CRYSTAL-STRUCTURES AND PHYSICAL-PROPERTIES OF 1,6-DIAMINOPYRENE-P-CHLORANIL (DAP-CHL) CHARGE-TRANSFER COMPLEX - 2 POLYMORPHS AND THEIR UNUSUAL ELECTRICAL-PROPERTIES

A combination of 1,6-diaminopyrene and p-chloranil gives two kinds of 1 : 1 charge-transfer complex crystals from a benzene solution. The al pha-form is triclinic, space group <P(1)over bar>, a=8.963(1), b=9.112 (2), c=6.730(1)Angstrom, alpha=99.59(1), beta=99.65(1), gamma=114.43(1 )degrees, V=476.0(1)Angstrom(3), and Z=1; the beta-form is also tricli nic, space group <P(1)over cap>, a=8.123(3),b=9.708(3),c=6.791(2)Angst rom, alpha=110.73(2), beta=108.891(2), gamma=79.11(3)degrees, V=472.3( 3)Angstrom(3), and Z=1. In both crystals, the donors and accepters are neutral, and stack alternately. The main difference between the alpha - and beta-forms is in the overlapping mode. Both crystals are electri cally insulating at the initial states. The alpha-form single crystal, however, undergoes and irreversible conductivity change upon mild hea ting (< 380 K) or fracture of the crystal into powder. In both cases, the conductivity change amounts to 10(6) to 10(8) and the resultant so lids are highly conducting semiconductors. Structural, optical, magnet ic, and solid-state NMR studies suggest that the low-resistance state mainly comprises neutral molecules, despite its high conductivity. The resistivity of beta-DAP-CHL also decreases upon heating to above 400 K, while fracture of the crystal has no effects. The resistivity chang e in beta-DAP-CHL is considered as simple ionization of a part of the components.