Luminescent and magnetic [TbEu] 2D metal-organic frameworks.

We present the synthesis, through a simple, microwave-assisted method, of lanthanoid-based 2D metal-organic frameworks (MOFs) of general formula [LnxLn'1-x(MeCOO)(PhCOO)2], including homonuclear compounds (x = 1), LnEu, Tb, and heterometallic compounds, [TbEu]. The crystalline material is formed by neutral nanosheets held together by van der Waals interactions, which can be easily exfoliated by sonication. Photoluminescent emission in the visible range was observed for all of the synthesized 2D MOF compounds via excitation of the ligand, showing benzoates are efficient antenna ligands. Efficient energy transfer from Tb → Eu was observed in the heterometallic [TbEu] compounds, which could potentially perform as luminescent thermometers. Inks containing nanosheets of 2D MOFs exfoliated in solution were prepared, and luminescent prints of Tb and Eu 2D MOFs on paper were made to show the possible application for anticounterfeiting. Frequency-dependent ac susceptibility results show the occurrence of slow magnetic relaxation in [TbEu] compounds through direct relaxation mechanisms, affected by bottleneck effect. A slowing down of the relaxation time is observed as the Eu/Tb ratio increases.

Microwave assisted synthesis of heterometallic 3d-4f M4Ln complexes.

In this paper we describe the synthesis and magnetic properties of a series of 3d-4f complexes of general formula [M4Ln(OH)2(chp)4(SALOH)5(H2O)(MeCN)(Solv)] (Solv = MeOH, MeCN, H2O; chp stands for deprotonated 6-chloro-2-hydroxypyridine (C5H3ClNO), SALOH stands for monodeprotonated 3,5-ditert-butylsalicylic acid (C15H21O3)) obtained by a solvent-free microwave assisted synthesis method. The Ni(ii) complexes (Ni4Gd, Solv = MeOH; Ni4Dy, Solv = MeCN) are not SMMs in the absence of an applied dc field. The replacement of Ni(ii) by Co(ii) (Co4La, Solv = MeOH; Co4Gd, Solv = H2O; Co4Gd-MeCN, Solv = MeCN; Co4Tb, Solv = MeOH; Co4Dy, Solv = H2O) results in improved SMM properties.

A rapidly-reversible absorptive and emissive vapochromic Pt(II) pincer-based chemical sensor.

Selective, robust and cost-effective chemical sensors for detecting small volatile-organic compounds (VOCs) have widespread applications in industry, healthcare and environmental monitoring. Here we design a Pt(II) pincer-type material with selective absorptive and emissive responses to methanol and water. The yellow anhydrous form converts reversibly on a subsecond timescale to a red hydrate in the presence of parts-per-thousand levels of atmospheric water vapour. Exposure to methanol induces a similarly-rapid and reversible colour change to a blue methanol solvate. Stable smart coatings on glass demonstrate robust switching over 104 cycles, and flexible microporous polymer membranes incorporating microcrystals of the complex show identical vapochromic behaviour. The rapid vapochromic response can be rationalised from the crystal structure, and in combination with quantum-chemical modelling, we provide a complete microscopic picture of the switching mechanism. We discuss how this multiscale design approach can be used to obtain new compounds with tailored VOC selectivity and spectral responses.

Guest-tuned spin crossover in flexible supramolecular assemblies templated by a halide (Cl-, Br- or I-).

Ligand 1,3-bis(3-(pyridin-2-yl)-1H-pyrazol-5-yl)benzene, L, forms mononuclear spin crossover complexes [FeL3]2+ with pendant arms that cause them to dimerize through numerous intermolecular interactions forming supramolecular (X@[FeL3]2)3+ cations. They have the flexibility to encapsulate Cl-, Br- or I-, which allow tuning the magnetic properties, in the solid state and in solution.

Structural and spectroscopic studies of a rare non-oxido V(v) complex crystallized from aqueous solution.

A non-oxido V(v) complex with glutaroimide-dioxime (H3L), a ligand for recovering uranium from seawater, was synthesized from aqueous solution as Na[V(L)2]·2H2O, and the structure determined by X-ray diffraction. It is the first non-oxido V(v) complex that has been directly synthesized in and crystallized from aqueous solution. The distorted octahedral structure contains two fully deprotonated ligands (L3-) coordinating to V5+, each in a tridentate mode via the imide N (R V-N = 1.96 Å) and oxime O atoms (R V-O = 1.87-1.90 Å). Using 17O-labelled vanadate as the starting material, concurrent 17O/51V/1H/13C NMR, in conjunction with ESI-MS, unprecedentedly demonstrated the stepwise displacement of the oxido V[double bond, length as m-dash]O bonds by glutaroimide-dioxime and verified the existence of the "bare" V5+/glutaroimide-dioxime complex, [V(L)2]-, in aqueous solution. In addition, the crystal structure of an intermediate 1 : 1 V(v)/glutaroimide-dioxime complex, [VO2(HL)]-, in which the oxido bonds of vanadate are only partially displaced, corroborates the observations by NMR and ESI-MS. Results from this work provide important insights into the strong sorption of vanadium on poly(amidoxime) sorbents in the recovery of uranium from seawater. Also, because vanadium plays important roles in biological systems, the syntheses of the oxido and non-oxido V5+ complexes and the unprecedented demonstration of the displacement of the oxido V[double bond, length as m-dash]O bonds help with the on-going efforts to develop new vanadium compounds that could be of importance in biological applications.

Molecular self-recognition: a chiral [Mn(II)6] wheel via donor-acceptor π···π contacts and H-bonds.

A multinucleating ligand capable of establishing different types of intermolecular interactions, when combined with acetate groups leads to the assembly of a chiral [Mn(II)3] cluster poised for a process of self-recognition through a combination of perfectly complementary weak forces.

New coordination features; a bridging pyridine and the forced shortest non-covalent distance between two CO32- species.

The aerobic reaction of the multidentate ligand 2,6-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-pyridine, H4L, with Co(ii) salts in strong basic conditions produces the clusters [Co4(L)2(OH)(py)7]NO3 (1) and [Co8Na4(L)4(OH)2(CO3)2(py)10](BF4)2 (2). Analysis of their structure unveils unusual coordination features including a very rare bridging pyridine ligand or two trapped carbonate anions within one coordination cage, forced to stay at an extremely close distance (dO···O = 1.946 Å). This unprecedented non-bonding proximity represents a meeting point between long covalent interactions and "intermolecular" contacts. These original motifs have been analysed here through DFT calculations, which have yielded interaction energies and the reduced repulsion energy experimented by both CO32- anions when located in close proximity inside the coordination cage.

Cryogenic magneto-caloric effect and magneto-structural correlations in carboxylate-bridged Gd(III) compounds.

Two new infinite coordination chain compounds [Gd(CH3CO2)3(dmf)]∞ (1) and {[Gd(HO(CH2)3CO2)3(H2O)]·H2O}∞ (2) have been obtained attempting to modify a prototype molecular cooler. The structures of both compounds as determined by single-crystal X-ray diffraction are reported, together with a detailed study of their magnetic and thermal properties, describing for both compounds a large magneto-caloric effect. The dominant ferromagnetic interaction present in 2 clearly favours this material at low applied magnetic fields, with respect to 1 that exhibits antiferromagnetic interactions. Magneto-structural correlations of the sign and strength of the magnetic interactions are derived for carboxylato-bridged Gd(III) systems.

A prototype chopper for synchrotron time-resolved crystallographic measurements.

A mechanical x-ray chopper has been designed to perform microsecond time-resolved crystallographic studies at the DIAMOND synchrotron I19 beamline. It consists of two asymmetric absorbers rotating synchronously at frequencies from 0 to 50 Hz in the same direction around a rotation axis that is parallel to the x-ray beam. The duration of the x-ray pulses produced by the chopper is determined by the relative phase between the two blades, which can be adjusted. The chopper system presented in this paper offers a time resolution suitable for conducting in situ experiments that afford the crystal structure of materials while in their transient (>10 micros) photoactivated excited states.

Determination of zinc incorporation in the Zn-substituted gallophosphate ZnULM-5 by multiple wavelength anomalous dispersion techniques.

The location of isomorphously substituted zinc over eight crystallographically different gallium sites has been determined in a single-crystal study of the gallophosphate ZnULM-5, Ga((16-x))Zn(x)(PO(4))(14)(HPO(4))(2)(OH)(2)F(7), [H(3)N{CH(2)}(6)NH(3)](4), 6H(2)O, in an 11 wavelength experiment, using data from Station 9.8, SRS Daresbury. The measurement of datasets around the K edges of both Ga and Zn, as well as two reference datasets away from each absorption edge, was utilized to selectively exploit dispersive differences of each metal atom type in turn, which allowed the major sites of Zn incorporation to be identified as the metal 1 and 3 sites, M1 and M3. The preferential substitution of Zn at these sites probably arises because they are located in double four-ring (D4R) building units which can relax to accommodate the incorporation of hetero atoms. As the crystal is non-centrosymmetric, with space group P2(1)2(1)2, it was also possible to use anomalous differences to corroborate the results obtained from the dispersive differences. These results were obtained firstly from difference Fourier maps, calculated using a phase set from the refined structure from data measured at the Zr K edge. Also, refined dispersive and anomalous occupancies, on an absolute scale, could be obtained using the program MLPHARE, allowing estimates for the Zn incorporation of approximately 22 and 18 at. % at the M1 and M3 sites to be obtained. In addition, f' and f'' values for Ga and Zn at each wavelength could be estimated both from MLPHARE results, and by refinement in JANA2006. The fully quantitative determinations of the dispersive and anomalous coefficients for Ga and Zn at each wavelength, as well as metal atom occupancies over the eight metal atom sites made use of the CCP4's MLPHARE program as well as SHELXL and JANA2006. The results by these methods agree closely, and JANA2006 allowed the ready determination of standard uncertainties on the occupancy parameters, which were for M1 and M3, 20.6 (3) and 17.2 (3) at %, respectively.

The dynamic desorption of krypton from the zeolite chabazite.

Single crystal diffraction studies of the zeolite chabazite show that at high loading krypton atoms are forced to occupy sites with unfavourable interatomic Kr-Kr separations but upon desorption of Kr the remaining Kr atoms can now occupy sites with no such unfavourable separations.

Designed layer assembly: a three-dimensional framework with 74% extra-framework volume by connection of infinite two-dimensional sheets.

A coordination polymer with 74% extra-framework volume is prepared by predictable linking of the honeycomb network to generate a framework-structured solid designed with two distinct connecting ligands.

Diels-Alder adducts of medium-ring carbocyclic dienes prepared by rearrangement of catalytically generated cyclic oxonium ylides.

The novel bicyclic and tricyclic systems dimethyl (4aS*,6S*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexahydro-2H-benzocycloheptene-3,4-dicarboxylate, C(16)H(20)O(6), (I), dimethyl (4aS*,6R*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexahydro-2H-benzocycloheptene-3,4-dicarboxylate, C(16)H(20)O(6), (II), (3aS*,9R*,10aS*,10bR*)-9-methoxy-2-oxa-1,3a,4,6,7,8,9,10,10a,10b-decahydro-3H-cyclohepta[e]indene-1,3,8-trione, C(14)H(16)O(5), (III), and (1S*,2R*,9S*,10aR*)-9-methoxy-8-oxo-1,2,3,5,6,7,8,9,10,10a-decahydrobenzocyclooctene-1,2-dicarboxylic acid, C(15)H(20)O(6), (IV), have been crystallographically characterized, allowing the determination of the relative configuration of the stereogenic centres. The poor quality of the dicarboxylic acid crystals necessitated the use of synchrotron radiation.

Bis[1-hydroxypyridine-2(1H)-thionato-S,O]copper(II).

The crystal structure of the widely used title fungicidal material, [Cu(C(5)H(4)NOS)(2)], has been determined at 150 (2) K from a microcrystalline fragment using synchrotron radiation. The molecule adopts a trans-square-planar configuration, with the Cu atom sited at a crystallographic centre of inversion.

High-pressure single-crystal X-ray diffraction facilities on station 9.8 at the SRS Daresbury Laboratory--hydrogen location in the high-pressure structure of ethanol.

A new high-pressure single-crystal diffraction facility has been constructed on station 9.8 at the Synchrotron Radiation Source, Daresbury Laboratory, for a range of studies on a variety of systems of relevance to physics, chemistry and materials science that would otherwise prove intractable with conventional laboratory-based methods. The station has been equipped with a modified Enraf-Nonius CAD4 four-circle diffractometer for high-pressure studies which can be conveniently, and rapidly, interchanged with the Bruker SMART CCD area-detector system when more routine ambient-pressure diffraction work is to be undertaken. This rapid change-over has been achieved by permanently mounting the CAD4 on its own jacking table, formerly used for the station's white-beam diffraction mode, which allows the alignment of the SMART diffractometer to remain undisturbed when the CAD4 is in use. Early results on the test low-melting-point compound ethanol (CH3CH2OH) reveal that excellent refined structures can be obtained, including the location and refinement of the H atoms, demonstrating that one of the original, and major, objectives of the station has been accomplished.

Isomeric icosaboranes B20H26: the synchrotron structure of 1,1'-bis(nido-decaboranyl).

An isomer of B20H26, isolated from the autolysis of nido-B10H14 in a silent electrical discharge, is shown to be the title compound 1,1'-bis(nido-decaboranyl). The molecule has crystallographic inversion symmetry and a long intercage B-B bond of 1.704 (3) A.

Coordination chemistry of Rh(III) porphyrins: complexes with hydrazine, disulfide, and diselenide bridging ligands.

Rh(III) porphyrin complexes with bridging hydrazine and substituted hydrazine ligands were characterized in solution by (1)H NMR spectroscopy and in the solid state by X-ray diffraction. Addition of further ligand to these species afforded 1:1 complexes in which methylhydrazine and N,N-dimethylhydrazine preferentially bound to the Rh center through the substituted nitrogen atom, as evidenced by (1)H NMR chemical shifts. An alkylated Rh(III) porphyrin was isolated as a decomposition product of the reaction of N,N-dimethylhydrazine with Rh(III) porphyrin in the presence of light and oxygen. Me(2)Se(2) and Me(2)S(2) formed bridging and nonbridging complexes with Rh(III) porphyrin, analogous to that observed with N,N'-dimethylhydrazine.

Variable-temperature microcrystal X-ray diffraction studies of negative thermal expansion in the pure silica zeolite IFR.

Variable-temperature single-crystal X-ray diffraction using a synchrotron X-ray source has allowed the mechanism of negative thermal expansion in the pure silica zeolite IFR to be studied in greater detail than was previously possible over the temperature range 30-557 K. The results have allowed the changes in average atomic position with temperature to be measured and the structural features that are important in negative thermal expansion to be identified. The structure of zeolite IFR can be split into two regions: columns of fused rings that expand with temperature and the intercolumn regions, which tend to contract on heating. These competing changes combine to produce a material that contracts parallel to the crystallographic a and b axes and expands in the c-direction. Correlations between zeolite structure and thermal expansivity are also reported.

Stiff, and sticky in the right places: the dramatic influence of preorganizing guest binding sites on the hydrogen bond-directed assembly of rotaxanes.

Structural rigidity and the preorganization of thread binding sites are shown to have a major influence on template efficiency in the synthesis of hydrogen bond-assembled rotaxanes. Preorganization is so effective, in fact, that with good hydrogen bond acceptors (amides) a "world record" yield of 97% for a [2]rotaxane is obtained. The truly remarkable feature of this efficient template, however, is that it allows even poor hydrogen bond acceptors (esters) to be used to prepare hydrogen bond-assembled rotaxanes, despite the presence of competing hydrogen bonding groups (anions) which bind the key intermediates at least 10000x more strongly than single, unorganized, ester groups! The structures of the rotaxanes are established unambiguously in solution by (1)H NMR spectroscopy and in the solid state by X-ray crystallography. As a series they provide unique experimental information regarding the nature of amide-ester hydrogen bonding interactions; in particular they suggest that in CDCl(3), amide-ester NH...O=C hydrogen bonds are approximately 1 kcal mol(-)(1) weaker than the corresponding amide-amide interactions.

Rh(III) porphyrins as building blocks for porphyrin coordination arrays: from dimers to heterometallic undecamers.

The coordination chemistry of a Rh(III) porphyrin building block was investigated with a view to the construction of heterometallic arrays of porphyrins. The Rh(III) porphyrin was found to coordinate methanol in the solid state and weakly in CDCl(3) solution. Crystallization afforded five coordinate pi stacked Rh(III) porphyrins. The distribution of products from reaction of Rh(III) porphyrin with DABCO, 4,4'-bipyridine, and 4,4'-bipyrimidine could be displaced toward dimeric species by silica gel column chromatography or recrystallization which served to remove excess ligand. Weak coordination to nitriles was observed, although it was sufficiently strong to organize a dimeric complex of 5,5'-dicyano-2,2'-bipyridine in the solid state. Complexes with 4,4'-bipyrimidine and 5,5'-dicyano-2,2'-bipyridine possess uncoordinated chelating nitrogen atoms. Larger heterometallic porphyrin arrays were assembled using a combination of Sn(IV) and Rh(III) porphyrin coordination chemistry. A Sn(IV) porphyrin acted as a core around which were coordinated two isonicotinate groups, carboxylic acid functionalized porphyrins, or porphyrin trimer dendrons. Rh(III) porphyrins were coordinated to pyridyl groups at the periphery of these entities. In this way an eleven porphyrin array, with four different porphyrin metalation states, was assembled. The diamagnetic nature of both the Rh(III) and Sn(IV) porphyrins, the slow ligand exchange kinetics on the NMR time scale, and tight ligand binding permitted the porphyrin arrays to be analyzed by two-dimensional (1)H NMR techniques.