Crystal structure and magnetic properties of hydrogen bonded charge-transfer compound – TMPD:TCNB

Abstract

1,2,4,5-Tetracyanobenzene (TCNB), a moderate electron acceptor, reacts readily with N,N,N′,N′-tetramethyl- p-phenylenediamine (TMPD), a strong electron donor, to form black colored TMPD:TCNB complex when treated in 1:1 molar ratio. Single crystal X-ray diffraction studies on this complex showed that molecule of TMPD and TCNB are alternately stacked with an interplanar distance of 3.4 Å between them. The structure of the complex does not seem to show usual π–π interaction between the two aromatic rings, but indicates the presence of n–π interaction localized between the nitrogen atoms of TMPD and the cyano groups of TCNB. Along with this a prominent presence of CN···HAr hydrogen bonded ribbon network between nitrogen of cyanide moiety and hydrogen of neighboring aromatic carbon is observed with distance of 2.610 Å and angle of 147.19°. Magnetic measurements on the powdered compound using SQUID magnetometer (5–20 K) showed that the complex is weakly antiferromagnetic ( θ = −0.85 K). To my best knowledge CN···HAr interaction amongst electron acceptor molecules, to form a ribbon-like network, has not been observed before for a magnetic complex.