Synthesis and properties of pyrazine-pillared Ag3Mo2O4F7 and AgReO4 layered phases

The new pyrazine-pillared solids, AgReO4(C4H4N2) (I) and Ag3Mo2O4F7(C4H4N2)(3) (C4H4N2 = pyrazine, pyz) (II), were synthesized by hydrothermal methods at 150 degrees C and characterized using single crystal X-ray diffraction (I-P2(1)/c, No. 14, Z = 4, a = 7.2238(6) angstrom, b = 7.4940(7) angstrom, c = 15.451(1) angstrom, beta = 92.296(4)degrees; II-P2/n, No. 13, Z = 2, a = 7.6465(9) angstrom, b = 7.1888(5) angstrom, c = 19.142(2) angstrom, beta = 100.284(8)degrees), thermogravimetric analysis, UV-Vis diffuse reflectance, and photoluminescence measurements. Individual Ag(pyz) chains in I are bonded to three perrhenate ReO4- tetrahedra per layer, while each layer in II contains sets of three edge-shared Ag(pyz) chains (pi-pi stacked) that are edge-shared to four Mo2O4F73- dimers. A relatively small interlayer spacing results from the short length of the pyrazine pillars, and which can be removed at just slightly above their preparation temperature, at > 150-175 degrees C, to produce crystalline AgReO4 for I, and Ag2MoO4 and an unidentified product for II. Both pillared solids exhibit strong orange-yellow photoemission, at 575 nm for I and 560 nm for II, arising from electronic excitations across (charge transfer) band gaps of 2.91 and 2.76 eV in each, respectively. Their structures and properties are analyzed with respect to parent 'organic free' silver perrhenate and molybdate solids which manifest similar photoemissions, as well as to the calculated electronic band structures. (c) 2005 Elsevier Inc. All rights reserved.