Structure, Hydrogen Bonding and Other Exciting Effects in Low Dimensional TCNQ Salts. Recent Advances

Organic compounds have long been considered the most natural representatives of the insulating state. It started to change about fifty years ago, after the synthesis of an extraordinary organic molecule: tetracyano-p-quinodimethane (TCNQ). This molecule displays unique chemical and physical properties and give rise to a very rich class of organic conducting materials. The common feature of this conductors is high ordering of TCNQ molecules, very often in linear one-dimensional chains or columns. The physical properties of TCNQ salts are determined by two major points: 1) a restricted electronic dimensionality and 2) electronic correlations and electronphonon interactions. The aim of the paper is to review the influence of the properties and spatial structure of the cations on selected physical properties of adequate TCNQ complex salts. Some uncommon effects such as thin layer's molecular organization and anions orientation, multidimensionality of hydrogen bonded networks of the salts - their types and strengths, melting of organic composites based on TCNQ and photoinduced melting of spin-Peierls phase in CT compounds are discussed. Possible applications of TCNQ salts are also mentioned.