Ligand design for functional metal-organic frameworks.

Metal-organic frameworks (MOFs), also known as coordination polymers, are formed by the self-assembly of metallic centres and bridging organic linkers. In this critical review, we review the key advances in the field and discuss the relationship between the nature and structure of specifically designed organic linkers and the properties of the products. Practical examples demonstrate that the physical and chemical properties of the linkers play a decisive role in the properties of novel functional MOFs.

Chemistry and catalytic activity of molybdenum(VI)-pyrazolylpyridine complexes in olefin epoxidation. Crystal structures of monomeric dioxo, dioxo-μ-oxo, and oxodiperoxo derivatives.

The dioxomolybdenum(VI) complexes [MoO2Cl2(PzPy)] (1) and [MoO2(OSiPh3)2(PzPy)] (5) (PzPy = 2-[3(5)-pyrazolyl]pyridine) were synthesized and characterized by vibrational spectroscopy, with assignments being supported by DFT calculations. Complex 5 was additionally characterized by single crystal X-ray diffraction. Recrystallization of 1 under different conditions originated crystal structures containing either the mononuclear [MoO2Cl2(PzPy)] complex co-crystallized with 2-[3(5)-pyrazolyl]pyridinium chloride, binuclear [Mo2O4(μ2-O)Cl2(PzPy)2] complexes, or the oxodiperoxomolybdenum(VI) complex [MoO(O2)2Cl(PzPyH)], in which a 2-[3(5)-pyrazolyl]pyridinium cation weakly interacts with the Mo(VI) center via a pyrazolyl N-atom.

Microwave-assisted synthesis of metal-organic frameworks.

Microwave heating, used in organic chemistry for several decades, has only recently been applied to the preparation of multi-dimensional coordination polymers, more commonly known as metal-organic frameworks (MOFs). Microwave heating allows short reaction times, fast kinetics of crystal nucleation and growth, and high yields of desirable products which can be isolated with few or no secondary products. The most significant developments in the use of microwave heating for the preparation of MOFs are briefly reviewed from this perspective, emphasizing systematic studies of well-characterised materials, which lead to their isolation in large quantities over economically-viable periods of time.

Oxidation of volatile organic compounds on SBA-15 mesoporous molecular sieves modified with manganese.

Catalytic combustion of volatile organic compounds, such as propene, has been studied on manganese modified mesoporous molecular sieves. Powder X-ray diffraction, (29)Si nuclear magnetic resonance, nitrogen sorption and transmission electron microscopy show that the SBA-15 mesoporous silica molecular sieve can be modified with manganese using Mn(2)(CO)(10) or Mn(O(2)CMe)(2) without significant distortion of the host structure. The two products were catalytically active in propene oxidation, with SBA-15 modified with Mn(2)(CO)(10) showing significantly higher activity, possibly due to higher Mn content, than SBA-15 modified with Mn(O(2)CMe)(2).

Poly[[aqua-μ(3)-picolinato-μ(2)-picolinato-dipicolinatopotassium(I)terbium(III)] 2.5-hydrate].

In the title compound, [KTb(C(6)H(4)NO(2))(4)(H(2)O)]·2.5H(2)O, each Tb(3+) centre is coordinated by four N and five O atoms from five distinct picolinate ligands in a geometry resembling a highly distorted tricapped trigonal prism. One of the ligands establishes a skew bridge between neighbouring Tb(3+) centres, leading to the formation of one-dimensional anionic polymeric chains, {[(C(6)H(4)NO(2))(4)Tb](-)}(n), running along the direction [010].

Poly[[μ(2)-aqua-tetraaquahexakis(μ(4)-naph-thalene-2,6-dicarboxylato)tetra-holmium(III)] 1.75-hydrate].

In the title compound, {[Ho(4)(C(12)H(6)O(4))(6)(H(2)O)(5)]·1.75H(2)O}(n), which is isostructural with its Tb(3+)- and Eu(3+)-containing analogues, there are four crystallographically independent Ho(3+) centres, each exhibiting a highly distorted HoO(8) bicapped trigonal-prismatic coordination environment. Adjacent polyhedra are inter-connected via the carboxyl-ate groups and one μ(2)-bridging water mol-ecule, forming one-dimensional chains propagating along [100].

Microwave assisted synthesis of molybdenum and tungsten tetracarbonyl complexes with a pyrazolylpyridine ligand. Crystal structure of cis-[Mo(CO)4{ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate}].

We report the one-step syntheses in good yields of the complexes cis-[M(CO)4(pzpy)] {M = Mo, W; pzpy = ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate} directly from the corresponding M(CO)6 starting materials by using microwave-assisted heating and reaction times of either 30 s (M = Mo) or 15 min (M = W). The structure of the molybdenum tetracarbonyl complex was determined by single crystal X-ray diffraction. The compound is monomeric and the molybdenum atom has a highly distorted octahedral geometry.

Synthesis and structure of a sodium complex of an aromatic beta-diketone and pyrazolylpyridine.

Reaction of NaH with a THF solution of Eu(BTA)3(pypzH) [BTA = 1-benzoyl-3,3,3-trifluoroacetonate, pypzH = 2-(3-pyrazolyl)pyridine] leads to the formation of the europium-free tetrasodium complex [Na(4)(pypzH)(2)(micro4-BTA)(2)(micro2-BTA)(2)]. Single-crystal X-ray diffraction studies revealed the presence of a centrosymmetric Na+ hybrid tetramer,which fully occupies the contents of the triclinic unit cell. The crystal structure contains two individual Na+ cations, Na(1) and Na(2), which have highly irregular [NaN(2)O(3)] and[NaO(6)] local coordination environments, respectively.

A highly efficient dioxo(mu-oxo)molybdenum(VI) dimer catalyst for olefin epoxidation.

The oxo-bridged dimer [Mo(2)O(4)(mu(2)-O)Cl(2)(pzH)(4)] (1; pzH = pyrazole) exhibits unusually high activity in the liquid-phase catalytic epoxidation of the cyclic olefins cyclooctene and (R)-(+)-limonene under mild conditions and in the absence of additional organic solvents, using tert-butyl hydroperoxide as the oxidant. The complex is stable under the reaction conditions and can be used in further catalytic runs without significant loss of performance. An X-ray crystallographic investigation reveals that 1 has an unprecedented and extremely rare all-cis configuration at each of the MoO(2)-(mu(2)-O)Cl(pzH)(2) cores, which can be understood by considering supramolecular contacts and geometric factors.

Bis(tetra-methyl-amonium) bis-(2,4,5-carboxy-benzoate)-benzene-1,2,4,5-tetra-carboxylic acid (1/1).

The asymmetric unit of the title compound, 2C(4)H(12)N(+)·2C(10)H(5)O(8) (-)·C(10)H(6)O(8), consists of a tetra-methyl-amonium cation, an anion derived from the singly deprotonated pyromellitic acid anion, 2,4,5-carboxy-benzoate (H(3)bta(-)), and one-half of a benzene-1,2,4,5-tetra-carboxylic acid (H(4)bta) mol-ecule, which has the centroid of the aromatic ring positioned at a crystallographic centre of inversion. The H(4)bta and H(3)bta(-) residues are involved in an extensive inter-molecular O-H⋯O hydrogen-bonding network, which leads to a three-dimensional supra-molecular structure containing one-dimensional channels running parallel to the [001] crystallographic direction. These channels house the tetra-methyl-amonium cations.

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.

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.

Decaaqua-dioxidobis[μ(3)-N-(phospho-n-atometh-yl)imino-diacetato]-dizinc(II)-divanadium(IV) dihydrate.

The title compound, [Zn(2)V(2)(C(5)H(6)NO(7)P)(2)O(2)(H(2)O)(10)]·2H(2)O, contains a [V(2)O(2)(pmida)(2)](4-) dimeric anionic unit [where H(4)pmida is N-(phosphono-meth-yl)imino-diacetic acid] lying on a centre of symmetry which is exo-coordinated via the two deprotonated phospho-nate groups to two Zn(2+) cations, with the coordination environment of Zn completed by five water mol-ecules. The crystal packing is mediated by an extensive network of strong and highly directional O-H⋯O hydrogen bonds involving the water mol-ecules (coordinated and uncoordinated) and the functional groups of pmida(4-), leading to a three-dimensional supra-molecular network.

Poly[hexa-aqua-bis(μ(3)-naphthalene-2,6-dicarboxyl-ato)(μ(2)-naphthalene-2,6-dicarboxyl-ato)diholmium(III)].

The crystal structure of the title compound, [Ho(2)(C(12)H(6)O(4))(3)(H(2)O)(6)](n), contains binuclear centrosymmetric {Ho(2)O(2)(CO(2))(4)(H(2)O)(6)} cores inter-connected via the naphthalene-2,6-dicarboxyl-ate (NDC(2-)) bridging ligands into a two-dimensional neutral plane net, ∞(2)[Ho(2)(NDC)(3)(H(2)O)(6)], exhibiting a typical (4,4)-topology. Inter-actions between adjacent layers are assured by a series of C-H⋯π contacts and a number of strong and highly directional O-H⋯O hydrogen bonds involving the coordinated water mol-ecules and neighbouring coordinated carboxyl-ate groups. One NDC(2-) bridging ligand has its centroid located at a crystallographic centre of inversion.

Simulating self-assembly of ZnS nanoparticles into mesoporous materials.

Characterization of materials is crucial for the quantification and prediction of their physical, chemical, and mechanical properties. However, as the complexity of a system increases, so do the challenges involved in elucidating its structure. While molecular simulation and modeling have proved invaluable as complements to experiment, such simulations now face serious challenges: new materials are being synthesized with ever increasing structural complexity, and it may soon prove impossible to generate models that are sufficiently realistic to describe them adequately.

One-dimensional silver(I) chain of lacunary alpha-Keggin anions.

A novel chain-like silver polyoxotungstophosphate is formed when Ag(I) metal centres, exhibiting an unusual eight-coordination fashion, bridge a monolacunary [PW11O39]7- anion to four bridging mu2-oxygen atoms of a neighbouring lacunary alpha-Keggin anion.

X-ray diffraction and solid-state NMR studies of a germanium binuclear complex.

A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2] x 4 H2O (where pmida(4-) = N-(phosphonomethyl)iminodiacetate and C4H12N2(2+) = piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids.

Hypothetical binodal zeolitic frameworks.

Hypothetical binodal zeolitic structures (structures containing two kinds of tetrahedral sites) were systematically enumerated using tiling theory and characterized by computational chemistry methods. Each of the 109 refineable topologies based on "simple tilings" was converted into a silica polymorph and its energy minimized using the GULP program with the Sanders-Catlow silica potential. Optimized structural parameters, framework energies relative to alpha-quartz and volumes accessible to sorption have been calculated.

Novel cerium(IV) heteropolyoxotungstate containing two types of lacunary Keggin anions.

A novel V-shaped polyoxotungstate is formed when Ce(IV) metal centres bridge monolacunary [PW(11)O(39)](7-) anions to an unusual 1,4-bilacunary [PW(10)O(38)](11-) anion which appears with an unprecedented bridging structural motif.

Photoluminescent layered lanthanide silicates.

The hydrothermal synthesis and structural characterization of layered lanthanide silicates, K(3)[M(1-a)Ln(a)Si(3)O(8)(OH)(2)] (M = Y(3+), Tb(3+); Ln = Eu(3+), Er(3+), Tb(3+), and Gd(3+)), named AV-22 materials, are reported. The structure of these solids was elucidated by single-crystal (180 K) and powder X-ray diffraction and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, (29)Si MAS NMR, and photoluminescence spectroscopy. The Er-AV-22 material is a room-temperature infrared phosphor, while Tb- and Eu-AV-22 are visible emitters with output efficiencies comparable to standards used in commercial lamps.

Chemical evaluation of hypothetical uninodal zeolites.

Optimized structural parameters, framework energies relative to alpha-quartz, and volumes accessible to sorption have been calculated for the systematically enumerated hypothetical uninodal zeolitic structures (structures in which all tetrahedral sites are equivalent). The structures were treated as silica polymorphs, and their energies were minimized using the GULP program with the Sanders-Catlow silica potential. Results are given for 164 structures, which include all 21 known uninodal zeolites, two known minerals (tridymite and cristobalite), and 78 unknown zeolite topologies.

Synthesis and characterization of a novel cadmium-organic framework with trimesic acid and 1,2-bis(4-pyridyl)ethane.

The hydrothermal reaction between Cd(NO(3))(2), trimesic acid (H(3)BTC), 1,2-bis(4-pyridyl)ethane (BPE), and triethylamine under mild conditions yielded, after 3 days, a novel three-dimensional metal-organic framework, [Cd(1.5)(BTC)(BPE)(H(2)O)(2)].(H(2)O), which has been characterized structurally using single-crystal and powder X-ray diffraction, elemental analysis, infrared and Raman spectroscopies, thermogravimetry, and differential scanning calorimetry.

Two- and three-dimensional cadmium-organic frameworks with trimesic acid and 4,4'-trimethylenedipyridine.

Three novel cadmium-organic frameworks built-up from 1,3,5-benzenetricarboxylate anions (HXBTC(x-3)) and 4,4'-trimethylenedipyridine (TMD) have been hydrothermally synthesized, and characterized using single-crystal X-ray diffraction, thermoanalytical measurements, elemental analysis, and IR and Raman spectroscopies: [Cd(HBTC)(TMD)(2)].8.5H(2)O (I), [Cd(HBTC)(TMD)(H(2)O)].