PubMed Health⌕ Search

Biomedical subjects

P S Halasyamani

Publications and source records attributed to P S Halasyamani.

6 recordsLinked to original sources
PubMed2001

Polar compounds constructed with the [Cr2O7]2- anion.

Crystalline KTiOPO4 (KTP), an inorganic nonlinear optical material with a waveguide figure-of-merit that is twice that of other mixed-metal oxides, contains helical chains of TiO(4/2)O(2/2) octahedra in which a long, short Ti-O bond motif results in a net c-directed polarization. The alternating long and short Ti-O bonds that occur along these chains are the major contributors to the large nonlinear optic and electrooptic coefficients. Analogous chains have been constructed using dichromate [Cr2O7]2- anions and [M(py)4]2+ (M = Cu, Zn) cations; these new transition metal oxides crystallize in the same space group as KTP. Crystal data for Cu(py)4Cr2O7: orthorhombic, space group Pna2(1) (No. 33), with a = 15.941(7) A, b = 16.324(3) A, c = 8.857(2) A, and Z = 4; for Zn(py)4Cr2O7, orthorhombic, space group Pna2(1) (No. 33), with a = 16.503(1) A, b = 16.005(1) A, c = 8.8130(5) A, and Z = 4; for Cd(py)4Cr2O7, monoclinic, space group C2/c (No. 15), with a = 14.8034(9) A, b = 11.1847(7) A, c = 15.788(1) A, beta = 110.023(1) degrees, and Z = 4.

Journal Article↗
PubMed2001

Synthesis and characterization of non-centrosymmetric TeSeO4.

The synthesis, crystal structure, and characterization of a non-centrosymmetric oxide, TeSeO4, are reported. The material was synthesized by combining TeO2 and SeO2 in a quartz tube and heating at 370 degrees C. TeSeO4 has a three-dimensional structure containing [SeO(3/2)](+) cations linked to [TeO(5/2)](-) anions. Both the Se(4+) and the Te(4+) atoms are in asymmetric environments owing to their nonbonded electron pair. The material is SHG active, with a SHG intensity of 400 times SiO(2). Crystal data: monoclinic, space group Ia (No. 9, cell choice 3), with a = 4.3568(8) A, b = 12.465(3) A, c = 6.7176(15) A, beta = 90.825(4) degrees, and Z = 4.

Journal Article↗
PubMed2000

Hydrothermal synthesis of (C6N2H14)2(UVI2UIVO4F12), a mixed-valent one-dimensional uranium oxyfluoride.

A new hybrid organic-inorganic mixed-valent uranium oxyfluoride, (C6N2H14)2(U3O4F12), UFO-17, has been synthesized under hydrothermal conditions using uranium dioxide as the uranium source, hydrofluoric acid as mineralizer, and 1,4-diazabicyclo[2.2.2]octane as template. The single-crystal X-ray structure was determined. Crystals of UFO-17 belonged to the orthorhombic space group Cmcm (no. 63), with a = 14.2660(15) A, b = 24.5130(10) A, c = 7.201(2) A, and Z = 4. The structure reveals parallel uranium-containing chains of two types: one type is composed of edge-sharing UO2F5 units; the other has a backbone of edge-sharing UF8 units, each sharing an edge with a pendant UO2F5 unit. Bond-valence calculations suggest the UF8 groups contain UIV, while the UO2F5 groups contain UVI. EXAFS data give results consistent with the single-crystal X-ray structure determination, while comparison of the uranium LIII-edge XANES of UFO-17 with that of related UIV and UVI compounds supports the oxidation-state assignment. Variable-temperature magnetic susceptibility measurements on UFO-17 and a range of related hybrid organic-inorganic uranium(IV) and uranium(VI) fluorides and oxyfluorides further support the formulation of UFO-17 as a mixed-valent UIV/UVI compound.

Journal Article↗