Volume 218, Issue 5

The average structures ( Immm ) of Gd 13 Br 18 B 3 ( A = 3.9923(2) Å, B = 17.0462(12) Å, C = 28.3039(19) Å) and Tb 13 Br 18 B 3 ( A = 3.9637(3) Å, B = 16.9063(13) Å, C = 28.1068(18) Å) were solved taking into account Bragg intensities only. The average structure contains an ordered honeycomb arrangement of chains formed from trans edge sharing Tb 6 B octahedra and disordered and partly occupied chains of double octahedra in the channels. Pronounced diffuse scattering which is elongated in [001]* indicates a 2D order of the structure. High resolution electron microscopy (HRTEM) gives insight into the nature of the ordering and leads to a model of discrete Tb 10 B 2 clusters in the channels which are perfectly ordered in layers in a 2 × 2 × 2 supercell. These layers are randomly stacked with well defined translation values to each other along [100].

X-ray single crystal, X-ray powder and specific heat investigations were carried out on alumosilicate NaNO 3 -sodalite between 290 K and 1100 K. Single crystal structure determinations at 295 K, 505 K and 720 K reveal the sodalite structure in its partially collapsed form in space group P 4̅3 n whereas at 935 K the z coordinate of the framework oxygen is shifted to z = 0.5 according to an untilted sodalite framework in Pm 3̅ n . The sodium ions are located on 8 e ( x, x, x ) position in P 4̅3 n and become statistically distributed on 16 i ( x, x, x ) in Pm 3̅ n . The displacements of the nitrate atoms are extraordinarily enlarged at 935 K compared to the values at the lower temperatures. Analysis of the X-ray powder data show a discontinuity in the thermal expansion behaviour at T c = 930 K with the temperature dependence of the lattice parameter described by a calc = a 1 — A ( T c — T ) 0.5 , a 1 = BT + a 0 ( A = 0:57 pm K –0.5 , B = 5:84 · 10 3 pm K –0.5 , a 0 = 909.9 pm, T in K) which is related to a square root decrease of the volume strain. The anomalous thermal expansion compromises a gradual contraction of TO 4 units and the disappearence of structural tilt with increasing temperature. The refined data reveal a change of z coordinate of O1 proportional to ( T c -T) 1/4 in P 4̅3 n which is considered as an effective order parameter in a Landau tricritical description of the phase transition triggered by the displacement of the cage filling ions.

A new dicobalt pyrophosphate, Co 2 P 2 O 7 ·6H 2 O, has been synthesized and characterized by single crystal X-ray diffraction. The compound belongs to the mono clinic space group P 2 1 / n , and its unit cell dimensions are: a = 7.2077(2), b = 18.3373(5), c = 7.6762(2) Å, β = 92.4356(15)°, V = 1013.64(5) Å 3 , Z = 4. The structural parameters were refined to an R index of 0.0570 for 1937 reflections with I >2 σ ( I o ). The framework of this pyro phosphate is made by the packing of layers of discrete CoO 6 octahedra connected by double tetrahedra P 2 O 7 groups. The (P 2 O 7 ) 4– anion group shows bent eclipsed conformation. A comparative study among anhydrous ( α -, β - and γ -Co 2 P 2 O 7 ) and hydrated forms (Co 2 P 2 O 7 ·2H 2 O) of dicobalt pyrophosphates known in literature is presented.

Crystals of Cu(OH)F and Cu 3 (OH) 2 F 4 have been synthesized at low-hydrothermal conditions in sizes up to 0.3 mm. The structures were solved from CCD X-ray single-crystal data and refined to R = 0.033 and 0.019, respectively. Cu(OH)F: space group P 2 1 / a , Z = 4, a = 5.301(1) Å, b = 6.376(1) Å, c = 5.074(1) Å, β = 112.90(1)°, and V = 157.98(5) Å 3 . Cu 3 (OH) 2 F 4 : space group P 2 1 / n , Z = 2, a = 5.501(1) Å, b = 4.766(1) Å, c = 8.462(1) Å, β = 92.28(1)°, and V = 221.68(7) Å 3 . In both compounds the copper atoms are 4 + 2 coordinated to their ligands ( Jahn-Teller distortion). Cu(OH)F is isotypic to Cu(OH)Cl, forming layers of edge-sharing Cu(OH) 3 F 3 polyhedra, which are interconnected by hydrogen bonds. The structure of Cu 3 (OH) 2 F 4 is characterized by chains of edge-sharing Cu(OH) 2 F 4 polyhedra running along [1 0 0], which are linked to each other via corners to form a framework. Hydrogen bonds of the type O—H···F occur with O···F distances of 2.619 and 2.697 Å in Cu(OH)F and Cu 3 (OH) 2 F 4 , respectively. The observed O—H stretching frequencies of 3129 and 3306 cm –1 , respectively, in Raman spectra are in excellent agreement with expected values from distance — frequency correlations. Moreover, the pleochroism of the bands corresponds in both compounds to the O—H orientation found in the structure determination.

Crystals of three Pb oxide phosphates, Pb 4 O(PO 4 ) 2 , Pb 8 O 5 (PO 4 ) 2 and Pb 10 (PO 4 ) 6 O, were synthesized from mixtures of PbO and NH 4 H 2 PO 4 heated to 950 °C. The crystal structure of Pb 4 O(PO 4 ) 2 (monoclinic, P 2 1 / c , a = 9.4894(8), b = 7.1402(6), c = 14.4077(13) Å, β = 104.549(2)°, V = 944.91(14) Å 3 ) was solved by direct methods and refined to R 1 = 0.044 ( wR = 0.103). It contains isolated OPb 4 tetrahedra that are linked through Pb—O bonds to O atoms of PO 4 tetrahedra. The crystal structure of Pb 8 O 5 (PO 4 ) 2 (monoclinic, C 2/ m , a = 10.6427(4), b = 10.2078(4), c = 14.3530(6) Å, β = 98.325(1)°, V = 1542.86(11) Å 3 ) was solved by direct methods and refined to R 1 = 0.032 ( wR = 0.068). It is based upon a complex sheet with composition [O 5 Pb 8 ]. The basic element of the sheet is a cluster of composition [O 5 Pb 10 ] that consists of four OPb 4 tetrahedra that share edges. The adjacent [O 5 Pb 10 ] clusters are linked by sharing Pb atoms, resulting in sheets that are parallel to (001). The PO 4 tetrahedra are located in the interlayers between the sheets. The crystal structure of Pb 10 (PO 4 ) 6 O (hexagonal, P 6 3 / m , a = 9.8650(3), c = 7.4306(3) Å, V = 626.25(4) Å 3 ) has been solved by direct methods and refined to R 1 = 0.040 ( wR = 0.106). Pb 10 (PO 4 ) 6 O crystallizes with an apatite-type structure. The structure contains a single O atom that is not part of a PO 4 tetrahedron; it has a site occupancy factor of 0.25 and is located on the 6 3 axis.

The effect of cooling down to 150 K on the structures of α - (s.g. P 2 1 / n ), β - (s.g. P 2 1 ), and γ - (s.g. P 3 1 ) polymorphs of glycine was studied by X-ray single-crystal diffraction. No polymorphic transformations were detected. Relative volume changes and the anisotropy of structural distortion of the three polymorphs of glycine were compared. Maximum contraction of structures was measured in the b -direction for the α - and β -polymorphs, and in the a -direction for the γ -polymorph. Minimum contraction in the γ -polymorph was measured in c -direction. The structures of the α - and the β -polymorphs slightly expanded on cooling in the directions close to c . The directions of maximum and minimum lattice strain were related to the directions of weak and strong hydrogen bonds in the structures. Crystal structures for the three polymorphs were refined at 294 K and at 150 K. The effects of cooling on the intramolecular geometry of glycine molecules and on the intermolecular hydrogen bonds in all the three polymorphs were compared. Structural distortion on cooling was compared with that on increasing hydrostatic pressure.

The structure of the organic derivative of N-p-methylbenzyliden-N-phenyl-p,p′-dimethoxybenzoyl acetic acid hydrazide, [C 32 H 28 N 2 O 5 ], has been determined by X-ray diffraction. The structure derived from the NMR spectroscopy, the IR spectra and elemental analysis is consistent with that of the X-ray diffraction. The compound crystalizes in the monoclinic system with space group P 21/ c , a = 16.234(1), b = 9.399(2), c = 19.389(1), β = 110.924(3)°, V = 2763.3(5) Å 3 and Z = 4. In the crystal, there is one weak C—H…O type intermolecular hydrogen bond interaction.

A new type of inclusion complex, S(–)-1 phenyl ethyl ammonium percholorate complex of R-(–)-2-ethyl - N - benzyl - 4, 7, 10, 13 - tetraoxa -1- azacyclopentadecane, has been prepared and studied by NMR, IR and single crystal X-ray diffraction techniques. The compound crystallizes in space group P 2 1 with cell dimensions a = 10.0000(8), b = 12.281(2), c = 12.331(1)Å, β = 102.052(7), Z = 2 The host-guest complex is held together by a strong system of hydrogen bonds between the two protons of the ammonium ion as well as the nitrogen and four oxygen atoms of the crown ether The C—O and C—C distances of the 15-membered ring average 1.418 and 1.501 Å while the O—C—C and C—O—C angles average 110.2 and 113.3°. The average N—C distance is 1.476 Å.

The molecular structure of the title complex [ZnCl 2 (C 7 H 6 N 2 ) 2 ] was investigated by X-ray diffraction and IR spectroscopy. The Zn(II) complex crystallizes triclinically ( P 1̅ (no 2); a = 7.440(2) Å, b = 7.734(2) Å, c = 13.3127(4) Å, α = 85.91(2)°, β = 85.97(2)°, γ = 83.05(5)°, Z = 3; V = 757.3(3) Å 3 ). In the molecular structure, the Zn atom is coordinated tetrahedrally by two Cl – anions and two benzimidazole ligands.