A LONG C-C BOND IN A TROUBLESOME STRUCTURE. Douglas R. Powell, Department of Chemistry, University of Wisconsin, 1101 University Ave. Madison, WI 53706 USA; Xiang Ouyang, Zhao Hanhua, and Kim R. Dunbar, Department of Chemistry, Michigan State University, East Lansing, MI 48824 USA

The synthesis of Mn(TCNQ)₂ was undertaken as part of a study of the electronic and magnetic properties of compounds with metal-based radicals bonded to organic ligand radicals. In the crystal structure there are two independent Mn sites each on crystallographic 2-fold axes. Both Mn sites are bonded in an octahedral arrangement to two TCNQ^- groups, two CH₃OH groups, and two 1/2[TCNQ]₂^2- groups. The [TCNQ]₂^2- moieties are dimers of TCNQ^- anions joined by a long (1.654(5) Å) (-bond. This type of dimer formation has been seen in other structures.^1-4 The carbons involved in this long bond acquire a tetrahedral geometry blocking a pathway for electron transfer through this group.

This structure was troublesome to solve and refine due to an ambiguity of the Laue symmetry. The cell parameters suggested orthorhombic symmetry [a = 14.4910(6)Å, b = 27.4207(10), c = 13.1146(5), ( = 90.0049(8)^o]. The preliminary merging R values, however, indicated a much better fit for monoclinic symmetry [R_int = 0.127 mmm, 0.125 2/m(a), 0.037 2/m(b), 0.125 2/m(c)]. Solution in the space group C2/c proceeded with only minor difficulties. The refinement showed that the sample was twinned so as to appear pseudo orthorhombic.

1. Acta Cryst. B33, 2428 (1977).

2. Acta Cryst. B34, 540 (1978).

3. J. Am. Chem. Soc. 105, 4608 (1983).

4. Mol. Crystals & Liquid Crystals 150, 473 (1987).