 h), gave the molybdenum oxide/bipyridine hybrid material {[MoO(3)(bipy)][MoO(3)(H(2)O)]}(n) (2) as a microcrystalline powder in yields of 72-92%. The crystal structure of 2 determined from synchrotron X-ray powder diffraction data is composed of two distinct neutral one-dimensional polymers: an organic-inorganic polymer, [MoO(3)(bipy)](n), and a purely inorganic chain, [MoO(3)(H(2)O)](n), which are interconnected by O-H...O hydrogen bonding interactions. Compound 2 is a moderately active, stable, and selective catalyst for the epoxidation of cis-cyclooctene at 55 degrees C with tert-butylhydroperoxide (tBuOOH, 5.5 M in decane or 70% aqueous) as the oxidant. Biphasic solid-liquid or triphasic solid-organic-aqueous mixtures are formed, and 1,2-epoxycyclooctane is the only reaction product. When n-hexane is employed as a cosolvent and tBuOOH(decane) is the oxidant, the catalytic reaction is heterogeneous in nature, and the solid catalyst can be recycled and reused without a loss of activity. For comparison, the catalytic performance of the precursor 1 was also investigated. The IR spectra of solids recovered after catalysis indicate that 1 transforms into the organic-inorganic polymer [MoO(3)(bipy)] when the oxidant is tBuOOH(decane) and compound 2 when the oxidant is 70% aqueous tBuOOH.

Heterometallic complexes involving iron(II) and rhenium(VII) centers connected by mu-oxido bridges.

The reaction of FeI(2) with two equivalents of AgReO(4) in acetonitrile leads to yellow, crystalline Fe(ReO(4))(2)(CH(3)CN)(3) (1), and the treatment of 1 with four equivalents of CpFe(CO)(2)CN gives orange, crystalline Fe(ReO(4))(2)[CpFe(CO)(2)(CN)](4) (2). Compound 2 can also be prepared in one step by the reaction of FeI(2), AgReO(4) and CpFe(CO)(2)CN in dichloromethane. The structure of 1 consists of infinite chains in which alternating {Fe(CH(3)CN)(4)} and {Fe(ReO(4))(2)(CH(3)CN)(2)} units are linked by perrhenate anions to form a (-ReO(2)-O-Fe(ReO(4))(2)(CH(3)CN)(2)-O-ReO(2)-O-Fe(CH(3)CN)(4)-O-)(n) molecular wire. The structure of 2 shows a monomeric iron complex with a slightly distorted octahedral coordination environment consisting of four organometallic complexes coordinated in the equatorial plane via the cyanide groups and two monodentate perrhenates in the corresponding apical positions. Both compounds were further characterised in the solid state by IR spectroscopy, thermogravimetric analysis and magnetic susceptibility measurements. The magnetic data indicate that 1 behaves as a ferrimagnetic chain with 3D ordering below 8 K due to inter-chain interactions. Compound 2 has antiferromagnetic interactions within the Fe(ReO(4))(2)[CpFe(CO)(2)(CN)](4) clusters.

Microwave-assisted synthesis and crystal structure of oxo(diperoxo)(4,4'-di-tert-butyl-2,2'-bipyridine)-molybdenum(VI).

The oxodiperoxo complex MoO(O2)(2)(tbbpy) (tbbpy = 4,4'-di-tert-butyl-2,2'- bipyridine) was isolated from the reaction of MoO2Cl(2)(tbbpy) in water under microwaveassisted heating at 120 masculineC for 4 h. The structure of the oxodiperoxo complex was determined by single crystal X-ray diffraction. The Mo(VI) centre is seven-coordinated with a geometry which strongly resembles a highly distorted bipyramid. Individual MoO(O2)(2)(tbbpy) complexes are interdigitated along the [010] direction to form a column. The crystal structure is formed by the close packing of the columnar-stacked complexes. Interactions between neighbouring columns are essentially of van der Waals type mediated by the need to effectively fill the available space.

Mo(4)(eta(3)-allyl)(4)Cl(2)(OH)(2)(CO)(8): the first cubane-type Mo(2+) organometallic complex with mu(3)-OH and mu(3)-Cl bridges.

The reaction between fluorenyllithium and Mo(eta(3)-C(3)H(5))Cl(NCMe)(2)(CO)(2) led to the isolation of di-mu(3)-chlorido-di-mu(3)-hydroxido-tetrakis[(eta(3)-allyl)dicarbonylmolybdenum(II)]-9-fluorenone-tetrahydrofuran (1/1/1), [Mo(4)(C(3)H(5))(4)Cl(2)(OH)(2)(CO)(8)].C(4)H(8)O.C(13)H(8)O. The tetrametallic Mo(4) unit constitutes the first example of a complex containing simultaneously two mu(3)-OH groups and two mu(3)-Cl anions capping the metallic trigonal prism. The four crystallographically independent Mo(2+) centres exhibit distorted octahedral geometry with the eta(3)-allyl groups being trans-coordinated to a mu(3)-OH group and the carbonyl groups occupying the equatorial plane. Space-filling tetrahydrofuran and 9-fluorenone molecules are engaged in strong O-H...O hydrogen-bonding interactions with Mo(4)(eta(3)-allyl)(4)Cl(2)(OH)(2)(CO)(8) complexes.

2-(1H-Pyrazol-3-yl)pyridinium chloride monohydrate.

The title organic salt, C(8)H(8)N(3) (+)·Cl(-)·H(2)O, exhibits a rich hydrogen-bonding network involving all constituent species. The water mol-ecules are engaged in strong O-H⋯Cl inter-actions with the chloride anions, two neighboring protonated 2-(1H-pyrazol-3-yl)pyridinium species inter-act via N-H⋯N bonds with two pyrazole rings. Further, a short and highly directional C-H⋯O inter-action is observed connecting the pyridinium ring to the water mol-ecule of crystallization. Weak C-H⋯Cl and N-H⋯Cl inter-actions contribute to the stabilization of the crystal structure.

4,4'-Di-tert-butyl-2,2'-bipyridine.

In the title compound, C(18)H(24)N(2), the mol-ecular unit adopts a trans conformation around the central C-C bond [N-C-C-N torsion angle of 179.2 (3)°], with the two aromatic rings almost coplanar [dihedral angle of only 0.70 (4)°]. The crystal packing is driven by co-operative contacts involving weak C-H⋯N and C-H⋯π inter-actions, and also the need to fill effectively the available space.

1-Hydr-oxy-1,1,3,3,3-penta-phenyl-disiloxane, [Si(2)O(OH)(Ph)(5)], at 100 K.

In the crystal structure of the title compound, C(30)H(26)O(2)Si(2), one Si(Ph)(3) residue is bound to another Si(OH)(Ph)(2) residue via a non-linear Si-O-Si bridge. The asymmetric unit is composed of two such molecules which inter-act, on the one hand, via a strong and highly directional O-H⋯O hydrogen bond involving the two neighbouring Si-OH units and, on the other, via an O-H⋯π contact connecting the second hydroxyl group with an adjacent phenyl group.

1-Hydr-oxy-1,1,3,3,3-penta-phenyl-disiloxane, [Si(2)O(OH)(Ph)(5)], at 150 K.

In the crystal structure of the title compound, C(30)H(26)O(2)Si(2), one Si(Ph)(3) residue is bound to another Si(OH)(Ph)(2) residue via a nonlinear Si-O-Si bridge. The asymmetric unit is composed of four [Si(2)O(OH)(Ph)(5)] molecules. Each pair of adjacent molecules inter-acts via strong and highly directional O-H⋯O hydrogen bonds connecting neighbouring Si-OH units, and via inter-unit O-H⋯π contacts connecting the second hydroxyl groups with adjacent phenyl groups.