The field of molecular electronics has been under investigation by materials scientists for the last two decades, activity that has increased in recent years as their potential to be components in modern quantum computing devices began to be discussed in a more sophisticated manner. In this field, the challenge is to obtain stable highly conducting materials and to manipulate their properties with external stimuli. As one of the most stable organic radicals, the singly reduced form of TCNQ (7,7,8,8-tetracyanoquinodimethane) has played a central role in the design of many unprecedented conducting materials including the first purely organic conductor (TTF)(TCNQ) (TTF = tetrathiafulvalene) which is nearly metallic and the electrically bistable switching material Cu(TCNQ). The research in this dissertation focused on the application of TCNQ and its derivatives in order to tune the structure and conductivity of these materials, with the overarching goal being to understand the mechanism of conductivity. This dissertation reports the details of the first main-group TCNQ binary compound, Tl(TCNQ). Two distinct polymorphs have been discovered and a remarkable water-induced phase transition from one to the other was observed. With different modes of TCNQ stacking (alternating or homogenous distances), the two polymorphs exhibit very different conductivities, namely 2.4×10^-4 S/cm and 5.4×10^-1 S/cm. With this inspiration, a series of semiconductors, Tl(TCNQX2) (X =Cl, Br, I) was prepared and structurally characterized. The steric effect of the halogen substituents leads to a variety of structures and a band structure simulation has suggested a clear structure-property relationship that involves perturbation of the Tl 6s orbital into the conduction band. Inspired by the switching material Ag(TCNQ), semiconducting frameworks Ag(TCNQCl2) and Ag(TCNQBr2) were prepared by electrocrystallization methods. Importantly, the former material exhibits a high room temperature conductivity of 0.25 S/cm and an unusual room temperature negative differential resistance (NDR) which is the source of intrinsic switching behaviors. The effect of solvent on the structure of these binary phases was also investigated. The series M(TCNQX2)(MeCN)n (M = Cu, Ag; X = Br, I; n =1, 2) was discovered and the interconversion of these solvated phases was studied. The effect of coordinated solvent molecules decreases the density of conducting stacks, consequently leading to a decrease of conductivity.

Research in the fields of molecular conductors and magnets over the past four decades has involved collaborative efforts of chemists and physicists whose common goal is to design useful materials composed of molecular building blocks. Of particular interest are materials whose properties can be tuned by electronic or steric changes in the molecular sub-units. The research on TCNQ derivatives described in this thesis was inspired by the observation that, although a vast amount of research has been directed at understanding binary M(TCNQ•-) materials, analogous compounds based on substituted TCNQ acceptors are surprisingly scarce. Single crystals of a new structure type for the M+(TCNQ)•- binary family were isolated from reactions of two dihalogenated TCNQ derivatives with Cu(I) ions, namely Cu(TCNQX2) (X = Cl, Br). The new 3-D compound Cu(TCNQCl2) exhibits the highest conductivity of the M+(TCNQ)•- series to date, despite the greater separation of TCNQCl2 units as compared to other derivatives. Compounds of lower dimensionality were also obtained, namely the 2-D Cu(TCNQBr2)(CH3CN) and 1-D Cu(TCNQI2)(CH3CN)2 phases. Several 2p-3d heterospin molecular magnets were also synthesized. For example a “magnetic sponge” material based on a 2-D hexagonal framework of composition {[Mn2(TCNQF4)(CH3OH)7.5(H2O)0.5]-(TCNQF4)2•7.5CH3OH}∞, as well as molecular magnets based on first row metal ions and TCNQF4 ligands of composition MII(TCNQF4)-•(TCNQF42-)0.5(CH3CN) (M = Mn, Co) were prepared. In addition, unprecedented isostructural 2-D frameworks based on combinations of first row metal ions with TCNQBr2 radicals of composition [M(TCNQBr2)2(H2O)2]∞ (M = Mn, Zn) were synthesized. Lanthanide chemistry is also described in this dissertation. A series of mononuclear Ln-TCNQF4 heterospin complexes of composition {MIII[TCNQF4]2[H2O]x}(TCNQF4)(3H2O) (M = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er and Yb) was also obtained which exhibit remarkable properties. In this family of compounds there exists an unprecedented subtle interplay between single molecule magnetic behavior and phonon bottleneck effect behavior for the Tb analogue. Magnetic ordering was observed for the Sm analogue. A homologous series of 1-D materials based on alternating lanthanide ions and hexacyanometallates of formula {[Ln(tptz)(H2O)4Fe(CN)6]•8H2O}∞ (Ln = Pr, Nd, Sm, Eu, Gd, Tb) was obtained and a detailed magnetic study provided incontrovertible evidence that the SmIII-[FeIII(CN)6]3- compound exhibits ferromagnetic and not antiferromagnetic coupling as had been reported for related 1-D chains.