Synthesis, crystal structures and physical properties of TTF-based conducting charge transfer salts with anions containing selenocyanate ligands

Three new charge transfer salts of tetrathiafulvalene (TTF)based donors with selenocyanate-metal complex anions have been synthesized. The salts have been characterized as BEDT-TTF4[Cr(NCSe)(6)]. CH2Cl2, II, TTF3[Cr(NCSe)(4)phen](2), III and BEDT-TTF2[Cr(NCSe)(4)phen] (.) CH2Cl2, IV, where phen = 1,10'-phenanthroline and BEDT-TTF = bis(ethylenedithio)tetrathia-fulvalene. At 120K, II crystallizes in the P2(1)/m space group with a = 10.454(1), b = 31.990(1), c = 12.339(1) Angstrom, beta = 113.163(2)degrees, V = 3793.8 Angstrom(3), Z = 4 and at 240 K in the same space. group with a = 10.530(1), b = 32.122(1), c = 12.396(1) Angstrom, beta = 113.186(3)degrees, V = 3854.2 Angstrom(3), Z = 4. At 240K III crystallizes in the C2/c space group, a = 38.9272(5), b = 11.2992(1), c = 15.2540(3) Angstrom, beta = 106.8877(6)degrees, V = 6420.1 Angstrom(3), Z = 8. The structure of IV has been solved in the P (1) over bar space group with a = 8.7629(3), b = 11.7977(4), c = 26.6031(9), alpha approximate to 81.697(2), beta = 87.858(3), gamma = 74.8471(14), V = 2626.8 Angstrom(3), Z = 2. All of the salts have numerous (SSe)-Se-... close atomic contacts between donors and acceptors but there is no magnetic exchange between ions, as previously seen in closely related salts such as TTF[Cr(NCS)4phen] and (donor)[M (NCS)4(isoquinoline)21, where M = Cr, Fe and donor = TTF, BEDT-TTF or TMTTF (tetramethyltetrathiafulvalene). Indeed, II and IV are paramagnetic semiconductors whereas III is a paramagnetic insulator. The absence of long-range magnetic order is discussed in terms of structure-function relations since there are no pi-stacking interactions between donor and acceptor, which are seen in all of the bulk magnets of this type where the donor spin is magnetically coupled to the anion. The synthesis and crystal structure of the starting material, [(C4H9)(4)N]3[Cr(NCSe)61, 1, is also reported; it crystallizes in the P (1) over bar space group with a 12.220(1), b = 12.814(1), c = 13.008(1) Angstrom, alpha = 99.608(6), beta = 114.028(5), gamma = 92.637(6)degrees, V = 1819.5 Angstrom(3), Z = 2. (C) 2002 Elseiier Science (USA).