Athos Callegari

Structure and solid-state chemistry of anhydrous and hydrated crystal forms of the trimethoprim-sulfamethoxypyridazine 1:1 molecular complex

The crystal structure of the equimolar trimethoprim (TMP) and sulfamethoxypyridazine (SMPD) complex in the anhydrous form (TMP. SMPD) and that of the species with 1.5 molecules of water of crystallization (TMP.SMPD.W) are reported in this article. X-ray powder diffraction patterns (both computer generated and experimental) and thermal analytical data from differential scanning calorimetry (DSC) and thermogravimetry useful for the characterization of TMP.SMPD and TMP.SMPD.W are provided. The stability of TMP.SMPD.W, which retains its crystallographic order under 0% relative humidity (RH) conditions at room temperature (22 degrees C) and 20 mmHg, is accounted for in terms of crystal structure and hydrogen bonding. Transformation of TMP.SMPD to the hydrate complex by exposure to approximately 100% RH, suspension in water, and wet granulation, and dehydration of TMP.SMPD.W by thermal treatment and by desiccation with methanol were investigated and tentatively interpreted in terms of crystal properties. Interactions in the physical mixture of TMP and SMPD by grinding, compression, heating, and contact with water were also studied. Water-mediated formation of TMP.SMPD.W by wetting and metastable eutectic melting-mediated formation of TMP.SMPD by heating was demonstrated. Mechanical activation by milling makes the physical mixture prone to solid-state transformation into dimorphic anhydrous cocrystals by supply of thermal energy during a DSC scan.

The crystal structure of peprossiite-(Ce), an anhydrous REE and Al mica-like borate with square-pyramidal coordination for Al

Abstract Single-crystal structure refinements are presented of the holotype of crystal peprossiite-(Ce) (Monte Cavalluccio) and of a new sample from Cura di Vetralla (Viterbo, Italy) with slightly different composition, together with new EMP-SIMS chemical analyses. These results allow us to propose a new unit formula: [REE1-x-y(Th,U)xCay](Al3O)2/3[(B4-zSiz)]O10 with x - y + z = 1/3 (Z = 1) for the peprossiite group. Lattice constants for the holotype crystal are: a = 4.612(1), c = 9.374(3) Å, V = 172.6 Å3, Z = 1, space group P6̅ 2m. The crystal structure was solved by Patterson methods and refined to Robs = 1.8% (Rall = 2.2%) for 706 unique reflections in the 2q-range 6-136°. Lattice constants for the thorian peprossiite-(Ce) from Cura di Vetralla are: a = 4.596(3), c = 9.309(16) Å, V = 170.3 Å3, and the structure was refined to Robs = 2.9% and Rall = 3.0% for 271 unique reflections in the 2θ-range 4-80°. The topology of the tetrahedral layer and the site of the inter-layer cation (REE) in peprossiite resembles that of dioctahedral micas. The main difference lies in the presence of layers of pyramids instead of layers of octahedra typical of mica. In peprossiite, Al is coordinated by five O atoms in a nearly square-pyramidal arrangement, the base of which is formed by pairs of apical O atoms from two layers of tetrahedra related by a mirror plane. Three of these pyramids share their apical O forming Al3O groups with occupancy of 2/3 according to the structure refinement. A model is proposed that explains the apparent disorder in the pyramidal layer of peprossiite by the stacking within a triple cell (with a′ = a √ 3 and a ^ a′ = 30°) of three ordered layers randomly translated by ± a.

Origin of prismatine from the Sondalo granulites (Central Alps, northern Italy)

A granulite from the Sondalo femic complex, Italian Central Alps, contains prismatine, the boron-rich member of the kornerupine group. This is the first report of prismatine in the Alps. The granulite consists of albite-rich plagioclase + cordierite + sillimanite + rutile + hercynite + corundum + quartz and is interpreted as a restite formed after partial melting of amphibolite-facies tourmaline-bearing metasediments at about 900°C and 0.8 GPa. Prismatine grains, which form a coarse aggregate with tourmaline, biotite and albitic plagioclase, have inclusions of sapphirine, hercynite and corundum. Secondary-ion mass spectrometry (SIMS) analyses on prismatine gives B 2 O 3 = 2.30–2.89 wt.%, Li 2 O = 0.067–0.125 wt.%, BeO = 0.005–0.007 wt. %, F = 0.32–0.49 wt. % and H 2 O = 0.90–1.02 wt.%. The cell parameters a and c and V of the Sondalo prismatine fit with the B 2 O 3 co-variation reported in literature. We propose a mechanism of prismatine formation involving the breakdown of tourmaline during the anatexis of the amphibolite-facies metasediments and the development of prismatine as a refractory phase. No intervention of a metaso-matic boron-rich fluid is required. The possible tourmaline breakdown process is the reaction 7.82 tourmaline + 1.03 biotite + 2.41 sapphirine + 3.22 quartz = 8.00 prismatine + 5.93 melt + 1 B 2 O 3 .

Modular aspects of the crystal structures of kurchatovite and clinokurchatovite

The crystal structures of the two polytypes of the compound CaMgB 2 O 5 , kurchatovite and clinokurchatovite, were determined in the space groups Pc2 1 b and P2 1 /c respectively by Yakubovich et al. (1976) and Simonov et al. (1980). The crystal structures of both minerals have been re-examined and refined until R obs = 3.00 and 2.82%. The lattice parameters are for kurchatovite a = 36.34,b= 11.135,c = 5.499 A, Z = 24, space group Pbca, and for clinokurchatovite a = 12.329,b = 11.146,c = 5.519 A, s = 101.62°, Z = 8, space group P2 1 /c. Common features of both structures are the B 2 O 5 clusters formed by two B-triangles with a common vertex, the Mg-octahedra and Ca-polyhedra with seven corners. The two crystal structures show very close similiarities, both being based on the repeat of a monoclinic module, whose volume is one fourth of that of the unit cell of clinokurchatovite (a 0 = a/4). The possibility of further structures based on the same module is discussed.

The crystal structure of vicanite-(Ce), a borosilicate showing an unusual (Si3B3O18)15− polyanion

Abstract The crystal structure of holotype vicanite-(Ce) has been solved and refined to R = 1.8% for 1398 observed reflections with the aid of a new crystal from the same locality (Tre Croci, Vetralla, Italy), found more than 10 years after the first. The new unit formula is (Ca,REE,Th)15Fe3+(SiO4)3 (Si3B3O18)(BO3)(As5+O4)(As3+O3)x(NaF3)1-xF7·0.2H2O with x = 0.4. The structure is trigonal, R3m, Z = 3, a = 10.8112(2), c = 27.3296(12) Å, and layered along [001] with three distinct layers. Layer A at z ca. 0 (1/3, 2/3) contains an Fe(SiO4)6 group and a threefold B3O9 borate ring. Each tetrahedron of the ring shares one oxygen atom with one Si tetrahedron, forming an unusual Si3B3O1815- polyanion. Layer B at z ca. 1/9 (4/9, 7/9) contains an AsO4 tetrahedron and a BO3 triangle. Layer C at z ca. 2/9 (5/9, 8/9) represents the disordered part of the structure, containing two very close (0.85 Å) As3+O33- and NaF32- polyhedra, the occurrence of which is mutually exclusive and statistically disordered. A 3-dimensional network of M-(O,F)n polyhedra (M = Ca, REE, Th; 8 < n < 10) provide connections among neighboring layers.

The crystal structure of piergorite-(Ce), Ca8Ce2(Al0.5 Fe0.53+)∑1(□,Li,Be)2Si6B8O36(OH,F)2: A new borosilicate from Vetralla, Italy, with a modified hellandite-type chain

Abstract Piergorite-(Ce) is a new mineral found at Tre Croci, Vetralla, Italy with simplified formula Ca8Ce2 (Al0.5Fe3+ 0.5)Σ1(□,Li,Be)2Si6B8O36(OH,F)2. It occurs as strong intergrowths of small crystals, colorless to pale yellow, associated with sanidine, mica, magnetite, rutile, titanite, and other Th-U-REE bearing minerals, in miarolitic cavities of a syenitic ejectum. Piergorite-(Ce) is biaxial negative, nα = 1.717 (1), nβ = 1.728 (1), and nγ = 1.735 (1), 2Vmeas = 68(2)°, X = b, and Z ^ c = 7(1)°. Crystals show tabular habit and a very good {010} cleavage; twinning along the (301̄) plane produces “L” forms. The three strongest lines in the simulated powder diffraction pattern (dobs, I, hkl) are: 2.65 Å, 100.0, (213, 4̄13); 1.91 Å, 48.3, (223, 4̄23, 821); 2.90 Å, 44.9, (6̄03, 6̄12). The structure was solved by Patterson synthesis from X-ray diffraction data [monoclinic, space group P2/a, a = 28.097(3) Å, b = 4.777(1) Å, c = 10.236(2) Å, β = 96.81(1)°, V = 1364.2(7) Å3, Z = 2] and was refined to a final Robs = 0.059 for 6480 Fo with Io > 3σ(Io). The structure shows similarities with the hellandite group because Si and B tetrahedra form chains along c. Hellandite structure is characterized by a single chain of five-membered rings, whereas piergorite-(Ce) shows a double chain of five-membered rings interconnected by a single octahedral site to form a three-dimensional framework containing five independent eightfold-coordinated M sites and a partly occupied T-cavity.

Thermal expansion of alunite up to dehydroxylation and collapse of the crystal structure

Abstract The high-temperature (HT) behaviour of a sample of natural alunite was investigated by means of in situ HT single-crystal X-ray diffraction from room temperature up to the dehydroxylation temperature and consequent collapse of the crystal structure. In the temperature range 25-500°C, alunite expands anisotropically, with most of the contribution to volume dilatation being produced by expansion in the c direction. The thermal expansion coefficients determined over the temperature range investigated are: αa = 0.61(2) × 10-5 K-1 (R2 = 0.988), αc = 4.20(7) × 10-5 K-1 (R2 = 0.996), αc /αa = 6.89, αV = 5.45(7) × 10-5 K-1 (R2 = 0.998). At ∼275-300°C, a minor discontinuity in the variation of unit-cell parameters with temperature is observed and interpreted on the basis of loss of H3O+ that partially substitutes for K+ at the monovalent A site in the alunite structure. Increasing temperature causes the Al(O,OH)6 sheets, which remain almost unaltered along the basal plane, to move further apart, and this results in an expansion of the coordination polyhedron around the intercalated potassium cation. Sulfate tetrahedra act as nearly rigid units, they contract a little in the lower temperature range to accommodate the elongation of the Al octahedra.

The chemistry and crystal structure of okanoganite-(Y) and comparison with vicanite-(Ce)

Abstract The structure of okanoganite-(Y), a rare REE-rich borofluorosilicate, was refined in space group R3m, starting from the atomic coordinates of vicanite-(Ce), to a final R-factor of 0.032 for 1857 observed reflections. Okanoganite-(Y) is trigonal with a = 10.7108(5), c = 27.0398(11) Å, Z = 3. SIMS procedures were used for the analysis of H, F, Li, Be, B, REE, Y, actinides (U, Th, Pb), and other trace elements (Sr, Ba, Cs). An excellent agreement was obtained by comparing EMPA + SIMS with SREF data. On the basis of 38 O atoms, the resulting unit formula is (Y4.52REE6.82Ca2.65Na1.63Th0.19Sr 0.02Ba0.01U0.01)Σ15.85(Fe3+0.74Ti0.19Li0.04)Σ0.97(Si6.71P0.32B2.94Be0.01)Σ9.98(O34.02OH3.98)Σ38F10.04. The chemical data are compared to those in the literature and discrepancies are discussed. The structure of okanoganite-(Y) resembles that of vicanite-(Ce). They are the only two borosilicates showing a structural unit of threefold rings of BO4 tetrahedra. The main differences between the two minerals lie in the different chemical composition [absence of As and low amount of Ca and Th in okanoganite-(Y); absence of Y and low amount of Na in vicanite-(Ce)] and in the lack, in okanoganite-(Y), of a B atom that is at the center of a triangular BO3 coordination in vicanite-(Ce). Additional analogies and differences between the two structures are shown.

Chemical and biological profile of racemic and optically active dialkylaminoalkylnaphthalenes with analgesic activity

The racemic mixtures and the enantiomers of dialkylaminoalkylnaphthalenes are described here as novel analgesic agents with potencies similar, or superior to that of morphine. The synthesis and isolation of the pure enantiomers and a study of the absolute configuration are reported. The resolution of racemates was accomplished by preparative liquid chromatography using a Chiralpak AD column. The configurational assignment was performed on the basis of the X-ray crystallographic analysis of (+)-benzyl-(3-hydroxy-3-naphthalen-2-yl-butyl)dimethylammonium bromide and by comparative study of CD and NOESY 1 H NMR spectra of the resolved enantiomers. Pharmacological evaluation of the analgesic activity by means of the hot plate test is described.

Aschamalmite (Pb6Bi2S9): crystal structure and ordering scheme for Pb and Bi atoms

Abstract The first single-crystal structure refinement of aschamalmite (Pb6Bi2S9) from Susa Valley (Piedmont, Italy) is reported. The mineral is monoclinic, C2/m, a = 13.719(1) Å, b = 4.132(1) Å, c = 31.419(3) Å, β = 90.94(1)°, V = 1 780.8(4) Å3, Z = 4. The Pb6Bi2S9 compound crystallizes also in an orthorhombic form as heyrovskyite (Cmcm) and our study is focused on understanding the reason leading to a change in symmetry. The aschamalmite structure forms because of ordering between Pb and Bi on the margins of the two octahedral layers that are symmetrically equivalent in heyrovskyite. The two alternate set of octahedral slabs are not related by a crystallographic mirror plane and the symmetry decreases to monoclinic. The cation ordering couples opposite sequences of Pb and Bi octahedra at the margins of slabs. In particular, the succession [Me4A]Bi-[Me5A]Pb-[Me4A]Bi-[Me5A]Pb faced to the series[Me4B]Pb-[Me5B]Bi-[Me4B]Pb-[Me5B]Bi occurs in about 70% of the unit-cells of the crystal, while the contrary sequence ([Me4A]Pb-[Me5A]Bi-[Me4A]Pb-[Me5A]Bi faced to [Me4B]Bi-[Me5B]Pb-[Me4B]Bi-[Me5B]Pb) occurs in the remaining unit-cells. The marginal octahedra have ideal populations (a.p.f.u.): [Me4A]1.40Bi+0.60Pb, [Me4B]1.40Pb+0.60Bi, [Me5A]1.40Pb+0.60Bi,[Me5B]1.40Bi+0.60Pb, in agreement with our structure-refinement results. The probable site populations for pure heyrovskyite have been proposed, as well as the reasons that prevent the formation of a completely ordered monoclinic phase.