Paramagnetic Semiconductors:Hybrid Molecular Materials Based on Ethyl-and Methyl-pyridinium-Substituted Verdazyl Radical Cations and the Ni(dmit)_2 Anion(dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)

摘要

Four kinds of 1:1 salts of 3-(4-and 3-alkyl-pyridinium)-1,5-diphenylverdazyl(alkyl = ethyl and methyl)radical cations with the Ni(dmit)_2 anion([p-EtPyDV]~+[Ni(dmit)_2]~-(1),[m-EtPyDV]~+[Ni(dmit)_2]~-(2),[p-MePyDV]~+[Ni(dmit)_2]~-(3),and [m-MePyDV]~+[Ni(dmit)_2]~-(4))have been prepared.The magnetic properties of salts 1-4 were discussed based on the results obtained by magnetic susceptibility and ESR measurements of 1-4 and the crystal structure analysis of 1.The results of the crystal structure analysis of salt 1 indicate the dimer formation in Ni(dmit)_2 anion molecules,and the dimers are sandwiched between two verdazyl cations [p-EtPyDV]~+,indicating the formation of a magnetic linear tetra-mer in 1.The magnetic susceptibility data for salt 1 have been fitted to a four-spin linear tetramer model using an end exchange interaction of 2J_1/k_B =-780 K and a central interaction of 2J_2/k_B = -200 K.The conductivity(sigma)of salts 1,2,3,and 4 at room temperature was sigma = 2.3 x 10~(-5),1.8 x 10~(-4),1.4 x 10~(-5),and 5.4 x 10~9-6)Scm~(-1)with an activation energy of E_A = 0.28,0.52,0.21,and 0.33 eV,respectively.The 1:1 salts 1-4 are new molecular paramagnetic semiconductors.