A crystal engineering study of molecular electronic behaviour in TCNQ salts

This thesis explores the “crystal engineering” of the solid-state behaviour of a series of alkali metal TCNQ salts. This can exhibit a variety of electronic and magnetic properties, depending on the solid-state architecture. TCNQ is a good one-electron acceptor and the resulting radical anion salt is quite stable. The architectural behaviour of TCNQ salts is very dependent on the nature of the counter-cation and the stoichiometry of the material. In the present study, the effect of ionophore-encapsulation of the cation (M = Li, Na, K, Rb and Cs) has been explored using single crystal X-ray diffraction, IR, Raman, EPR and pressed discs conductivity measurements. In addition, the effect of changing the ionophore:metal cation ratio and the presence of additional TCNQ0 has been investigated. 25 new crystal structures have been obtained and analysed in detail and this has grown new insight into the impact of the effect of controlling ion pair interactions through ionophore complexation and of steric factors on the nature of TCNQ assemblies adopted. A range of solid-state motifs have been observed including some novel solid-state behaviour. In addition, the solid-state behaviour of two hydrated lanthanide TCNQ salts has been investigated

Architectural diversity in the solid-state behaviour of crown ether and [2.2.2]-cryptand complexes of K+TCNQ˙− salts

The solid-state behaviour of five ionophore-encapsulated TCNQ complexes: (18-crown-6)K(TCNQ)2.5 (1), ([2.2.2]-cryptand)K(TCNQ)2.5 (2), (benzo-18-crown-6)K(TCNQ)2 (3), (dibenzo-18-crown-6)K(TCNQ)2 (4), and (dicyclohexano-18-crown-6)K(TCNQ)3 (5) has been explored. For both 1 and 2, the TCNQ components assemble as a pentameric repeat unit within infinite TCNQ columns with the cation complex sitting in a cavity between the columns; whereas for 3 and 4, neighbouring (crown ether)K+ complexes form dimers involving K+–π interactions which further assemble into one-dimensional columns sitting between infinite TCNQ stacks. In the solid-state complex 5, the crown ether adopts a chair conformation with the resulting (crown ether)K+ complex assembling into a one-dimensional ladder. Pairs of TCNQ dimers separated by an isolated TCNQ unit form infinite TCNQ columns. IR and Raman spectroscopy reveal the presence of partially charged TCNQ units within all five TCNQ complexes (1–5) and resistivity studies indicate that all five TCNQ complexes (1–5) are more conductive than the corresponding simple KTCNQ salts. Preliminary EPR studies of 1 and 2 indicate typical behaviour of complex TCNQ salts (containing both TCNQ0 and TCNQ˙−)

Crown ether alkali metal TCNQ complexes revisited – the impact of smaller cation complexes on their solid-state architecture and properties

The solid-state behaviour of four alkali metal TCNQ complexes: (15-crown-5)LiTCNQ (1), (15-crown-5)NaTCNQ (2), (15-crown-5)Li(TCNQ)2.H2O (3.H2O) and (15-crown-5)Na(TCNQ)2.H2O (4.H2O) has been explored by single crystal X-ray diffraction, Infrared (IR), Raman and Electron Paramagnetic Resonance (EPR) measurements. The presence of a small cation and ionophore leads to subtle changes in behaviour compared with their larger alkali metal analogues and in the hydrated salts water bridges form links between the crown-encapsulated cations and neighbouring TCNQ stacks

Novel TCNQ-stacking motifs in (12-Crown-4)-complexes of Alkali Metal TCNQ Salts

An investigation of the solid-state behaviour of five 12-crown-4 alkali metal TCNQ complexes, (12-crown-4)2LiTCNQ (1), (12-crown-4)2NaTCNQ (2), (12-crown-4)2Li(TCNQ)2 (3), (12-crown-4)2Na(TCNQ)2 (4), and (12-crown-4)2K(TCNQ)2 (5), reveals an unusual “cross-stich” packing motif with the extended face-to-face π-stacked TCNQ•‒ columns present in complexes 1 and 2. The effect of the presence of additional neutral TCNQ0 has also been explored