Organic-inorganic hybrid materials enable the integration of useful organic and inorganic characteristics within a single molecular-scale composite. Unique electronic and optical properties have been observed, and many others can be envisioned for this promising class of materials. In this paper, we review the crystal structures and physical properties of one family of crystalline, self-assembling, organic-inorganic hybrids based on the layered perovskite framework. In addition to exhibiting a number of potentially useful properties, the hybrids can be deposited as thin films using simple and inexpensive techniques, such as spin coating or singlesource thermal ablation. The relatively new field of "organic-inorganic electronics" offers a variety of exciting technological opportunities. Several recent demonstrations of electronic and optical devices based on organic-inorganic perovskites are presented as examples.

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.

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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.

The synthesis of the one-dimensional K2Hg3Q4 (Q = S, Se) and Cs2Hg3Se4 and the three-dimensional A2Hg6S7 (A = K, Rb, Cs), and A2Hg6Se7 (A = Rb, Cs) in reactive A2Q x fluxes is reported. Pale yellow, hexagonal plates of K2Hg3S4 crystallize in space group Pbcn, with a = 10.561(5) Å, b = 6.534(3) Å, and c = 13.706(2) Å, V = 945.8(7) Å, d calc = 5.68 g/cm3, and final R = 5.7%, R w = 6.3%. Red, hexagonal plates of K2Hg3Se4 crystallize in space group Pbcn, with a = 10.820(2) Å, b = 6.783(1) Å, and c = 14.042(2) Å, V = 1030.6(5) Å, d calc = 6.42 g/cm3, and final R = 7.7%, R w = 8.4%. Orange yellow, hexagonal plates of Cs2Hg3Se4 crystallize in space group Pbcn, with a = 12.047(4) Å, b = 6.465(2) Å, and c = 14.771(6) Å, V = 1150.4(7) Å, d calc = 6.83 g/cm3, and final R = 5.5%, R w = 6.2%. Black needles of K2Hg6S7 crystallize in space group P4̄21 m, with a = 13.805(8) Å and c = 4.080(3) Å, V = 778(1) Å, d calc = 6.43 g/cm3, and final R = 3.1%, R w = 3.6%. Black needles of Rb2Hg6S7 crystallize in space group P42 nm, with a = 13.9221(8) Å and c = 4.1204(2) Å, V = 798.6(1) Å, d calc = 6.65 g/cm3, and final R = 4.3%, R w = 5.0%. Black needles of Cs2Hg6S7 crystallize in space group P42 nm, with a = 13.958(4) Å and c = 4.159(2) Å, V = 810.2(8) Å, d calc = 6.94 g/cm3, and final R = 4.3%, R w = 4.4%. Black needles of Cs2Hg6Se7 crystallize in space group P42 nm, with a = 14.505(7) Å and c = 4.308(2) Å, V = 906(1) Å, d calc = 7.41 g/cm3, and final R = 3.6%, R w = 4.0%. The A2Hg3Q4 compounds contain linear chains. The A2Hg6Q7 compounds display noncentrosymmetric frameworks with A+ cations residing in tunnels formed by both tetrahedral and linear Hg atoms. K2Hg6S7, Rb2Hg6S7, Cs2Hg6S7, Rb2Hg6Se7, and Cs2Hg6Se7 display room-temperature bandgaps of 1.51, 1.55, 1.61, 1.13, and 1.17 eV, respectively. Bandgap engineering through S/Se solid solutions of the type Rb2Hg6Se7 - x S x and Cs2Hg6Se7 - x S x is possible in these materials. All A2Hg6Q7 melt congruently, with melting points of 556 ± 10 °C, except for Rb2Hg6Se7 which degrades. Rb2Hg6S7 can undergo ion exchange reactions with LiI to give Li1.8Rb0.2Hg6S7.

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The reaction of Au with a molten mixture of A 2 Q/P 2 Q 5 /Q (Q ) S, Se) produced the quaternary compounds A 3 AuP 2 Se 8 (A ) K, Rb, Cs) (I-III), A 2 Au 2 P 2 Se 6 (A ) K, Rb) (IV, V), A 2 AuPS 4 (A ) K, Rb, Cs) (VI-VIII), and AAuP 2 S 7 (A ) K, Rb) (IX, X). I-III crystallize in the acentric space group Cc (No. 9): I, a ) 7.122( 2) Å, b ) 12.527(3) Å, c ) 18.666(4) Å, β ) 96.06(2)°, Z ) 4. IV and V crystallize in the space group C2/m (No. 12): IV, a ) 12.289(2) Å, b ) 7.210(1) Å, c ) 8.107(1) Å, β ) 115.13(1)°, Z ) 2. VI and VII crystallize in the space group P2 1 /m (No. 11): VI, a ) 6.518(2) Å, b ) 6.747(2) Å, c ) 9.468(3) Å, β ) 92.98(2)°, Z ) 2. VIII crystallizes in the space group Pbcm (No. 57) with a ) 6.904(3) Å, b ) 20.093(6) Å, c ) 7.025(5) Å, and Z ) 4. IX and X crystallize in the space group C2/c (No. 15): IX, a ) 7.917(3) Å, b ) 9.247(2) Å, c ) 14.968(3) Å, β ) 91.84(9)°, Z ) 4. Compounds I-III have a one-dimensional structure with [AuP 2 Se 8 ] n 3nchains separated by A + cations. The monovalent Au cation is linearly coordinated to the new ligand [P 2 Se 8 ] 4-.IV and V possess a one-dimensional structure with [Au 2 P 2 Se 6 ] n 2nchains separated by A + ions. The monovalent Au cation is linearly coordinated to ethane like [P 2 Se 6 ] 4ligands. VI and VII have a one-dimensional structure with [AuPS 4 ] n 2nchains separated by A + cations. The Au + cation is linearly coordinated to alternating [PS 4 ] 3tetrahedra. The structure of VIII is related to that of I-III with [AuPS 4 ] n 2nchains. The diselenide of the [P 2 Se 8 ] 4unit is replaced by a second, essentially linear, S-Au-S linkage leaving the structure of the chain unchanged. IX and X have the [AuP 2 S 7 ] nchains with square planar Au 3+ centers. The compounds were characterized with differential thermal analysis, far-IR, Raman spectroscopy, solid-state UV/vis diffuse reflectance spectroscopy, and single-crystal optical spectroscopy. Cs 2 AuPS 4 , at T > 375 °C, converts to β-Cs 2 AuPS 4 , which is isostructural to K 2 AuPS 4 .