Multistep reversible redox systems, LXVII 2,5-disubstituted N,N '-dicyanobenzoquinonediimines (DCNQIs): Charge-transfer complexes and radical-anion salts and copper salts with ligand alloys: Syntheses, structures and conductivities

The new members of the series of 2,5-disubstituted DCNQIs, Id (Cl/OMe), le (Br/OMe), if (CVI), Ik (Br/I), 11 (I/I), form conducting charge-transfer co mplexes with TTF (tetrathiofulvalene) which are comparable to known DCNQI/T TFs, From these DCNQIs highly conducting radical-anion salts [2-X, 5-Y-DCNQ I](2)M (M=Li, Na, K, NH,, Tl, Rb, Ag, Cu) can also be prepared either from the DCNQIs and MI (not AgI), on a metal wire (Ag, Cu), or by electrocrystal lization (M = Tl, Ag,Cu). For better crystals a method using periodical swi tching between reduction and partial oxidation has been developed. With CF3 (large, strongly electron-attracting) as the substituent in DCNQIs Im (OMe /CF3) and In (Me/CF3), conducting TTF complexes remain whereas only In yiel ds an insulating copper salt. DCNQI-Cu salts with high conductivities are o btained with alloys containing two or three different DCNQIs, The temperatu re-dependent conductivities of DCNQI-M salts (other than copper) are simila r to those of metal-like semiconductors. All new DCNQI-Cu salts are metalli c [M] down to low temperatures, except [fd (Cl/OMe](2)Cu which undergoes a sharp phase transition to an insulating state[M --> I]. By variation of the Ligands or their ratios in conducting alloys of DCNQI-Cu salts temperature -dependent conductivities can be tuned from M --> I to M. In addition, allo ying three ligands produced for the first time a radical salt with temperat ure-independent conductivity from 5 to 300 K. Most remarkably, alloys of th e type [(2,5-Me(2)DCNQI),(m)] Cu/[{2,5-(CD3)(2)-DCNQI}(n)](2)Cu,I,Cu which exhibit a sharp M --> I phase transition on further cooling reenter the con ducting state by an I --> M transition, with changes of ca. 10(8) Scm(-1) b oth ways. For the first time in the field of organic metals crystal structu res of DCNQI-copper salts have been determined by X-ray powder diffraction methods and refined by Rietveld analysis. Unit cell data, coordination angl es and distances of the pi planes are in excellent agreement with the singl e-crystal X-ray data. However, bond lengths and angles of the ligands are t o be less accurate. This powder method proves to be most valuable if only m icrocrystalline material is available.