ELSEVIER SyntheticMetals 86 (1997) 1827-1828 Synthesis and characterization of [Acridinium][Ni(dmit)2]9 a new metallic conductor. Yvonne S. J. Veldhuizen, Jaap G. Haasnoot and Jan Reedijk Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502,230O RA Leiden, The Netherlands Abstract [Acridinium][Ni(dmit)& has been synthesized by electro-oxidation of [acridinium][Ni(dmit)& The compound has been characterized by X-ray crystallography, conductivity measurements and intermolecular orbital overlap integral calculations. The compound shows a metallic conductivity behavior down to 4 K, which was confirmed by the overlap integrals. Keywords: Organic conductors based on radical anion salts, electrocrystallization, X-ray crystallography 1. INTRODUCTION Since the discovery of the superconducting properties of [Me4N][Ni(dmit& a variety of mixed-valence Ni(dmit), compounds in combination with different kinds of cations have been synthesized. Most of these compounds appeared to be semiconductors, where the properties of the compound were determined by the size and the shape of the cation. So far the closed-shell cations used were mostly of the tetraalkylammonium type, alkali metal cations or small cyclic cations. The synthesis of [guanidinium][Ni(dmit)~z in our group showed that a planar cation in combination with Ni(dmit), gives rise to short SS interactions in three dimensions.’ Although being a semiconductor, the guanidinium compound shows a rather high room-temperature conductivity of 32 Scm-‘. Therefore, we decided to study the combination of other planar cations with Ni(dmit),. The first result of this study is the synthesis of [AcrH]mi(dmit)& (AcrH = acridinium, which is presented below). m Acridinium L 2. SYNTHESIS [AcrH][Ni(dmit);?] was synthesized by cation exchange of [Bu,N][Ni(drr$] with a large excess of AcrHBF4. Electro- oxidation of a saturated solution of [AcrHl[Ni(dmit)J in acetonitrile with a constant current of 0.25 pA resulted in black crystals on the platinum anode. 3. CRYSTAL STRUCTURE The crystal structure of [AcrH][Ni(dmit)& has been determined by X-ray crystallography. The crystal data are listed in Table 1. 0379-6779197/$17.00 8 1997 Ekevier Science S.A All rights r-d PI.. SO3794779(%)04608-5 Table 1: Crystallographic data for [AcrH][Ni(dmit)J3 empirical formuJa space group a,A &A C,A a, deg P, deg Y, deg v, A3 Z D cUkd9 g.cme3 R C3lHlO~i3S30 C2/c (No. 15) 39.124(2) 6.4777(S) 20.6206( 11) 90 110.549(5) 90 4893.4(5) 4 (formula units) 2.0829(2) 0.052 The structure contains one and a half independent Ni(dmit), unit in a face-to-face orientation and a half cation, which is disordered across an inversion centre at the centre of its middle ring. The Ni(dmit)z units form two-dimensional sheets in the bc plane of the unit cell. The sheets consist of stacks, built up of trimers of Ni(dmit), units with a small mutual distance of 3.49 A. The distance between two trimers is extremely small, 3.10 A, but more important, the trimers are rotated approximately 30” towards each other along their stacking axis. The rotation can be seen very clear in Figure 1 where the modes of overlap are presented. The rotated overlap is called the ‘spanning overlap mode’ and has been found before in a-[Et [Ni(dmit)&? Me,Nl[Ni(dmit).& and [N,N-dimethylpiperidinium] Both these compounds behave as metallic conductors down to low temperature. SS interactions shorter than 3.70 A, the sum of the van der Waals radii, are found in all three directions. Within the trimer a short interaction of 3.552(2) 8, is found, whereas the shortest intertrimer interaction is 3.4690(19) A. Many short interactions am also found in the interstacking direction, of which the shortest is 3.375(2) A. However, the shortest interaction of all is found in the intersheet direction of the crystal structure, being 3.361(2) A.