Paramagnetic Molecular Semiconductors Combining Anisotropic Magnetic Ions with TCNQ Radical Anions

We report the synthesis, magnetic properties, and transport properties of paramagnetic metal complexes, [Co(DMF)₄(TCNQ)₂](TCNQ)₂ (1), [La(DMF)₈(TCNQ)](TCNQ)₅ (2), and [Nd(DMF)₇(TCNQ)](TCNQ)₅ (3) (DMF = N,N-dimethylformamide, TCNQ = 7,7,8,8-tetracyanoquinodimethane). All three compounds contain fractionally charged TCNQ^δ- anions (0 < δ < 1) and mononuclear complex cations in which the coordination environment of a metal center includes several DMF molecules and one or two terminally coordinated TCNQ^δ- anions. The coordinated TCNQ^δ- anions participate in π-π stacking interactions with noncoordinated TCNQ^δ- anions, forming columnar substructures that provide efficient charge-transporting pathways. As a result, temperature-dependent conductivity measurements demonstrate that all three compounds exhibit semiconducting behavior.

Simultaneous Spin-Crossover Transition and Conductivity Switching in a Dinuclear Iron(II) Coordination Compound Based on 7,7',8,8'-Tetracyano-p-quinodimethane

The reaction of Fe(OAc)₂ and Hbpypz with neutral TCNQ results in the formation of [Fe₂ (bpypz)₂ (TCNQ)₂ ](TCNQ)₂ (1), in which Hbpypz=3,5-bis(2-pyridyl)pyrazole and TCNQ=7,7',8,8'-tetracyano-p-quinodimethane. Crystal packing of 1 with uncoordinated TCNQ and π-π stacking of bpypz^- ligands produces an extended two-dimensional supramolecular coordination assembly. Temperature dependence of the dc magnetic susceptibility and heat capacity measurements indicate that 1 undergoes an abrupt spin crossover (SCO) with thermal spin transition temperatures of 339 and 337 K for the heating and cooling modes, respectively, resulting in a thermal hysteresis of 2 K. Remarkably, the temperature dependence of dc electrical transport exhibits a transition that coincides with thermal SCO, demonstrating the thermally induced magnetic and electrical bistability of 1, strongly correlating magnetism with electrical conductivity. This outstanding feature leads to thermally induced simultaneous switching of magnetism and electrical conductivity and a magnetoresistance effect.

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

Water molecules play a key structure-organising role in the crystallisation of 15-crown-5 complexes of lithium and sodium TCNQ in the presence of excess TCNQ⁰.

Temperature-dependent 3D structures of lanthanide coordination polymers based on dicarboxylate mixed ligands

Four families of fourteen three-dimensional (3D) lanthanide coordination polymers (CPs) with dicarboxylate mixed ligands have been synthesized hydrothermally at different temperatures.

Three alkaline-earth metal complexes with 3D networks constructed from a 7,7,8,8-tetracyanoquinodimethane ligand: synthesis, structure and electrochemical properties

Three new 7,7,8,8-tetracyanoquinodimethane (TCNQ) alkaline-earth metal complexes, namely {[M2(TCNQ)3(H2O)6]·TCNQ}n (M = Ca (1), Sr (2) and Ba (3)) have been synthesized by salt elimination reactions. X-ray crystallographic analysis reveals that complexes 1, 2 and 3 are isomorphic featuring a unique 3D structure. Cyclic and differential pulse voltammograms for complexes 1-3 show a reversible one-electron oxidation and a reversible one-electron reduction within the electrochemical window of CH3CN. Their electrochemical HOMO-LUMO gap and reversibility are examined.