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The crystal structures of the isostructural title compounds poly[(μ-benzene-1,4-dithiolato)dithallium], Tl(2)(SC(6)H(4)S), and poly[(μ-benzene-1,4-diselenolato)dithallium], Tl(2)(SeC(6)H(4)Se), were solved by simulated annealing from high-resolution synchrotron X-ray powder diffraction. Rietveld refinements of an initial structure with one formula unit per triclinic cell gave satisfactory agreement with the data, but led to a structure with impossibly close non-bonded contacts. A disordered model was proposed to alleviate this problem, but an alternative supercell structure leads to slightly improved agreement with the data. The isostructural superlattice structures were confirmed for both compounds through additional data collection, with substantially better counting statistics, which revealed the presence of very weak superlattice peaks not previously seen. Overall, each structure contains Tl-S or Tl-Se two-dimensional networks, connected by phenylene bridges. The sulfur (or selenium) coordination sphere around each thallium is a highly distorted square pyramid or a 'see-saw' shape, depending upon how many Tl-S or Tl-Se interactions are considered to be bonds. In addition, the two compounds contain pairs of Tl(I) ions that interact through a closed-shell 'thallophilic' interaction: in the sulfur compound there are two inequivalent pairs of Tl atoms with Tl-Tl distances of 3.49 and 3.58 Å, while in the selenium compound those Tl-Tl interactions are at 3.54 and 3.63 Å.

Mn(II)(TCNE)I(OH(2)) was isolated from the reaction of tetracyanoethylene (TCNE) and MnI(2)(THF)(3), and has a 2-D structure possessing an unusual, asymmetric bonded μ(4)-[TCNE]˙(-). Direct antiferromagnetic coupling between the S = 5/2 Mn(II) and S = 1/2 [TCNE]˙(-) leads to magnetic ordering as a canted antiferrimagnet at a T(c) of 171 K.

The M-[TCNE] (M = 3d metal; TCNE = tetracyanoethylene) system is one of the most interesting classes of molecule-based magnets, exhibiting a plethora of compositions and structures (inorganic polymer chains, 2D layers, 3D networks, and amorphous solids) with a wide range of magnetic ordering temperatures (up to 400 K). A systematic study of vibrational (both infrared and, for the first time, Raman) properties of the family of new TCNE-based magnets of M(II)(TCNE) (NCMe)(2)[SbF(6)] [M = Mn, Fe, Ni] composition is discussed in conjunction with their magnetic behavior and newly reso-lved crystal structures. The vibrational properties of the isolated TCNE(●-) anion in the paramagnetic Bu(4)N [TCNE(●-)] salt and recently characterized 2D layered magnet Fe(II)(TCNE)(NCMe)(2)[FeCl(4)] are also reported for comparison. Additionally, a linear correlation between ν(C=C) (a(g)) frequency of the TCNE ligand and its formal charge Z (the spin density on the π* orbital), Z = [1571 - ν(C=C) (a(g))]/154.5 [e], is presented. It is shown that monitoring Z by Raman spectroscopy is of great use in providing information that allows understanding the peculiarity of the superexchange interaction in M-[TCNE] magnets and establishing the structure-magnetic properties correlations in this class of magnetic material.

[Ni(HF(2))(pyz)(2)]X {pyz = pyrazine; X = PF(6)(-) (1), SbF(6)(-) (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN(4)F(2) octahedra. At 298 K, 1 is monoclinic (C2/c) with unit cell parameters, a = 9.9481(3), b = 9.9421(3), c = 12.5953(4) Å, and β = 81.610(3)° while 2 is tetragonal (P4/nmm) with a = b = 9.9359(3) and c = 6.4471(2) Å and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the c-axis which are linked via μ-pyz bridges in the ab-plane to afford three-dimensional polymeric frameworks with PF(6)(-) and SbF(6)(-) counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni-F-H bonds are bent (∼157°) in 1 but are linear in 2. Ligand field calculations (LFT) based on an angular overlap model (AOM), with comparison to the electronic absorption spectra, indicate greater π-donation of the HF(2)(-) ligand in 1 owing to the bent Ni-F-H bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and λ-like peaks in dχT/dT at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (T(N)). Muon-spin relaxation and specific heat studies confirm these T(N)'s. A comparative analysis of χ vs T to various 1D Heisenberg/Ising models suggests moderate antiferromagnetic interactions, with the primary interaction strength determined to be 3.05/3.42 K (1) and 5.65/6.37 K (2). However, high critical fields of 19 and 37.4 T obtained from low temperature pulsed-field magnetization data indicate that a single exchange constant (J(1D)) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (J(⊥)), as mediated by Ni-pyz-Ni, and single-ion anisotropy (D), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of J(⊥) and D based solely on powder data, further support offered by related Ni(II)-pyz compounds and our LFT and density-functional theory (DFT) results lead us to a consistent quasi-1D magnetic description for 1 and 2., (© 2011 American Chemical Society)

A non-diffracting surface layer exists at any boundary of a crystal and can comprise a mass fraction of several percent in a finely divided solid. This has led to the long-standing issue of amorphous content in standards for quantitative phase analysis (QPA). NIST standard reference material (SRM) 676a is a corundum (α-Al(2)O(3)) powder, certified with respect to phase purity for use as an internal standard in powder diffraction QPA. The amorphous content of SRM 676a is determined by comparing diffraction data from mixtures with samples of silicon powders that were engineered to vary their specific surface area. Under the (supported) assumption that the thickness of an amorphous surface layer on Si was invariant, this provided a method to control the crystalline/amorphous ratio of the silicon components of 50/50 weight mixtures of SRM 676a with silicon. Powder diffraction experiments utilizing neutron time-of-flight and 25 keV and 67 keV X-ray energies quantified the crystalline phase fractions from a series of specimens. Results from Rietveld analyses, which included a model for extinction effects in the silicon, of these data were extrapolated to the limit of zero amorphous content of the Si powder. The certified phase purity of SRM 676a is 99.02% ± 1.11% (95% confidence interval). This novel certification method permits quantification of amorphous content for any sample of interest, by spiking with SRM 676a.

α-SrCr(2)O(4) has a triangular planar lattice of d(3) Cr(3+) made from edge sharing CrO(6) octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of - 596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi-two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0, 0.3217(8), 0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-plane spacing on cooling below 100 K and an inflection in the cell parameters at the magnetic ordering temperature. These anomalies indicate the presence of a moderate degree of magnetostructural coupling.

Metal-organic frameworks based on metal-sulfur or metal-selenium bonds are relatively rare; herein we describe the synthesis and structural characterization of several examples, including, for example, [Cd(en)3][Cd(SC6H4S)2], which contains the anionic two-dimensional square-grid network [Cd(SC6H4S)2]n(2n-).

The reaction of Mn(II) and KCN in aqueous and non-aqueous media leads to the isolation of three-dimensional (3-D) Prussian blue analogues, K(2)Mn[Mn(CN)(6)] (1a-d, 1e, respectively). Use of RbCN forms Rb(2)Mn[Mn(CN)(6)] (2). 1 and 2 are isomorphic {monoclinic, P2(1)/n: 1 [a = 10.1786(1) A, b = 7.4124(1) A, c = 6.9758(1) A, beta = 90.206(1)(o)]; 2 [a = 10.4101(1) A, b = 7.4492(1) A, c = 7.2132(1) A, beta = 90.072(1)(o)]}, with a small monoclinic distortion from the face centered cubic (fcc) structure that is typical of Prussian blue structured materials that was previously reported for K(2)Mn[Mn(CN)(6)]. Most notably the average Mn-N-C angles are 148.8 degrees and 153.3 degrees for 1 and 2, respectively, which are significantly reduced from linearity. This is attributed to the ionic nature of high spin Mn(II) accommodating a reduced M-CN-M' angle and minimizing void space. Compounds 1a,b have a sharp, strong nu(OH) band at 3628 cm(-1), while 1e lacks a nu(OH) absorption. The nu(OH) absorption in 1a,b is attributed to surface water, as use of D(2)O shifts the nu(OH) absorption to 2677 cm(-1), and that 1a-e are isostructural. Also, fcc Prussian blue-structured Cs(2)Mn[Mn(CN)(6)] (3) has been structurally [Fm3m: a = 10.6061(1) A] and magnetically characterized. The magnetic ordering temperature, T(c), increases as K(+) (41 K) > Rb(+) (34.6 K) > Cs(+) (21 K) for A(2)Mn[Mn(CN)(6)] in accord with the increasing deviation for linearity of the Mn-N-C linkages [148.8 (K(+)) > 153.3 (Rb(+)) > 180 degrees (Cs(+))], decreasing Mn(II)...Mn(II) separations [5.09 (K(+)) < 5.19 (Rb(+)) < 5.30 A (Cs(+))], and decreasing size of the cation (increasing electrostatic interactions). Hence, the bent cyanide bridges play a crucial role in the superexchange mechanism by increasing the coupling via shorter Mn(II)...Mn(II) separations, and perhaps enhanced overlap. In addition, the temperature dependent magnetic behavior of K(4)[Mn(II)(CN)(6)].3H(2)O is reported.

In 2-ethoxybenzamide, C(9)H(11)NO(2), the amide substituents are linked into centrosymmetric head-to-head hydrogen-bonded dimers. Additional hydrogen bonds between adjacent dimers give rise to ribbon-like packing motifs, which extend along the c axis and possess a third dimension caused by twisting of the 2-ethoxyphenyl substituent with respect to the hydrogen-bonded amide groups. The ribbons are arranged in a T-shaped herringbone pattern and cohesion between them is achieved by van der Waals forces.

In this Letter we show that superconducting Fe(1.01)Se undergoes a structural transition at 90 K from a tetragonal to an orthorhombic phase but that nonsuperconducting Fe(1.03)Se does not. High resolution electron microscopy at low temperatures further reveals an unexpected additional modulation of the crystal structure of the superconducting phase that involves displacements of the Fe atoms, and that the nonsuperconducting composition shows a different, complex nanometer-scale structural modulation. Finally, we show that magnetism is not the driving force for the phase transition in the superconducting phase.

H(x)K(1-x)M(II)[Ru(2)(CO(3))(4)](H(2)O)(y)(MeOH)(z) (M = Mn, Fe, Co, Ni, Mg) were synthesized from the reaction of M(II) and K(3)[Ru(2)(CO(3))(4)] in water and are isomorphous with an orthorhombic three-dimensional network structures based on mu(3)-CO(3)(2-) linkages to Ru(2) moieties forming layers and also to trans-M(II)(OH(2))(4) sites forming linked chains that connect the layers. They, as well as non-isomorphous M = Cu, magnetically order as canted ferrimagnets with T(c) = 4.4 +/- 1.0 K. The presence of S = 0 M(II) = Mg(II) has essentially no effect on T(c) suggesting that the main magnetic pathway does not occur the through M(II)-based chains, but only via Ru(2)...Ru(2) linkages that reside in layers. This is a rare example of a magnet based upon a second row transition metal.

The reaction of Cr(C(6)H(6))(2) and 1,2,4,5-tetracyanopyrazine (TCNP) forms [Cr(C(6)H(6))(2)][TCNP], and TCNP is reduced and forms the eclipsed pi-[TCNP](2)(2-) dimer. Diamagnetic [TCNP](2)(2-) has an intradimer separation of 3.14(2) A. The intradimer C...C and N...N separations are 3.29(2) and 3.42(2) A, respectively, and increase with the distance from the center of the molecule, due to nitriles bending away from the plane of the molecule by 5 +/- 1 degrees. [TCNP](2)(2-) is best described by an atoms-in-molecules analysis as having a 2e(-)/8c C-C bond involving the four C atoms from each six-member ring. The results of B3LYP/6-31+G(d)-computed interactions indicate that the [TCNP](*-)...[TCNP](*-) interactions in an isolated [TCNP](2)(2-) are repulsive by 58.9 kcal/mol, and that the stability of [TCNP](2)(2-) primarily originates from [TCNP](*-)...cation(+) electrostatic interactions, whose sum (-209.8 kcal/mol) exceeds the sum of the repulsive [TCNP](*-)...[TCNP](*-) and cation(+)...cation(+) interactions (140.3 kcal/mol).

The structures of three temperature-dependent polymorphs of solvent-free decamethylferrocenium tetracyanoethenide, [FeCp*(2)][TCNE], are determined from high-resolution synchrotron powder diffraction data. [FeCp*(2)][TCNE] is the first organic-based ferromagnetic material to be synthesized and is known to have two structural phase transitions at 249 and 282 K. The low-temperature phase, which exhibits spontaneous ferromagnetic order below 4.8 K, was determined at 12 K. At that temperature, it has monoclinic space group P2(1)/c [a = 9.6637(4) A, b = 14.1217(5) A, c = 18.6256(7) A, beta = 113.231(2) degrees, Z = 4] and consists of parallel chains of alternating [Fe(C(5)Me(5))(2)](*+) and [TCNE](*-) ions, with an intrachain Fe...Fe distance of 10.45 A. Structures of the intermediate and ambient temperature phases, also studied here, are characterized by increasing disorder. At 250 K, the unit cell space group is P2(1)/m [a = 9.7100(3) A, b = 14.4926(4) A, c = 9.4997(3) A, beta = 113.153(1) degrees, Z = 2]. At ambient temperature, the lattice, albeit quite disordered, belongs to the orthorhombic space group Cmcm [a = 10.629(1) A, b = 16.128(1) A, c = 14.593(1) A, Z = 4]. Nearest-neighbor magnetic interactions were evaluated for the 12 K structure by CASSCF and CASSCF/MCQDPT calculations (a methodology similar to the CASPT2 method). Similar trends are observed in computations with and without inclusion of spin-orbit coupling. The strongest are two intrachain [FeCp*(2)](*-)...[TCNE](*-) interactions (ferromagnetic with values of approximately 45 and approximately 29 cm(-1)), although weaker, nonnegligible, ferro- or antiferromagnetic interchain interactions of less than +/-0.2 cm(-1) are also present. Magnetic interactions that lead to ordering are therefore three-dimensional, despite the vastly different intra- and interchain coupling strengths.

X-ray powder diffraction and magnetic susceptibility measurements show that Ag(pyz)(2)(S(2)O(8)) consists of 2D square nets of Ag(2+) ions resulting from the corner-sharing of axially elongated AgN(4)O(2) octahedra and exhibits characteristic 2D antiferromagnetism. Nevertheless, mu(+)SR measurements indicate that Ag(pyz)(2)(S(2)O(8)) undergoes 3D magnetic ordering below 7.8(3) K.

The discovery of ligands that bind specifically to a targeted protein benefits from the development of generic assays for high-throughput screening of a library of chemicals. Protein powder diffraction (PPD) has been proposed as a potential method for use as a structure-based assay for high-throughput screening applications. Building on this effort, powder samples of bound/unbound states of soluble hen-egg white lysozyme precipitated with sodium chloride were compared. The correlation coefficients calculated between the raw diffraction profiles were consistent with the known binding properties of the ligands and suggested that the PPD approach can be used even prior to a full description using stereochemically restrained Rietveld refinement.

Physical property measurements on samples of triangular-lattice NaVO2 reveal two successive orbital ordering transitions. At 300 K, the structure is rhombohedral. At 98 K, the system undergoes a second-order transition to a monoclinic phase in which the in-plane V-V distances separate into four short and two long bonds, corresponding to orbital ordering of one electron per V3+. Below 93 K, there is a first-order transition to a second monoclinic phase with four long and two short V-V bonds, consistent with orbital ordering of two electrons per V3+. Long range magnetic ordering of 0.98(2)mu&#95;(B) per V3+ (3d(2)) sets in at the 93 K structural transition. The orbital ordering relieves the geometric frustration and leads to a magnetically ordered ground state.

The ammonia complex of magnesium borohydride Mg(BH4)2.2NH3 (I), which contains 16.0 wt % hydrogen, is a potentially promising material for hydrogen storage. This complex was synthesized by thermal decomposition of a hexaaammine complex Mg(BH4)2.6NH3 (II), which crystallizes in the cubic space group Fm3 m with unit cell parameter a=10.82(1) A and is isostructural to Mg(NH3) 6Cl2. We solved the structure of I that crystallizes in the orthorhombic space group Pcab with unit cell parameters a=17.4872(4) A, b=9.4132(2) A, c=8.7304(2) A, and Z=8. This structure is built from individual pseudotetrahedral molecules Mg(BH4)2.2NH3 containing one bidentate BH4 group and one tridentate BH4 group that pack into a layered crystal structure mediated by N-H...H-B dihydrogen bonds. Complex I decomposes endothermically starting at 150 degrees C, with a maximum hydrogen release rate at 205 degrees C, which makes it competitive with ammonia borane BH 3NH3 as a hydrogen storage material.

The reactions of Pb(OAc)2 with 1,2,4,5-benzenetetrathiol, 1,4-benzenedithiol, and benzenehexathiol in ethylenediamine yield bright yellow [Pb2(S2C6H2S2)(en)]n, orange-red [Pb3(SC6H4S)3(en)2]n, and brown [Pb3C6S6]n, respectively. The structures of [Pb2(S2C6H2S2)(en)]n and [Pb3C6S6]n were solved by synchrotron X-ray powder diffraction, while the structure of [Pb3(SC6H4S)3(en)2]n was solved by single-crystal X-ray diffraction. The bonding in [Pb2(S2C6H2S2)(en)]n indicates the presence of "molecular" units, while in [Pb3C6S6]n, the bonding most resembles that in an inorganic solid such as PbS. The differences in bonding are reflected in the optical and electrical properties of the materials; [Pb3C6S6]n is a semiconductor.

K(x)H(1-x)Ni(OH2)4[Ru2(CO3)4].zH2O is a ferrimagnet (Tc = 4.3 K) formed from the reaction of K3[Ru(II/III)2(CO3)4] and Ni(II) in water. It possesses a new 3-D network structural motif composed of linked chains and mu3-CO3 linkages to both Ru and Ni sites. Each Ni(II) bonds to four oxygens and to two [Ru2(CO3)4]3- moieties in a cis manner, and four mu3-CO3 groups from each [Ru2(CO3)4](3-) have two oxygens bonding to the Ru2 moiety, forming the typical paddle-wheel core, and trans pairs of the third CO32- oxygen axially bonded to either another Ru2 or Ni(II).

We have determined the structures of two phases of unsolvated Mg(BH(4))(2), a material of interest for hydrogen storage. One or both phases can be obtained depending on the synthesis conditions. The first, a hexagonal phase with space group P6(1), is stable below 453 K. Upon heating above that temperature it transforms to an orthorhombic phase, with space group Fddd, stable to 613 K at which point it decomposes with hydrogen release. Both phases consist of complex networks of corner-sharing tetrahedra consisting of a central Mg atom and four BH(4) units. The high-temperature orthorhombic phase has a strong antisite disorder in the a lattice direction, which can be understood on the basis of atomic structure.

The cocrystal of celecoxib and nicotinamide (Cel:Nic) was crystallized from chloroform in a 1:1 ratio, and the structure has been solved from powder X-ray diffraction data. The dissolution and solubility of Cel:Nic are medium dependent and can be attributed to differences in conversion of Cel:Nic to celecoxib polymorphs I and III (Cel-I and Cel-III). The presence of low concentrations of surfactants facilitates the rapid conversion of neat Cel:Nic to large aggregates of Cel-III that dissolve more slowly than commercial Cel-III into 1% SDS solution. In contrast, combinations of Cel:Nic with both 1-10% solid SDS and PVP wet rapidly and convert to a mixture of amorphous celecoxib and a micron-sized crystalline celecoxib form IV (Cel-IV), which has recently been shown to be up to 4-fold more bioavailable than marketed Cel-III. More than 90% of the suspended material dissolves within 2 min at 37 degrees C when transferred to 1% SDS solution. This example highlights the importance of exploring the form conversion of cocrystals in aqueous media prior to pharmacokinetic studies, and illustrates the potential of simple formulations to overcome the limitations caused by rapid dissociation of cocrystals and recrystallization of poorly soluble forms in aqueous media.

MIICl2 (M = Mn, Fe, Co) as their acetonitrile solvates were isolated, and their structural, spectroscopic, and magnetic properties were studied. MCl2(NCMe)2 (M = Fe, Mn) form 1-D chains of octahedral MII ions with four bridging chlorides and two axial MeCN's. The presence of an axial distortion for MFe causes a significant magnetic anisotropy that increases significantly below 150 K; however, chiav [=(chi parallel + 2chi perpendicular)/3] almost coincides with the value obtained on a polycrystalline sample. MnCl2(NCMe)2 is a paramagnet with a weak antiferromagnetic coupling. Annealing FeCl2(NCMe)2 at 55 degrees C forms the monosolvate of FeCl2(NCMe) composition in which two chains collapse into a double chain with formation of Fe-Cl bonding such that half of the mu-Cl's becomes mu3-Cl's. This material orders magnetically below Tc = 4.3 K. For M = Co, paramagnetic tetrahedral [CoCl3(NCMe)]- anions are isolated.

[Fe(TCNE)(NCMe)2][FeCl4] is isolated from the reaction of TCNE and FeCl2(NCMe)2 and orders as a ferrimagnet below 90 K and is the initial member of a new class of magnets. It is the first metal-TCNE magnet with direct bonding between metal ion and [TCNE]*- whose structure has been determined, and it possesses a novel planar mu4-[TCNE]*- spin coupling unit bonded to four FeII's, with an axial pair of MeCNs. The [FeIIICl4]- anion occupies sites between the [FeII(TCNE*-)(NCMe)2]+ layers. [Fe(TCNE)(NCMe)2][FeCl4] has a coercive field of 1730 Oe and a remnant magnetization of 7500 emuK/mol at 50 K.

This study was designed to investigate the physical characteristics and crystalline structure of 2-hydroxy-N-[3(5)-pyrazolyl]-1,4-naphthoquinone-4-imine (PNQ), a new active compound against Trypanosoma cruzi, the causative agent of American trypanosomiasis. Methods used included differential scanning calorimetry, thermogravimetry, hot stage microscopy, polarized light microscopy (PLM), Fourier-transform infrared (FTIR) spectroscopy, and high-resolution X-ray powder diffraction (HR-XRPD). According to PLM and HR-XRPD data, PNQ crystallized as red oolitic crystals (absolute methanol) or prisms (dimethyl sulfoxide [DMSO]-water) with the same internal structure. The findings obtained with HR-XRPD data (applying molecular location methods) showed a monoclinic unit cell [a = 18.4437(1) A, b = 3.9968(2) A, c = 14.5304(1) A, alpha = 90 degrees , beta = 102.71(6) degrees , gamma = 90 degrees , V = 1044.9(1) A(3), Z = 4, space group P2(1)/c], and a crystal structure (excluding H-positions) described by parallel layers in the direction of the b-axis, with molecules held by homochemical (phenyl-phenyl and pyrazole-pyrazole) van der Waals interactions. In addition, FTIR spectra displayed the NH-pyrazole stretch overlapped with the OH absorption at 3222 cm(-1), typical of -NH and -OH groups associated through H-bondings; and a carbonyl stretching absorption at 1694 cm(-1), indicating a nonextensively H-bonded quinonic C=O, which was in accordance with the solved crystal structure of PNQ. The existence of such cohesive forces shed light on the thermoanalytical data, which revealed that PNQ is a stable solid, unaffected by oxygen that decomposed without melting above 260 degrees C.

The three-dimensional solid-state structures of prazosin hydrochloride, C19H22N5O4+.Cl- (A), and prazosin free base, C19H21N5O4 (B), have been determined by synchrotron X-ray powder diffraction. A and B crystallize in triclinic P-1 and monoclinic Cc space groups, respectively, with one structural unit per asymmetric part. In A and B, the prazosin molecule adopts different conformations, which do not correspond to those obtained by DFT optimizations of protonated and free prazosin., ((c) 2004 Wiley-Liss, Inc. and the American Pharmacists Association)

The objectives of this study were (i) to isolate and characterize mannitol hydrate, and (ii) to solve its crystal structure from high-resolution synchrotron X-ray powder diffraction data. Mannitol hydrate was prepared by freeze-drying aqueous mannitol solutions (5% w/v) under controlled conditions. X-ray powder diffractometry, differential scanning calorimetry, and thermogravimetric analyses indicated that mannitol exists as a hemihydrate (C(6)H(14)O(6) . 0.5H(2)O). Synchrotron data were collected on the X3B1 beamline at the National Synchrotron Light Source. The simulated annealing program PSSP was used to solve the structure, which was subsequently refined by Rietveld analysis using the program package GSAS. The compound crystallizes in space group P1, with a = 9.8963 A, b = 10.5424 A, c = 4.7860 A, alpha = 102.589 degrees , beta = 86.092 degrees , and gamma = 116.079 degrees . The unit cell contains two dissimilar D-mannitol molecules and one water molecule, forming a hydrogen bonding pattern significantly different from that seen in the anhydrous polymorphs.

Diruthenium tetracarboxylates monocations are utilized as building blocks for cubic 3-D network structured molecule-based magnets. [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] [M = Cr (1a), Fe (2), Co (3)] were prepared in aqueous solution. Powder X-ray diffraction indicates that they have body-centered cubic structures (space group = Imm, a = 13.34, 13.30, and 13.10 A for 1a, 2, and 3, respectively), which was confirmed for 1a by Reitveld analysis of the synchrotron powder data [a = 13.3756(5) A]. [Ru(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)].xMeCN [M = Cr, x = 1.8 (1b); M = Mn, x = 3.3 (4)] were prepared from acetonitrile. The magnetic ordering of 1a (33 K), 1b (34.5 K), 2 (2.1 K), and 4 (9.6 K) was determined from the temperature dependencies of the in-phase (chi') alternating current (AC) susceptibility. The field dependence of the magnetization, M(H), at 2 K for 1a showed an unusual constricted hysteresis loop with a coercive field, H(cr), of 470 Oe while the M(H) data for 1b, 2, and 4 showed a normal hysteresis loop with a coercive field of 1670, 10, and 990 Oe, respectively. The (57)Fe Mössbauer spectrum of 2 is consistent with the presence of low spin Fe(III) (delta = -0.05 mm/s; DeltaE = 0.33 mm/s) at room temperature, and the onset of 3-D magnetic ordering at lower temperature (<2 K). The effects of M(III) in [M(III)(CN)(6)](3-), and the large zero-field splitting (D) of diruthenium tetracarboxylates are discussed. The increasing critical temperatures T(c), with increasing S could not be accounted for by mean field models without significantly different J values for 1a, 4, and 2. By fitting the T(c) data with mean field models [H = -2JS(Ru).(S(M) - micro(B)(g(Ru)S(Ru) + g(M)S(M))H], J/k(B) are 4.46, 1.90, and 0.70 K for 1a, 4, and 2, respectively.

Nitric oxide's beta-quinol clathrate rapidly and quantitatively releases nitric oxide upon dissolution to give well defined spatiotemporal gradients.

The crystal structure of 2-isopropyl-5-methyl-1,4-benzoquinone (thymoquinone) and its thermal behavior--as necessary physical and chemical properties--were determined in order to enhance the current understanding of thymoquinone chemical action by using high resolution x-ray powder diffraction, Fourier transform infrared spectroscopy (FTIR), and 3 thermo-analytical techniques thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The findings obtained with high-resolution x-ray powder diffraction and molecular location methods based on a simulated annealing algorithm after Rietveld refinement showed that the triclinic unit cell was a = 6.73728(8) A, b = 6.91560(8) A, c = 10.4988(2) A, alpha = 88.864(2) degrees, beta = 82.449(1) degrees, gamma = 77.0299(9) degrees; cell volume = 472.52(1) A3, Z = 2, and space group P1. In addition, FTIR spectrum revealed absorption bands corresponding to the carbonyl and C-H stretching of aliphatic and vinylic groups characteristically observed in such p-benzoquinones. Also, a chemical decomposition process starting at 65 degrees C and ending at 213 degrees C was noted when TGA was used. DSC allowed for the determination of onset at 43.55 degrees C and a melting enthalpy value of DeltaH(m) = 110.6 J/g. The low value obtained for the fusion point displayed a van der Waals pattern for molecular binding, and the thermograms performed evidence that thymoquinone can only be found in crystalline triclinic form, as determined by DRX methods.

The crystal structure of polymorphic Form II of enalapril maleate, a potent angiotensin-converting enzyme inhibitor, was determined from high-resolution X-ray diffraction data using the direct space method. Enalapril maleate Form II crystallizes in space group P2(1)2(1)2(1), Z = 4, with unit cell parameters a = 33.9898(3) A, b = 11.2109(1) A, c = 6.64195(7) A, and V = 2530.96(5) A(3). By treating the molecules as rigid bodies and using the bond lengths and angles obtained from the X-ray single crystal structures of Form I, which were solved almost 20 years ago, the total degrees of freedom of enalapril maleate were reduced from 25 to 12. This reduction in total degrees of freedom allowed the simulated annealing to complete within a reasonable computation time. In the crystal structure of Form II, the crystal packing, hydrogen-bonding pattern, and conformation of enalapril maleate resemble those in the structure of Form I. The crystal packing and conformation of enalapril maleate in the two polymorphic forms may explain the similarity of the thermal properties, (13)C nuclear magnetic resonance, Fourier transform infrared, and Raman spectra of Forms I and II. In both structures, the conformations of the main peptide chains, which are considered responsible for binding the active angiotensin-converting enzyme sites, remain largely unchanged. Lattice energy calculation showed that Form II is slightly more stable than Form I by 3.5 kcal/mole., (Copyright 2003 Wiley-Liss, Inc. and the American Pharmacists Association)

Recent advances in crystallographic computing and availability of high-resolution diffraction data have made it relatively easy to solve crystal structures from powders that would have traditionally required single crystal samples. The success of direct space methods depends heavily on starting with an accurate molecular model. In this paper we address the applicability of using these methods in finding subtleties such as disorder in the molecular conformation that might not be known a priori. We use ranitidine HCl as our test sample as it is known to have a conformational disorder from single crystal structural work. We redetermine the structure from powder data using simulated annealing and show that the conformational disorder is clearly revealed by this method., (Copyright 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:244-249, 2003)

The three-dimensional structure, conformation, and packing of molecules in the solid state are crucial components used in the optimization of many technologically useful materials properties. Single-crystal X-ray diffraction is the traditional and most effective method of determining 3-D structures in the solid state. Obtaining single crystals that are sufficiently large and free of imperfections is often laborious, time-consuming, and, occasionally, impossible. The feasibility of an integrated approach to the determination and verification of a complete three-dimensional structure for a medium-sized organic molecule without using single crystals is demonstrated for the case of an organic stabilizer compound N-(p-tolyl)-dodecylsulfonamide. The approach uses a combination of powder XRD data, several computational packages involving Monte Carlo simulations and ab initio quantum mechanical calculations, and experimental solid-state NMR chemical shifts. Structure elucidation of N-(p-tolyl)-dodecylsulfonamide revealed that the Bravais lattice is monoclinic, with cell dimensions of a = 38.773 A, b = 5.507 A, c = 9.509 A, and beta = 86.35 degrees, and a space group of P21/c.

Hemoglobin digestion in the intraerythrocytic trophozoite stages of the malaria parasite releases large quantities of heme, which is then detoxified by crystallization into regular crystallites, which are subsequently secreted into the host vascular network as malaria pigment. This crystalline product is isostructural with the synthetic phase b-hematin, and its structure, solved from its powder diffraction pattern, (Pagola et al., 2000), corresponds to a hydrogen bonded chain of propionate linked dimers, Figure 1. This is an example where the crystalline phase is the macromolecule of direct biological interest, particularly in light of the currently accepted hypothesis for the quinoline antimalarial drug action being the inhibition of b-hematin formation and biosynthesis. A surprisingly array of spectroscopically similar closely related phases can also form during the reactions which are used to synthesize b-hematin. Scanning electron microscopy and X-ray powder diffraction have been used to characterize these materials. Taken together these results indicate that infrared spectroscopy, in itself, is insufficient to identify synthetic analogs to malaria pigment and that a combination of electronmicroscopy and powder diffraction are required to unambiguously characterize these heme aggregates.

CHCl3 and CHBr3 intercalated C60 have attracted particular interest after a superconductivity transition temperature (Tc) of up to 117 K was discovered. We have determined the structure using synchrotron x-ray powder-diffraction and found that the expansion of the lattice mainly takes place in one dimension (triclinic b axis), leaving planes of C60 molecules on an approximately hexagonal, slightly expanded lattice. We have performed tight-binding band structure calculations for the surface layer. In spite of the slight expansion of the layers, for the range of dopings where a large Tc has been observed, the density of states at the Fermi energy is smaller for C60.2CHCl3 and C60.2CHBr3 than for C60. This suggests that the lattice expansion alone cannot explain the increase of Tc.

Inelastic neutron scattering measurements are presented which show the abrupt development of new oxygen lattice vibrations near the doping-induced metal-insulator transition in La(2--x)Sr(x)CuO(4). A direct correlation is established between these lattice modes and the electronic susceptibility (as measured by photoemission) inferring that such modes mix strongly with charge fluctuations. This electron-lattice coupling can be characterized as a localized one-dimensional response of the lattice to short-ranged metallic charge fluctuations.

X-ray diffraction analysis of protein structure is often limited by the availability of suitable crystals. However, the absence of single crystals need not present an insurmountable obstacle in protein crystallography any more than it does in materials science, where powder diffraction techniques have developed to the point where complex oxide, zeolite and small organic molecular structures can often be solved from powder data alone. Here, that fact is demonstrated with the structure solution and refinement of a new variant of the T(3)R(3) Zn-human insulin complex produced by mechanical grinding of a polycrystalline sample. High-resolution synchrotron X-ray powder diffraction data were used to solve this crystal structure by molecular replacement adapted for Rietveld refinement. A complete Rietveld refinement of the 1630-atom protein was achieved by combining 7981 stereochemical restraints with a 4800-step (d(min) = 3.24 A) powder diffraction pattern and yielded the residuals R(wp) = 3.73%, R(p) = 2.84%, R(F)(2) = 8.25%. It was determined that the grinding-induced phase change is accompanied by 9.5 and 17.2 degrees rotations of the two T(3)R(3) complexes that comprise the crystal structure. The material reverts over 2-3 d to recover the original T(3)R(3) crystal structure. A Rietveld refinement of this 815-atom protein by combining 3886 stereochemical restraints with a 6000-step (d(min) = 3.06 A) powder diffraction pattern yielded the residuals R(wp) = 3.46%, R(p) = 2.64%, R(F)(2) = 7.10%. The demonstrated ability to solve and refine a protein crystal structure from powder diffraction data suggests that this approach can be employed, for example, to examine structural changes in a series of protein derivatives in which the structure of one member is known from a single-crystal study.

Despite the worldwide public health impact of malaria, neither the mechanism by which the Plasmodium parasite detoxifies and sequesters haem, nor the action of current antimalarial drugs is well understood. The haem groups released from the digestion of the haemoglobin of infected red blood cells are aggregated into an insoluble material called haemozoin or malaria pigment. Synthetic beta-haematin (FeIII-protoporphyrin-IX)2 is chemically, spectroscopically and crystallographically identical to haemozoin and is believed to consist of strands of FeIII-porphyrin units, linked into a polymer by propionate oxygen-iron bonds. Here we report the crystal structure of beta-haematin determined using simulated annealing techniques to analyse powder diffraction data obtained with synchrotron radiation. The molecules are linked into dimers through reciprocal iron-carboxylate bonds to one of the propionic side chains of each porphyrin, and the dimers form chains linked by hydrogen bonds in the crystal. This result has implications for understanding the action of current antimalarial drugs and possibly for the design of new therapeutic agents.

The compounds tetrakis(trimethylsilyl)methane C[Si(CH(3))(3)](4) (TC) and tetrakis(trimethylsilyl)silane Si[Si(CH(3))(3)](4) (TSi) have crystal structures with the molecules in a cubic closed-packed (c.c.p.) stacking. At room temperature both structures have space group Fm{\bar 3}m (Z = 4) with a = 13.5218 (1) Å, V = 2472.3 (1) Å(3) for TSi, and a = 12.8902 (2) Å, V = 2141.8 (1) Å(3) for TC. X-ray scattering data can be described by a molecule with approximately sixfold orientational disorder, ruling out a structure with free rotating molecules. Upon cooling, TSi exhibits a first-order phase transition at T(c) = 225 K, as is characterized by a jump of the lattice parameter of Deltaa = 0.182 Å and by an exothermal maximum in differential scanning calorimetry (DSC) with DeltaH = 11.7 kJ mol(-1) and DeltaS = 50.0 J mol(-1) K(-1). The structure of the low-temperature phase is refined against X-ray powder data measured at 200 K. It has space group P2(1)3 (Z = 4), a = 13.17158 (6) Å and V = 2285.15 (2) Å(3). The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as is shown by analyzing distances between atoms and by calculations of the lattice energy in dependence on the orientations of the molecules. TC has a phase transition at T(c1) = 268 K, with Deltaa(1) = 0.065 Å, DeltaH(1) = 3.63 kJ mol(-1) and DeltaS(1) = 13.0 J mol(-1) K(-1). A second first-order phase transition occurs at T(c2) = 225 K, characterized by Deltaa(2) = 0.073 Å, DeltaH(2) = 6.9 kJ mol(-1) and DeltaS(2) = 30.0 J mol(-1) K(-1). The phase transition at higher temperature has not been reported previously. New NMR experiments show a small anomaly in the temperature dependence of the peak positions in NMR to occur at T(c2). Rietveld refinements were performed for the low-temperature phase measured at T = 150 K [space group P2(1)3, lattice parameter a = 12.609 (3) Å], and for the intermediate phase measured at T = 260 K [space group Pa{\bar 3}, lattice parameter a = 12.7876 (1) Å]. The low-temperature phase of TC is formed isostructural to the low-temperature phase of TSi. In the intermediate phase the molecules exhibit a twofold orientational disorder.

We report the ab initio structure solutions of two solvent containing potassium phenoxides by high-resolution powder X-ray diffraction. Both compounds are of interest for the classification of the mechanism of Kolbe-Schmitt type reactions. C(6)H(5)OK.2C(6)H(5)OH crystallizes in space group Abm2, Z = 4, with unit cell parameters a = 10.12458(4) Å, b = 21.2413(1) Å, c = 7.89784(3) Å. C(6)H(5)OK.3C(6)H(5)OH crystallizes in space group Pbca, Z = 8, with unit cell parameters a = 22.7713(1) Å, b = 25.4479(2) Å, c = 7.75549(4) Å. Both compounds show polymeric zigzag chains [K([6])O(2)([2])O([1])pi(phenyl)([1])] aligned along the c-axis. The coordination of the potassium ions is similar for both compounds. They lie at the center of distorted octahedra of five oxygen atoms and one phenyl ring, which donates its pi electrons. The distortion decreases as the number of free phenol increases.

The microcrystalline organometallic coordination polymer [Ru(2){&mgr;(2):&mgr;(2):eta(2)-O(2)PMe(2)}(2)(CO)(4)](n)() which results from the oxidative addition of dimethylphosphinic acid to triruthenium dodecacarbonyl has been structurally characterized by X-ray powder diffraction, lambda = 1.149 49(1) Å, at 295 and 50 K. At room temperature the crystallites have a monoclinic unit cell with the space group C2/c with lattice constants a = 18.0792(3) Å, b = 9.0626(2) Å, c = 10.0372(2) Å, beta = 112.107(1) degrees, and Z = 4; the final refinement of 52 variables converged to R(p)(), R(wp)(), R(F)(), and R(F)()()2 of 8.2, 10.8, 4.6, and 8.3%, respectively, for data collected between 4 and 60 degrees (2theta). At 50 K the phase is described by a triclinic unit cell, space group P&onemacr;, and is characterized by the lattice constants a = 9.8637(6) Å, b = 8.9290(6) Å, c = 9.8870(5) Å, alpha = 115.051(3) degrees, beta = 108.587(5) degrees, gamma = 92.015(5) degrees, and Z= 2; the final refinement of 102 variables converged to and R(p)(), R(wp)(), R(F)(), and R(F)()()2 of 8.3, 11.4, 1.5, and 3.0%, respectively, for data collected between 3 and 74 degrees (2theta). The transition between the two crystalline phases has been determined by differential scanning calorimetry to occur at circa 220 K, and the most pronounced difference in the environment of the chains, as determined by variable-temperature IR spectroscopy, is in the rho(PCH(3)) modes for the bridging dimethylphosphinate ligands.

We report the ab initio structure solutions of C(6)H(5)OM (M = K, Rb, Cs) by high-resolution powder X-ray diffraction. The compounds, which are of interest for reactions of the Kolbe-Schmitt type, are isostructural. The crystal structures are orthorhombic, space group Pna2(1), Z = 12, with lattice parameters (a, b, c in Å) 14.1003(1), 17.9121(1), and 7.16475(1) for the K compound, 14.4166(2), 18.2028(2), and 7.4009(1) for the Rb compound, and 14.8448(2), 18.5070(2), and 7.6306(1) for the Cs compound. They have a chain structure [M([6])] along the crystallographic c axis. This is a very unusual arrangement in which two different alkali-metal coordination spheres are observed: a distorted octahedron and a 3-fold oxygen coordination. In the latter, the 3-fold-coordinated unsaturated alkali metals additionally show weak interactions with phenyl rings. We also give powder patterns for the compounds with M = Li, Na. The former crystallizes in the monoclinic space group P2(1)/a with lattice parameters a = 22.594 Å, b = 4.7459 Å, c= 10.053 Å, and beta = 97.82 degrees with Z = 8, but no structure solution was possible. The powder pattern for the Na phenolate is in agreement with the earlier single-crystal structure.

In a process inhibited by the quinoline antimalarial drugs, Plasmodia detoxify heme released during the degradation of hemoglobin by aggregating it into malarial pigment, an insoluble crystalline heme coordination polymer. Synchrotron x-ray powder diffraction patterns for intact desiccated malarial trophozoites and synthetic beta-hematin have been measured; both materials correspond to a single crystalline triclinic lattice with unit cell parameters a = 12.2176(4), b = 14.7184(5), c = 8.0456(3) A; alpha = 90.200(2), beta = 96.806(3), gamma = 97.818(3) degrees and Z = 2. These results unambiguously demonstrate that hemozoin crystallites are identical to synthetic beta-hematin.