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Hybrid Magnetic and Semiconducting Materials Based on Metal Complexes and Organocyanide Electron Acceptors

By Xuan Zhang

Abstract

Multifunctional molecular materials are of high interest because of the coexistence of two or more functionalities such as magnetism, electrical conductivity, and ferroelectric and optical properties. The radical anion of tetracyanoquinodimethane (TCNQ) can serve as a spin-carrying bridge to enhance magnetic exchange interactions between paramagnetic metal ions and electrical conducting columnar stacks that allow for conduction electrons to travel over long distances. In this vein, coordination compounds with metal ions and TCNQ are excellent candidates for combining magnetic properties with electrical conductivity. The goal of my research is to synthesize new bifunctional materials based on organocyanides and to study their structure-property relationships, which will serve as guidelines for the synthesis of molecular materials with enhanced properties that are promising for applications in electronic devices. A facile modular synthetic approach has been developed to introduce partially charged TCNQ species in hybrid inorganic-organic bifunctional magnetic and electrical conducting materials. By taking advantage of the structural breathing features of the metal-organic cations in conjunction with the π-stacking interactions of partially charged TCNQ radicals, an anomalous conducting behavior has been observed in [Co(terpy)2](TCNQ)3•CH3CN, which is composed of alternating semiconducting and spin-crossover layers. A series of isostructural compounds [Ln(TPMA)(μ-TCNQ)(μ-OH)](TCNQ)2·CH3CN (Ln = Dy, Gd, Y) with partially charged TCNQ have also been synthesized and it has been found that the Dy(III) compound exhibited slow relaxation of the magnetization and semiconductivity. This procedure was further generalized to systems containing single-molecule magnets and other functional cationic species with partially charged TCNQ radicals, indicating that this method is highly promising for the synthesis of a variety of bifunctional materials with electrical conducting properties. Magnetic metal-organic frameworks are promising for applications in high density data storage and small molecule recognition and sensors. TCNQ dianion can be employed as a substitute for carboxylate anions in the formation of MOFs that exhibit interesting interactions between the host framework and guest molecules. It has been found that aromatic guest molecules can induce distinct magnetic ordering in the family of magnetic MOFs Fe(TCNQ)(4,4’-bpy)⊃guest. The flexibility of dicyanamidobenzene dianions allows them to be bridging ligands for the formation of interesting structures, including a quadruple helical aperiodic structure

Topics: Organocyanide, TCNQ, Spin-Crossover, Single-molecule magnet, metal-organic frameworks, electrical conductivity
Year: 2016
OAI identifier: oai:oaktrust.library.tamu.edu:1969.1/158066
Provided by: Texas A&M University

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