Crystal Structure of Synthetic Mg-Whitlockite, Ca18Mg2H2(PO4)14

1974 ◽  
Vol 52 (7) ◽  
pp. 1155-1164 ◽  
Author(s):  
Ramanathan Gopal ◽  
Crispin Calvo ◽  
Jun Ito ◽  
W. K. Sabine
Keyword(s):  
Crystal Structure ◽  
Oxygen Atom ◽  
Least Squares ◽  
Formula Unit ◽  
Full Matrix ◽  
Space Group ◽  
R Value ◽  
Unit Density ◽  
A Chain ◽  
Automatic Diffractometer

Crystals of synthetic Mg-whitlockite, Ca18Mg2H2(PO4)14, have been grown by hydrothermal techniques and their structure refined by full-matrix least-squares methods, using 1626 unique reflections measured with a Syntex [Formula: see text] automatic diffractometer, to a final R value of 0.046. The crystals have space group R3c with ZR = 1, a = 13.765(8) Å and α = 44.25(5)° with the equivalent hexagonal parameters a = 10.350(5), c = 37.085(12) Å and ZH = 3. The structure, although similar to that of βCa3(PO4)2, differs significantly. The structure contains interconnected infinite chains of polyhedra paralleling the hexagonal c axis with links in the chains consisting of three CaO8 polyhedra separated by two PO4 tetrahedra. Six of these chains surround a chain of MgO6 octahedra and PO4H groups which lie on the three-fold axes. These chains however contain only half the formula unit density of the calcium containing ones and a proton, presumably disordered, is attached to the oxygen atom on the triad axes.

Refinement of the structure of Mg2As2O7

1970 ◽  
Vol 48 (6) ◽  
pp. 890-894 ◽  
Author(s):  
C. Calvo ◽  
K. Neelakantan
Keyword(s):  
Crystal Structure ◽  
Oxygen Atom ◽  
Least Squares ◽  
Unit Cell ◽  
Full Matrix ◽  
Space Group ◽  
Cell Dimensions ◽  
Central Oxygen ◽  
R Value ◽  
Unit Cell Dimensions

The crystal structure of Mg2As2O7 has been refined by full matrix least squares procedures using 587 observed reflections. The structure of Mg2As2O7 is of the thortveitite type, as reported by Łukaszewicz, with space group C2/m and unit cell dimensions a = 6.567(2) Å, b = 8.524(4) Å, c = 4.739(1) Å, β = 103.8(1)°, and Z = 2. The As—O—As group in the anion appears to be linear but the central oxygen atom undergoes considerable disorder in the plane perpendicular to this group. The AsO bond distances uncorrected for thermal motion are 1.67 Å for the As—O(—As) bond and 1.66 and 1.65 Å for the terminal As—O bonds. The final R value obtained is 0.088.

Crystal Structure of α-VPO5

1973 ◽  
Vol 51 (16) ◽  
pp. 2621-2625 ◽  
Author(s):  
Byron Jordan ◽  
Crispin Calvo
Keyword(s):  
Crystal Structure ◽  
Oxygen Atom ◽  
Least Squares ◽  
Least Squares Method ◽  
Fold Axis ◽  
Full Matrix ◽  
Bond Lengths ◽  
R Value ◽  
A Site ◽  
Vanadium Ion

α-VPO5 crystallizes in the tetragonal space group P4/n with a = 6.014(7) and c = 4.434(2) Å. The structure, isotypic with that of α-VSO5, was refined by full-matrix least-squares method to an R value of 0.089 using 239 independent reflections. The vanadium ion lies on a crystallographic four-fold axis, as does one of the oxygen atoms, and the P on a site of [Formula: see text] symmetry. A second oxygen atom, as a result of disorder, occurs in two positions which are mirror reflected with respect to the ac plane. The structure consists of highly distorted VO6 groups with bond lengths along the c axis of 1.580(11) and 2.853(11) Å while the remaining four V—O bond lengths are all 1.858(8) Å. The P—O bond lengths in the PO4. tetrahedron are 1.541(8) Å with the PO4 groups bridging across four chains of VO6 groups.

The Structure of Na4P2O7 at 22 °C

1972 ◽  
Vol 50 (16) ◽  
pp. 2519-2526 ◽  
Author(s):  
K. Y. Leung ◽  
C. Calvo
Keyword(s):  
Least Squares ◽  
Room Temperature ◽  
Orthorhombic Space Group ◽  
Full Matrix ◽  
Space Group ◽  
Bond Lengths ◽  
R Value ◽  
Automatic Diffractometer ◽  
Oxygen Atoms

At room temperature Na4P2O7 crystallizes in the orthorhombic space group P212121 with a = 9.367(5), b = 5.390(2), c = 13.480(8) Å, and z = 4. The structure was refined by full-matrix least-squares using 1337 reflections measured with a Syntex Automatic diffractometer. The final R value is 0.022. The anion has nearly an eclipsed configuration with a P—O—P angle of 127.5(1)°. The two bridging P—O bond lengths are 1.631(2) and 1.642(2) Å with terminal P—O bond lengths averages of 1.512 and 1.514 Å on either side of the anion. Two of the four Na+ ions are coordinated to five oxygen atoms while the remainder are coordinated to six oxygen atoms. The structure contains chains of cations with four nearly collinear Na+ per cell paralleling the c axis. These are surrounded by six anions with the bridging oxygen atoms lying approximately at the corners of an octahedron with the P—P vector of the anion also paralleling the c axis. Adjacent anions along the c axis are separated by a pair of Na+ ions.

The Structure of Thiobinupharidine

1973 ◽  
Vol 51 (17) ◽  
pp. 2810-2820 ◽  
Author(s):  
J. T. Wróbel ◽  
B. Bobeszko ◽  
T. I. Martin ◽  
D. B. MacLean ◽  
N. Krishnamachari ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Least Squares ◽  
Absolute Configuration ◽  
Spectroscopic Properties ◽  
Relative Configuration ◽  
Full Matrix ◽  
Space Group ◽  
R Value ◽  
Least Squares Techniques

The spectroscopic properties of thiobinupharidine and its isomer, neothiobinupharidine, of established structure, have been examined and compared. From this study it was possible to deduce the structure and relative configuration of the alkaloid. The structure has been firmly established and the absolute configuration determined by the study of the crystal structure of thiobinupharidine dihydrobromide dihydrate, C30H42O2N2S•2HBr•2H2O. The crystals are orthorhombic with space group C2221, a = 25.128(6), b = 9.869(2), c = 26.380(6) Å, and Z = 8. The structure was refined, using full-matrix least-squares techniques with 1934 reflections, to a final R value of 0.097. The thiobinupharidine moiety hydrogen bonds to one of two types of H2O–Br–H2O spiral chains in the structure. The tetrahydrothiophene ring is distorted from planarity, and this together with the nonequivalence of the S and C atoms in the ring causes the molecule to deviate from C2 symmetry

Refinement of the Crystal Structure of the Low-quartz Modification of Ferric Phosphate

1975 ◽  
Vol 53 (14) ◽  
pp. 2064-2067 ◽  
Author(s):  
Hok Nam Ng ◽  
Crispin Calvo
Keyword(s):  
Crystal Structure ◽  
Least Squares ◽  
Room Temperature ◽  
Unit Cell ◽  
Full Matrix ◽  
Space Group ◽  
Ferric Phosphate ◽  
R Value

The structure of ferric phosphate at room temperature was refined on a Dauphiné-twinned crystal using full-matrix least-squares methods. The final R value was 0.078 for 487 symmetry-independent reflections whose intensities were corrected for twinning. The structure was found to be isotypic with AlPO4 (berlinite) with the space group P3121 and four formula units in a unit cell defined by a = 5.036(2) and c = 11.255(4) Å. The structure is also closely related to that of α-quartz with a nearly doubled c-axis because of the ordering of Fe and P atoms. The PO4 tetrahedron is almost regular with a mean P—O distance of 1.526 Å. The Fe3+ ion is tetrahedrally coordinated with an average Fe—O distance of 1.853 Å.

Crystal Structure of Tetraethylammonium Bromopentacarbonyltungstate(0)

1995 ◽  
Vol 48 (5) ◽  
pp. 1045 ◽  
Author(s):  
T Whyte ◽  
GA Williams
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Least Squares ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
Space Group ◽  
X Ray ◽  
Bond Lengths ◽  
R Value

The crystal structure of tetraethylammonium bromopentacarbonyltungstate (0), [NEt4] [W(CO)5Br], has been determined by single-crystal X-ray diffraction methods at 22�1°C. Crystals are tetragonal, space group P4/n, with a 9.206(2), c 10.484(2) Ǻ, and Z 2. Full-matrix least-squares refinement gave a final R value of 0.034 for 820 independent reflections. The [W(CO)5Br]- anion possesses exact C4v symmetry, with bond lengths W-Br 2.736(1), W-COtrans 1.93(1) and W-COcis 2.034(6) Ǻ.

Crystal structure of N,N′-dimethyl-2-imidazolidinethione, a by-product from the reaction of Na2(CH2N(CH3)CS2)2 and HgCl2

1983 ◽  
Vol 61 (1) ◽  
pp. 211-213 ◽  
Author(s):  
Chung Chieh ◽  
Sing Kwen Cheung
Keyword(s):  
Crystal Structure ◽  
Bond Length ◽  
Least Squares ◽  
Aqueous Ethanol ◽  
Ethanol Solution ◽  
Aqueous Ethanol Solution ◽  
Hydrogen Atoms ◽  
Full Matrix ◽  
Space Group ◽  
Automatic Diffractometer

The reaction between mercury (II) chloride and N,N′-dimethylethylenebisdithiocarbamate gave a white precipitate. In an attempted recrystallization from an aqueous–ethanol solution, a cyclic thiourea-type compound, N,N′-dimethyl-2-imidazolidinethione, was obtained. The crystals of this compound are monoclinic, a = 10.388(2), b = 6.139(1), c = 12.291(4) Å, β = 118.64(2), and space group P21/c. The non-hydrogen atoms of the molecule are planar and the C=S bond length is 1.673(4) Å. The structure was refined by full-matrix least-squares from 642 independent reflections measured on an automatic diffractometer to R and Rw of 0.053 and 0.068, respectively.

Crystal Structure of the Glaserite Form of BaNaPO4

1975 ◽  
Vol 53 (12) ◽  
pp. 1849-1853 ◽  
Author(s):  
Crispin Calvo ◽  
Romolo Faggiani
Keyword(s):  
Crystal Structure ◽  
Bond Length ◽  
Least Squares ◽  
Coordination Number ◽  
Cation Site ◽  
Full Matrix ◽  
Space Group ◽  
Bond Lengths ◽  
R Value ◽  
Cation Sites

Crystals of BaNaPO4 were grown from a Ba3P2O8–Na2B4O7 melt. The crystals are trigonal, space group [Formula: see text]with a = 5.622(4) and c = 7.259(5) Å. The structure, isotypic with that of glaserite, was refined by full-matrix least-squares methods to a final R value of 0.042 using 218 unique reflections. There are three different cation sites. Na and Ba lie at sites of [Formula: see text] symmetry and are coordinated to 6 and 12 oxygen atoms respectively. The Na—O bond lengths are 2.344(7) Å and the two unique Ba—O bond lengths are 2.788(7) and 3.247(9) Å. The remaining cation site has 3m symmetry, a coordination number of 10, and contains equal amounts of Na+ and Ba2+. The bond lengths range from 2.548(12) to 3.017(7) Å. The phosphate group also has 3m symmetry with mean P—O bond lengths of 1.538 Å. The underbonded apical P—O bond length is 1.520 Å.

Synthesis, Properties and Crystal Structure Determination of a Perchloroheptafulvalene Isomer

1985 ◽  
Vol 38 (3) ◽  
pp. 383 ◽  
Author(s):  
HM Hugel ◽  
E Horn ◽  
MR Snow
Keyword(s):  
Crystal Structure ◽  
Least Squares ◽  
Structure Analysis ◽  
Lithium Chloride ◽  
Structure Determination ◽  
Full Matrix ◽  
Space Group ◽  
Synthesis Properties ◽  
R Value

Crystals of the syn-perchloroheptafulvalene isomer, C14Cl12, crystallize in the space group C2/c with a 12.376(6), b 10.980(4), c 15.242(4)Ǻ and β 100.54(3)°. The structure analysis of the isomer indicates molecular packing disorder into two orientations about the centre of symmetry. In the final full-matrix least-squares refinement the conventional R value converged at 0.042. Formation of the syn isomer is most likely to proceed through the perchloroheptatrienyl anion which can dimerize and form syn-perchloroheptafulvalene by cis elimination of lithium chloride.

Coordinated fluoride in rhenium(I) carbonyl complexes

1984 ◽  
Vol 37 (1) ◽  
pp. 35 ◽  
Author(s):  
E Horn ◽  
MR Snow
Keyword(s):  
Hydrogen Bonding ◽  
Least Squares ◽  
Mass Spectra ◽  
Structural Data ◽  
Monoclinic Space Group ◽  
Carbonyl Complexes ◽  
Full Matrix ◽  
Space Group ◽  
Corrected Data ◽  
R Value

Bromide abstraction from the complexes Re(CO)3L2Br (where L = SbPh3 and L2 = bpy, dpe, tmen)* by AgF2H gives the corresponding fluoro compounds Re(CO)3L2F. Mass spectra and structural data show that the fluoride in these complexes is coordinated to the metal. The structures of Re(CO)3(tmen)F and [Re(CO)3(tmen)F]2H.HOBF3 are reported here. Crystals of Re(CO)3(tmen)F are monoclinic, space group P21/c, with a 8.202(2), b 13.115(9), c 12.048(4) � and β 102 24(3)�. A full-matrix least-squares refinement by using the absorption corrected data gave a conventional R value of 0.041. [Re(CO)3(tmen)F]2H.HOBF3 also crystallizes in the space group P21/c. The lattice parameters are: a 17.495(2), b 10.772(2), c 15.447(1) � and β ( 101.409(8)�. The final R value of a blocked least-squares calculation converged at 0.061. In these two complexes the simple Re-F distance is 2.040(4) �, in Re(CO)3(tmen)F. The Re-F distance is increased to 2.236(10)�, as a result of hydrogen bonding between the fluoride and HOBF3 in the latter compound.

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