Inclusion complexes for use in room-temperature gas-sensor design

The inclusion complex [{Co(bpy)(H2O)(4)}center dot(fcds)](n) (1), which has been constructed using the guest molecule ferrocene-1,1'-disulfonate (fcds), the bridging ligand 4,4 '-bipyridine (bpy) and d(7) Co2+, contains an infinite zigzag chain formed by the central Co-II ion and the bridging bpy ligand. Guest fcds molecules lie between two adjacent zigzag chains. The highly conjugated structure of complex 1 means that it can be used as a metal-organic semiconductor, and it also shows a high response to liquefied petroleum gas (LPG) and ethanol/petroleum ether (EP) at room temperature. The inclusion complexes [{Co(bpp)(2)(H2O)(2)}center dot(fcds)center dot 4H(2)O](n) [2; bpp = 1,3-bis(4-pyridyl)propane] and [{Zn(bpy)(H2O)4}center dot(fcds)](n) (3), on the other hand, cannot be employed as room -temperature gas sensors because they are insulators. The electrical resistivity of inclusion complex [{Ni(bpy)(H2O)(4)}center dot(fcds)](n) (4) is 621 M Omega whereas that of [{Co(bpy)(H2O)(4)}SO4 center dot(4-abaH)(2)center dot 3H(2)O](n) (5) (4-abaH = 4-aminobenzoic acid) is only 137 M Omega This means that the semi-conducting properties of such inclusion complexes depend on both the conjugated structure and the central metal ions. Furthermore, conjugated inclusion complexes with an odd number of electrons could be useful for the design of highly selective room-temperature gas sensors. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).