ABSTRACT
Bi metal dissolves in excess molten phosphorus selenide at 500 degrees C to yield black, rodlike, air- and water-stable beta-Bi(4)(P(2)Se(6))(3) crystals. The phase crystallizes in the triclinic space group P&onemacr; (No. 2) with the room-temperature cell parameters a = 12.2303(8) Å, b = 6.7640(4) Å, c = 17.866 Å, alpha = 90.493(6) degrees, beta = 94.133(6) degrees, and gamma = 91.163(6) degrees. The new structure is a complicated, three-dimensional framework built from [Bi(4)Se(22)] ribbons connected to each other by sharing selenium atoms. The [P(2)Se(6)](4)(-) ethane-like units are found inside and between the [Bi(4)Se(22)] ribbons. The compound is a semiconductor with a band gap of 1.32 eV. It melts with decomposition at 512 degrees C, converting partially to Bi(2)Se(3) and a P(x)()Se(y)() glassy material. Far-IR and Raman spectra show characteristic stretches for the [P(2)Se(6)](4)(-) ligand and Bi-Se vibrations. The structural and chemical relationships of this compound with the alpha-form are discussed.
ABSTRACT
A quaterthiophene derivative, 5,5' "-bis(aminoethyl)-2,2':5',2' ':5' ',2' "-quaterthiophene (AEQT), has been selected for incorporation within the layered organic-inorganic perovskite structure. In addition to having an appropriate molecular shape and two tethering aminoethyl groups to bond to the inorganic framework, AEQT is also a dye and can influence the optical properties of lead(II) halide-based perovskites. Crystals of C(20)H(22)S(4)N(2)PbBr(4) were grown from a slowly cooled aqueous solution containing lead(II) bromide and quaterthiophene derivative (AEQT.2HBr) salts. The new layered perovskite adopts a monoclinic (C2/c) subcell with the lattice parameters a = 39.741(2) Å, b = 5.8420(3) Å, c = 11.5734(6) Å, beta = 92.360(1) degrees, and Z = 4. Broad superstructure peaks are observed in the X-ray diffraction data, indicative of a poorly ordered, doubled supercell along both the a and b axes. The quaterthiophene segment of AEQT(2+) is nearly planar, with a syn-anti-syn relationship between adjacent thiophene rings. Each quaterthiophene chromophore is ordered between nearest-neighbor lead(II) bromide sheets in a herringbone arrangement with respect to neighboring quaterthiophenes. Room temperature optical absorption spectra for thermally ablated films of the perovskites (AEQT)PbX(4) (X = Cl, Br, I) exhibit an exciton peak arising from the lead(II) halide sheets, along with absorption from the quaterthiophene moiety. No evidence of the inorganic sheet excitonic transition is observed in the photoluminescence spectra for any of the chromophore-containing perovskites. However, strong quaterthiophene photoluminescence is observed for X = Cl, with an emission peak at approximately lambda(max) = 532 nm. Similar photoluminescence is observed for the X = Br and I materials, but with substantial quenching, as the inorganic layer band gap decreases relative to the chromophore HOMO-LUMO gap.
ABSTRACT
The reaction of Ce or Gd with a molten mixture of A(2)Se/P(2)Se(5)/Se (A = Rb, Cs) produced the quaternary compounds Rb(3)CeP(2)Se(8) (I) and Cs(3)GdP(2)Se(8) (II), as well as Rb(2)CeP(2)Se(7) (III) and Rb(2)GdP(2)Se(7) (IV). The orange crystals of I, II and the red crystals of III, IV are air- and water-sensitive. Compounds I, II crystallize in the monoclinic space group P2(1)/c, and for I, a = 9.6013(2) Å, b = 18.0604(1) Å, c = 10.0931(1) Å, beta = 90.619(1) degrees, and Z = 4. Compounds III, IV crystallize in the monoclinic space group P2(1)/n, and for IV, a = 10.137(2) Å, b = 7.212(1) Å, c = 20.299(2) Å, beta = 98.23(1) degrees, and Z = 4. Compounds I, II have a 1-D structure with [(RE)P(2)Se(8)](n)()(3)(n)()(-) chains separated by A(+) cations. The RE(3+) lanthanide cation is in a bicapped trigonal prismatic coordination with four tridentate [PSe(4)](3)(-) ligands. Compounds III, IV possess a 2-D structure. Each layer consists of [RE(PSe(4))](x)() "chains" interstitched in two dimensions by hexadentate [P(2)Se(6)](4)(-) ligands. The trivalent RE cation is in a square antiprismatic coordination. The compounds were characterized with differential thermal analysis, far-IR, and solid-state UV/vis diffuse reflectance spectroscopy. Magnetic measurements indicate that the compounds obey the Curie law with &mgr;(eff) values close to those of the free RE(3+) ions.
ABSTRACT
The reaction of Pd with a molten mixture of A(2)Q(x)()/P(2)Q(5)/Q (A = K, Q = S, x = 3; A = Cs, Q = Se, x = 1) produced the molecular compounds K(4)Pd(PS(4))(2) (I), Cs(4)Pd(PSe(4))(2) (II), and Cs(10)Pd(PSe(4))(4) (III) and the solid-state KPdPS(4) (IV), K(2)PdP(2)S(6) (V), and Cs(2)PdP(2)Se(6) (VI). Compounds I-III are air and water sensitive, while IV-VI are air and water stable. All crystals are red or dark red except those of VI, which are black. All of them exhibit a rodlike shape. Compound I crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 6.380(1) Å, b = 6.897(1) Å, c = 8.999(1) Å, alpha = 87.777(8) degrees, beta = 81.581(8) degrees, gamma = 84.429(9) degrees, and Z = 1. Compound II crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 7.491(2) Å, b = 13.340(2) Å, c = 10.030(3) Å, beta = 92.21(2) degrees, and Z = 2. Compound III crystallizes in the tetragonal space group P&fourmacr;2c (No. 112) with a = b = 13.949(2) Å, c = 11.527(2) Å, and Z = 4. Compound IV crystallizes in the tetragonal space group P4(2)/mnm (No. 136) with a = b = 8.5337(2) Å, c = 10.5595(5) Å, and Z = 4. Compound V crystallizes in the orthorombic space group Pnma (No. 62) with a = 15.612(2) Å, b = 7.0724(7) Å, c = 10.080(1) Å, and Z = 4. Compound VI crystallizes in the monoclinic space group C2/c (No. 15) with a = 12.9750(4) Å, b = 8.3282(2) Å, c = 13.0568(1) Å, beta = 102.940(2) degrees, and Z = 4. Compounds I-III contain the discrete complexes [Pd(PQ(4))(2)](4)(-) (Q = S, Se). The mixed salt III contains additional noncoordinating [PSe(4)](3)(-) units. The structure of IV consists of Pd(II) in square planar sulfur coordination linked by edge-sharing [PS(4)](3)(-) tetrahedral groups to produce one-dimensional chains. The structures of V andVI feature the [P(2)Q(6)](4)(-) (Q = S, Se) group coordinated to the square planar Pd(2+) atoms, yielding [PdP(2)Q(6)](n)()(2)(n)()(-) chains. Physical characterization was performed with DTA, far-IR spectroscopy, solid-state UV/vis diffuse reflectance spectroscopy, and single-crystal optical transmission.
ABSTRACT
The reaction of Pb and Eu with a molten mixture of A(2)Se/P(2)Se(5)/Se produced the quaternary compounds APbPSe(4), A(4)Pb(PSe(4))(2) (A = Rb,Cs), and K(4)Eu(PSe(4))(2). The red crystals of APbPSe(4) are stable in air and water. The orange crystals of A(4)Pb(PSe(4))(2) and K(4)Eu(PSe(4))(2) disintegrate in water and over a long exposure to air. CsPbPSe(4) crystallizes in the orthorhombic space group Pnma (No. 62) with a = 18.607(4) Å, b = 7.096(4) Å, c = 6.612(4) Å, and Z = 4. Rb(4)Pb(PSe(4))(2) crystallizes in the orthorhombic space group Ibam (No. 72) with a = 19.134(9) Å, b = 9.369(3) Å, c = 10.488(3) Å, and Z = 4. The isomorphous K(4)Eu(PSe(4))(2) has a = 19.020(4) Å, b = 9.131(1) Å, c = 10.198(2) Å, and Z = 4. The APbPSe(4) have a layered structure with [PbPSe(4)](n)()(n)()(-) layers separated by A(+) ions. The coordination geometry around Pb is trigonal prismatic. The layers are composed of chains of edge sharing trigonal prisms running along the b-direction. [PSe(4)](3)(-) tetrahedra link these chains along the c-direction by sharing edges and corners with the trigonal prisms. A(4)M(PSe(4))(2) (M = Pb, Eu) has an one-dimensional structure in which [M(PSe(4))(2)](n)()(n)()(-) chains are separated by A(+) ions. The coordination geometry around M is a distorted dodecahedron. Two [PSe(4)](3)(-) ligands bridge two adjacent metal atoms, using three selenium atoms each, forming in this way a chain along the c-direction. The solid state optical absorption spectra of the compounds are reported. All compounds melt congruently in the 597-620 degrees C region.
