The preparation and characterisation of Langmuir–Blodgettfilms of the metal dithiolate charge-transfer complexN-octadecylpyridinium–Pd(dmit)2

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The behaviour of floating layers ofN-octadecylpyridinium–Pd(dmit)2 , complex 1, on the surface of a pure water subphase has been studied using pressure versus area isotherm measurements. Film properties were dependent on the quantity of material spread and the length of time that the layer was aged on the surface of the subphase before compression (spreading time). Area per complex values suggested that a monolayer was formed only if a small amount of material was applied to the subphase and the spreading time was long (several hours). Multilayer Langmuir–Blodgett (LB) films have been deposited onto hydrophilic glass substrates and examined using surface profiling, scanning electron microscopy with energy dispersive X-ray spectroscopy and optical absorption spectroscopy. Observations using electron microscopy showed that films deposited from fresh floating layers contained aggregates that were tens of microns in size. In contrast to previous studies on multilayer films of N-octadecylpyridinium–Ni(dmit)2 complex, the LB films of complex 1 were electrically conductive without any post deposition doping treatment, with room temperature, in-plane conductivity values as high as 0.15±0.10 S cm–1 . In some cases, super-Ohmic current versus voltage characteristics were recorded, which has been attributed to space-charge-limited conductivity. Multilayers transferred from aged floating layers did not exhibit significant bulk conductivity, either in the as-deposited state or after iodine doping, although some samples contained highly conductive crystallites that were several hundred microns in size. The single crystal X-ray structure of the analogous N-dodecylpyridinium–Pd(dmit)2 complex is reported, which provides the first structural study of a [Pd(dmit)2 ]–monoanion. The anions pack in centrosymmetric dimers, with an interplanar spacing of ca. 3.5 A and Pd‥S(5′) contacts of 3.57 A, which are separated by N-dodecylpyridinium cations (with a Pd‥N contact of 3.83 A).