Molecular and Crystal Structures of 2-Dicyanomethylene-1,1,3,4,5,5-Hexacyanopentenediide (DHCP) and its Tetrathiafulvalene (TTF) Complex

Abstract

Although the molecular structure of the cyanocarbon anion of (C₁₄N₈)^2- had been expected as 2,3-bis(dicyanomethylene)-1,1,4,4-tetracyanobutandiide, the crystal structure analyses revealed that it has the atomic connectivity corresponding to 2-Dicyanomethylene-1,1,3,4,5,5-hexacyanopentenediide (DHCP). This stable dianion is regarded as being consisted of two dicyanomethylene groups and a planar tetracyanobutandiide. Comparing the dihedral angles between these planar parts among the different kinds of the salts, it is concluded that DHCP shows the structural flexibility. This peculiar nature is regarded as the origin to afford the characteristic molecular packing of (TTF)₂(DHCP)(CH₃CN) in which the segragated stack of TTF and the donor-anion alternating stack co-exist. The salts with BEDT-TTF (ET) and BEDO-TTF (BO) showed the metallic conducting behavior down to liquid helium temperature or below.

Key Words:

• Organic anions
• Crystal structure
• DHCP
• Radical ions