In-situ high-pressure powder X-ray diffraction study of α-zirconium phosphate.

The high-pressure structural chemistry of α-zirconium phosphate, α-Zr(HPO4)2·H2O, was studied using in-situ high-pressure diffraction and synchrotron radiation. The layered phosphate was studied under both hydrostatic and non-hydrostatic conditions and Rietveld refinement carried out on the resulting diffraction patterns. It was found that under hydrostatic conditions no uptake of additional water molecules from the pressure-transmitting medium occurred, contrary to what had previously been observed with some zeolite materials and a layered titanium phosphate. Under hydrostatic conditions the sample remained crystalline up to 10 GPa, but under non-hydrostatic conditions the sample amorphized between 7.3 and 9.5 GPa. The calculated bulk modulus, K0 = 15.2 GPa, showed the material to be very compressible with the weak linkages in the structure of the type Zr-O-P.

Fast X-ray powder diffraction on I11 at Diamond.

The commissioning and performance characterization of a position-sensitive detector designed for fast X-ray powder diffraction experiments on beamline I11 at Diamond Light Source are described. The detecting elements comprise 18 detector-readout modules of MYTHEN-II silicon strip technology tiled to provide 90° coverage in 2θ. The modules are located in a rigid housing custom designed at Diamond with control of the device fully integrated into the beamline data acquisition environment. The detector is mounted on the I11 three-circle powder diffractometer to provide an intrinsic resolution of Δ2θ approximately equal to 0.004°. The results of commissioning and performance measurements using reference samples (Si and AgI) are presented, along with new results from scientific experiments selected to demonstrate the suitability of this facility for powder diffraction experiments where conventional angle scanning is too slow to capture rapid structural changes. The real-time dehydrogenation of MgH(2), a potential hydrogen storage compound, is investigated along with ultrafast high-throughput measurements to determine the crystallite quality of different samples of the metastable carbonate phase vaterite (CaCO(3)) precipitated and stabilized in the presence of amino acid molecules in a biomimetic synthesis process.

The effect of pressure on the crystal structure of bianthrone.

Bianthrone [10(10-oxoanthracen-9-ylidene)anthracen-9-one] consists of two tricyclic anthraceneone units connected by a carbon-carbon double bond. Crystals of the form obtained under ambient conditions are yellow and contain folded centrosymmetric conformers in which the central ring of the anthraceneone unit is non-planar. When hydrostatic pressure is applied the crystals assume a red colouration which gradually deepens as pressures increases. The colour change is limited in extent to the surface of the crystals, the bulk remaining yellow. Comparison of high-pressure, single-crystal UV-vis spectra and powder diffraction data demonstrate that the colour change is associated with the formation of a polymorph containing a conformer in which the tricyclic fragments are planar and the molecule is twisted about the central C-C bond. Single-crystal diffraction data collected as a function of pressure up to 6.5 GPa reveal the effect of compression on the yellow form, which consists of layers of molecules which stack along the [010] direction. The structure remains in a compressed form of the ambient-pressure phase when subjected to hydrostatic pressure up to 6.5 GPa, and the most prominent effect of pressure is to push the layers closer together. PIXEL calculations show that considerable strain builds up in the crystal as pressure is increased with a number of intermolecular contacts being pushed into destabilizing regions of their potentials.

Detailed investigations of phase transitions and magnetic structure in Fe(III), Mn(II), Co(II) and Ni(II) 3,4,5-trihydroxybenzoate (gallate) dihydrates by neutron and X-ray diffraction.

The effect of cation valency on the complex structures of divalent and trivalent transition metal gallates has been examined using a combination of neutron and synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and XANES spectroscopy. In the divalent frameworks, M(C(7)H(4)O(5))·2H(2)O (M = Mn, Co and Ni), it was found that charge balance was achieved via the presence of protons on the meta-hydroxyl groups. It was also established that these compounds undergo a discontinuous phase transition at lower temperatures, which is driven by the position of the extra-framework water molecules in these materials. By contrast, in the trivalent Fe gallate, Fe(C(7)H(3)O(5))·2H(2)O, it was found that the stronger bonding between the meta-hydroxy oxygen and the cations leads to a weakening of the bond between this oxygen and its proton. This is turn is thought to lead to stronger hydrogen bonding with the extra-framework water. The lattice water is disordered in the Fe(III) case, which prevents the phase transition found in the M(II) gallates. Refinement against the neutron diffraction patterns also revealed that the relatively mild microwave synthesis of gallate frameworks in D(2)O led to an extensive deuteration of the ortho-hydrogen sites on the aromatic ring, which may suggest a more versatile method of deuterating aromatic organics. The antiferromagnetic structure of Co gallate has also been determined.

The effect of pressure on the crystal structure of [Gd(PhCOO)3(DMF)]n to 3.7 GPa and the transition to a second phase at 5.0 GPa.

The effect of pressure on the crystal structure of the coordination polymer [Gd(PhCOO)(3)(DMF)](n) has been studied to 5.0 GPa. At ambient pressure the structure is tetragonal (space group P4(2)/n) with the polymers extending along the c-direction of the unit cell; successive Gd atoms are alternately bridged by four benzoates and by two benzoates; the coordination spheres of the metal atoms are completed by DMF ligands. This results in two different Gd...Gd repeats, measuring 3.8953(3) and 5.3062(3) A, respectively. The polymer chains interact with each other via dispersion interactions, including a number of CH...pi contacts to phenyl rings in which the H...ring-centroid distances are 3.19 to 3.28 A. Up to 3.7 GPa the crystal remains in a compressed form of its ambient-pressure phase. The a-axis shortens by 7.7%, and the c-axis by 2.9%, the difference reflecting the greater ease of compression along the crystallographic directions mediated by weak intermolecular interactions. At ambient pressure the Gd-O distances span 2.290(2)-2.559(2) A, with an average of 2.39(3) A. At 3.7 GPa the corresponding parameters are 2.259(3) to 2.509(4) and 2.36(3) A. The Gd...Gd distances shortened by 0.0467(4) and 0.1851(4) A, and the CH...pi distances span the range 2.76-2.90 A. During compression a number of H...H contacts develop, the shortest measuring 1.84 A at 3.7 GPa. On increasing the pressure to 5.0 GPa a phase transition occurred in which the shortest H...H contact is relieved by conversion of an edge-to-edge phenyl-phenyl contact into a pi...pi stacking interaction. The new phase is also tetragonal, space group P4, the inversion symmetry present in phase-I being lost in phase-II. The phase transition allows more efficient packing of ligands, and while the a-axis decreases in length the c-axis increases. This leads to Gd...Gd distances of 3.8373(4) and 5.3694(4) A, the latter being longer than at ambient pressure. Gd-O distances at 5.0 GPa span the range 2.265(5) to 2.516(5) A, with a mean of 2.36(2) A.

Pressure-induced Jahn-Teller switching in a Mn12 nanomagnet.

Pressure-induced switching of a fast-relaxing single-molecule magnet to a slow-relaxing isomer is observed for the first time by using a combination of high pressure single-crystal X-ray diffraction and high pressure magnetic measurements.

High pressure studies of hydroxo-bridged Cu(II) dimers.

A combination of high pressure single crystal X-ray diffraction and high pressure SQUID magnetometry has been used to study three hydroxo-bridged copper(II) dimers. [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (1; tmen = tetramethylethylenediamine), [Cu2(OH)2(tben)2](ClO4)2 (2; tben = di-tbutylethylenediamine) and [Cu2(OH)2(bpy)2](BF4)2 (3; bpy = 2,2'-bipyridine) have been structurally determined to 2.5, 0.9 and 4.7 GPa, respectively. The application of hydrostatic pressure imposes significant distortions and modifications in the structures of all three complexes. This is particularly true of the bond distances and angles between the metal centres and the bridging hydroxo groups. Compound 1 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in changes in the magnetic behaviour of the complexes as seen in dc susceptibility measurements up to approximately 0.9 GPa for 1, 2 and 3: the exchange becomes less antiferromagnetic in 1 and 2 and more ferromagnetic in 3.

Comparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transition.

We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), L-cysteic acid monohydrate (CAM) and S-4-sulfo-L-phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8 GPa. CAM contains bi-layers of L-cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8 GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1 GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S-4-sulfo-L-phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9 GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4 GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5 GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids.

High pressure effects on a trimetallic Mn(II/III) SMM.

A combined study of the high pressure crystallography and high pressure magnetism of the complex [Mn3(Hcht)2(bpy)4](ClO4)3.Et2O.2MeCN (1.Et2O.2MeCN) (H3cht is cis,cis-1,3,5-cyclohexanetriol) is presented in an attempt to observe and correlate pressure induced changes in its structural and physical properties. At 0.16 GPa the complex 1.Et2O.2MeCN loses all associated solvent in the crystal lattice, becoming 1. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making the magnetic exchange between the manganese ions weaker. No significant variations are observed in the Jahn-Teller axis of the only Mn(III) present in the structure. High pressure dc chiMT plots display a gradual decrease in both the low temperature value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|.

High pressure induced spin changes and magneto-structural correlations in hexametallic SMMs.

The first combined high pressure single-crystal X-ray diffraction and high pressure magnetism study of two polymetallic clusters is presented in an attempt to correlate the observed changes in structure with changes in magnetic response without the need for changes in external ligation. At 1.5 GPa the structure of [Mn(6)O(2)(Et-sao)(6)(O(2)CPh(Me)(2))(2)(EtOH)(6)] (1; Et-saoH(2) = 2-hydroxyphenylpropanone)--a single molecule magnet (SMM) with an effective anisotropy barrier of approximately 86 K--and of [Mn(6)O(2)(Et-sao)(6)(O(2)C-naphth)(2)(EtOH)(4)(H(2)O)(2)] 2 both undergo significant structural distortions of their metallic skeletons, which has a direct effect upon the observed magnetic response. The application of hydrostatic pressure on the two compounds (up to 1.5 GPa) flattens the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc chi(M)T plots display a gradual decrease in the low temperature peak height and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The "ground states" change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (chi(M)(//)) ac data show a large decrease in the effective energy barrier for magnetisation reversal.

A novel facility using a Laue focusing monochromator for high-pressure diffraction at the SRS, Daresbury, UK.

A novel Laue focusing monochromator has been developed to provide intense X-radiation for high-pressure diffraction experiments. A beamline using this monochromator has been successfully developed on station 9.5 at the SRS, Daresbury Laboratory. Contributions to resolution from monochromator bandpass and divergence due to focusing have been quantified and are used to assess experimental diffraction data from diamond-anvil cells recorded using image plates with X-rays at approximately 30 keV. This optical and beamline design could be readily adapted to use X-rays from a bending magnet on a third-generation synchrotron source.