Laser-synthesized nanocrystalline, ferroelectric, bioactive BaTiO3/Pt/FS for bone implants.

The goal of our study is to design BaTiO3 ferroelectric layers that will cover metal implants and provide improved osseointegration. We synthesized ferroelectric BaTiO3 layers on Pt/fused silica substrates, and we studied their physical and bio-properties. BaTiO3 and Pt layers were prepared using KrF excimer laser ablation at substrate temperature Ts in the range from 200°C to 750°C in vacuum or under oxygen pressure of 10 Pa, 15 Pa, and 20 Pa. The BaTiO3/Pt and Pt layers adhered well to the substrates. BaTiO3 films of crystallite size 60-140 nm were fabricated. Ferroelectric loops were measured and ferroelectricity was also confirmed using Raman scattering measurements. Results of atomic force microscopy topology and the X-ray diffraction structure of the BaTiO3/Pt/fused silica multilayers are presented. The adhesion, viability, growth, and osteogenic differentiation of human osteoblast-like Saos-2 cells were also studied. On days 1, 3, and 7 after seeding, the lowest cell numbers were found on non-ferroelectric BaTiO3, while the values on ferroelectric BaTiO3, on non-annealed and annealed Pt interlayers, and on the control tissue culture polystyrene dishes and microscopic glass slides were similar, and were usually significantly higher than on non-ferroelectric BaTiO3. A similar trend was observed for the intensity of the fluorescence of alkaline phosphatase, a medium-term marker of osteogenic differentiation, and of osteocalcin, a late marker of osteogenic differentiation. At the same time, the cell viability, tested on day 1 after seeding, was very high on all tested samples, reaching 93-99%. Ferroelectric BaTiO3 films deposited on metallic bone implants through a Pt interlayer can therefore markedly improve the osseointegration of these implants in comparison with non-ferroelectric BaTiO3 films.

Order-disorder phase transition in the peroxidovanadium complex NH4[VO(O2)2(NH3)].

Complex NH4[VO(O2)2(NH3)] (1) undergoes an order-disorder phase transition at Tc~258K. This transition is accompanied by change in the space group of the orthorhombic lattice and also by significant structural rearrangements of the constituent molecules, which are pertinent mostly to their NH4+ ions and their ammonia ligands. The low-temperature solid state IR and Raman spectra of 1 were corroborated by solid-state computations that employed Gaussian functions as the basis set. Results of these computations yielded excellent agreement with experimental data. On the curves of temperature dependence of vibrational modes, the phase transition is expressed by an abrupt change of the slope above Tc.

PLD prepared bioactive BaTiO3 films on TiNb implants.

BaTiO3 (BTO) layers were deposited by pulsed laser deposition (PLD) on TiNb, Pt/TiNb, Si (100), and fused silica substrates using various deposition conditions. Polycrystalline BTO with sizes of crystallites in the range from 90nm to 160nm was obtained at elevated substrate temperatures of (600°C-700°C). With increasing deposition temperature above 700°C the formation of unwanted rutile phase prevented the growth of perovskite ferroelectric BTO. Concurrently, with decreasing substrate temperature below 500°C, amorphous films were formed. Post-deposition annealing of the amorphous deposits allowed obtaining perovskite BTO. Using a very thin Pt interlayer between the BTO films and TiNb substrate enabled high-temperature growth of preferentially oriented BTO. Raman spectroscopy and electrical characterization indicated polar ferroelectric behaviour of the BTO films.

Novel organic NLO material bis(N-phenylbiguanidium(1+)) oxalate - A combined X-ray diffraction, DSC and vibrational spectroscopic study of its unique polymorphism.

Three polymorphic modifications of bis(N-phenylbiguanidium(1+)) oxalate are reported, and their characterization is discussed in this paper. The non-centrosymmetric bis(N-phenylbiguanidium(1+)) oxalate (I), which was obtained from an aqueous solution at 313K, belongs to the monoclinic space group Cc (a=6.2560(2)Å, b=18.6920(3)Å, c=18.2980(5)Å, ß=96.249(1)°, V=2127.0(1)Å(3), Z=4, R=0.0314 for 4738 observed reflections). The centrosymmetric bis(N-phenylbiguanidium(1+)) oxalate (II) was obtained from an aqueous solution at 298K and belongs to the monoclinic space group P21/n (a=6.1335(3)Å, b=11.7862(6)Å, c=14.5962(8)Å, ß=95.728(2)°, V=1049.90(9)Å(3), Z=4, R=0.0420 for 2396 observed reflections). The cooling of the centrosymmetric phase (II) leads to the formation of bis(N-phenylbiguanidium(1+)) oxalate (III) (a=6.1083(2)Å, b=11.3178(5)Å, c=14.9947(5)Å, ß=93.151(2)°, V=1035.05(8)Å(3), Z=4, R=0.0345 for 2367 observed reflections and a temperature of 110K), which also belongs to the monoclinic space group P21/n. The crystal structures of the three characterized phases are generally based on layers of isolated N-phenylbiguanidium(1+) cations separated by oxalate anions and interconnected with them by several types of N-H(...)O hydrogen bonds. The observed phases generally differ not only in their crystal packing but also in the lengths and characteristics of their hydrogen bonds. The thermal behaviour of the prepared compounds was studied using the DSC method in the temperature range from 90K up to a temperature near the melting point of each crystal. The bis(N-phenylbiguanidium(1+)) oxalate (II) crystals exhibit weak reversible thermal effects on the DSC curve at 147K (heating run). Further investigation of this effect, which was assigned to the isostructural phase transformation, was performed using FTIR, Raman spectroscopy and X-ray diffraction analysis in a wide temperature range.

Pb2MnTeO6 Double Perovskite: An Antipolar Anti-ferromagnet.

Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ∼120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s(2) lone-pair electrons, together with a surprising off-centering of Mn(2+) (d(5)) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ∼150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6.

High- and low-temperature phases in isostructural 4-chloro-3-nitroaniline and 4-iodo-3-nitroaniline.

The structures of 4-chloro-3-nitroaniline, C6H5ClN2O2, (I), and 4-iodo-3-nitroaniline, C6H5IN2O2, (II), are isomorphs and both undergo continuous (second order) phase transitions at 237 and 200 K, respectively. The structures, as well as their phase transitions, have been studied by single-crystal X-ray diffraction, Raman spectroscopy and difference scanning calorimetry experiments. Both high-temperature phases (293 K) show disorder of the nitro substituents, which are inclined towards the benzene-ring planes at two different orientations. In the low-temperature phases (120 K), both inclination angles are well maintained, while the disorder is removed. Concomitantly, the b axis doubles with respect to the room-temperature cell. Each of the low-temperature phases of (I) and (II) contains two pairs of independent molecules, where the molecules in each pair are related by noncrystallographic inversion centres. The molecules within each pair have the same absolute value of the inclination angle. The Flack parameter of the low-temperature phases is very close to 0.5, indicating inversion twinning. This can be envisaged as stacking faults in the low-temperature phases. It seems that competition between the primary amine-nitro N-H···O hydrogen bonds which form three-centred hydrogen bonds is the reason for the disorder of the nitro groups, as well as for the phase transition in both (I) and (II). The backbones of the structures are formed by N-H···N hydrogen bonding of moderate strength which results in the graph-set motif C(3). This graph-set motif forms a zigzag chain parallel to the monoclinic b axis and is maintained in both the high- and the low-temperature structures. The primary amine groups are pyramidal, with similar geometric values in all four determinations. The high-temperature phase of (II) has been described previously [Garden et al. (2004). Acta Cryst. C60, o328-o330].

Structure determination of KLaS2, KPrS2, KEuS2, KGdS2, KLuS2, KYS2, RbYS2, NaLaS2 and crystal-chemical analysis of the group 1 and thallium(I) rare-earth sulfide series.

One of the purposes of this work is to provide a crystallographic review of group 1 and thallium rare-earth ternary sulfides M(+)Ln(3+)S2. We have therefore determined crystal structures of KLaS2, KPrS2, KEuS2, KGdS2, KLuS2, KYS2, RbYS2, which belong to the α-NaFeO2 structural family (R3m), as well as NaLaS2, which is derived from the disordered NaCl structural type (Fm3m). The determined structures were compared with known members of the group 1 as well as thallium(I) rare-earth sulfides by the standard tools of crystal-chemical analysis such as comparison of bond-valences, analysis of interatomic distances and comparison of the unit-cell parameters. The results indicate why the cubic structural type is limited to Li(+) and Na(+) members of the series only. The analysis has also revealed frequent problems in the reported crystal structures, especially in the determination of the K(+) compounds, probably due to severe absorption and different accuracy and sensitivity of various instruments. Intense diffuse scattering has been discovered in NaLaS2, which will be the subject of further investigation. The newly determined as well as already known structures are summarized, together with critical comments about possible errors in the previous structure determinations.

N-[Amino(imino)methyl]uronium tetrafluoroborate.

In the title compound, C(2)H(7)N(4)O(+)·BF(4) (-), inter-molecular N-H⋯O hydrogen bonds connect the cations into chains parallel to the c axis, with graph-set motif C(4). These chains are in turn connected into a three-dimensional network by inter-molecular N-H⋯F hydrogen bonds. The B-F distances distances in the anion are not equal.

A new modification of thallium chromate related to the beta-K2SO4 family.

The title structure is a new modification of Tl(2)CrO(4). There are four independent Tl(+) cations and two [CrO(4)](2-) anions in the structure. It is closely related to the already known modification, which belongs to the beta-K(2)SO(4) family with two independent cations and one anion. In both modifications, the cations and anions are situated on crystallographic mirror planes. The volume of the asymmetric unit of the title structure is approximately 0.4% smaller than that of the known modification belonging to the beta-K(2)SO(4) family. The other difference between the two modifications is seen in the environment of the cations. In the title structure, none of the Tl(+) cations is underbonded, in contrast with the modification isostructural with beta-K(2)SO(4). In the beta-K(2)SO(4) family with simple cations, underbonding of one of the constituent cations is typical. The dependence of the unit-cell parameters on temperature does not indicate a phase transition in the interval 90-300 K.

(Tetra-oxidoselenato-κO)tris-(thio-urea-κS)zinc(II).

The title structure, [Zn(SeO(4))(CH(4)N(2)S)(3)], is isomorphous with sulfatotris(thio-urea)zinc(II). In both structures, the Zn(2+) cation is coordinated in a tetra-hedral geometry. The corresponding intra-molecular distances are quite similar except for the Se-O and S-O distances. Although the hydrogen-bonding patterns are similar, there are some differences; in the title structure all the H atoms are involved in the hydrogen-bond pattern, in contrast to the situation in sulfatotris(thio-urea)zinc(II). No reproducible anomalies were detected by differential scanning calorimetry in the range 93-463 K until decomposition started at the higher temperature.

Dirubidium fluorotrioxophosphate, Rb2PO3F, at 290 and 130 K, and dicaesium fluorotrioxophosphate, Cs2PO3F, at 240 and 100 K.

The structure of Rb2PO3F was determined at 290 and 130 K, while that of Cs2PO3F was determined at 240 and 100 K. Both compounds belong to the beta-K2SO4 family. The structure analysis did not reveal signs of a phase transition in either compound. Crystal chemical considerations do not favour the presence of a phase transition in either Rb2PO3F or Cs2PO3F. However, glass-like phase transitions were observed by differential scanning calorimetry in slightly humid samples at 175 and 177 K for Rb2PO3F and Cs2PO3F, respectively, but were not observed in well dried samples. The bond distances are normal and Cs2PO3F is twinned.

Tris(methylammonium) hydrogenphosphate dihydrogenphosphate.

The title compound, 3CH6N+.HPO4(2-).H2PO4-, aggregates with the moieties interconnected by O-H...O and N-H...O hydrogen bonds, with O...O and N...O distances in the ranges 2.5366 (16)-2.5785 (14) and 2.7437 (16)-2.9967 (18) A, respectively. Three C-H...O hydrogen bonds are also present, with C...O distances in the range 3.2310 (18)-3.3345 (17) A. All H atoms are ordered. Structures with ordered hydrogenphosphate and dihydrogenphosphate components are rare.

Two phases of bis(tetraethylammonium) di-mu-chloro-bis[dichloropalladium(II)].

A phase transition was found to occur at approximately 153 K in the title compound, (C8H20N)2[PdCl6]. The structures of the two phases are reported at 292 and 130 K. The low-temperature phase is twinned. The phase transition is accompanied by a minor displacement of the ions. There are C-H...Cl interactions as short as approximately 2.80 A, indicating the existence of hydrogen bonds, and this was confirmed by vibrational spectroscopy. The [Pd2Cl6]2- anion occupies sites of mmm and 2/m symmetry in the room-temperature and low-temperature phases, respectively.

Two modifications of a KH2PO4.HF adduct.

The structures of two modifications, (I) and (II), of potassium dihydrogenphosphate-hydrofluoric acid (1/1), KH(2)PO(4).HF, were determined at 250 and 150 K, and at 292 and 150 K, respectively. Modifications (I) and (II) crystallize from stoichiometric aqueous solutions at 295 (1) and 308 (3) K, respectively. The H atoms were located clearly from the difference Fourier maps in each modification. The two modifications differ mainly in the arrangement of the dihydrogenphosphate anions, i.e. (I) contains looped dimeric and tetrameric units of the dihydrogenphosphate ions, whereas (II) contains two types of looped tetrameric unit. In addition, both structures contain a very short F-H.O hydrogen bond (2.38-2.40 A). The K(+) ions are coordinated by O and F atoms, with similar K.O and K.F distances in both modifications.

Bis(ammonium) fluorophosphate at room temperature.

The title room-temperature phase of (NH(4))(2)(PO(3)F) is orthorhombic (Pna2(1)) and is related to the beta-K(2)SO(4) structure family. The title structure consists of ammonium cations, NH(4)(+), and fluorophosphate anions, (PO(3)F)(2-). These ions are connected by N-H.O hydrogen bonds. Two-centre N-H.F hydrogen bonds are not present in the structure. Phase transitions were detected at 251+/-2 and 274+/-2 K during cooling and heating, respectively.