Donor-Type Nickel-Dithiolene Complexes Fused with Bulky Cycloalkane Substituents and Their Application in Molecular Conductors

The effects of substituents on the arrangement of metal-dithiolene complexes based on pi-conjugated systems, which are extensively used to synthesize various functional materials, have not been studied adequately. New donor-type nickel-dithiolene complexes fused with bulky cycloalkane substituents [Ni(C-n-dddt)(2)] (C-5-dddt = 4a,5,6,6a-pentahydro-1,4-benzodithiin-2,3-dithiolate; C-6-dddt = 4a,5,6,7,8,8a-hexahydro-1,4-benzodithiin-2,3-dithiolate; C-7-dddt = 4a,5,6,7,8,9,9a-heptahydro-1,4-benzodithiin-2,3-dithiolate; and C-8-dddt = 4a,5,6,7,8,9,10,10a-octahydro-1,4-benzodithiin-2,3-dithiolate) were synthesized in this study. All the complexes were crystallized in cis-[Ni(cis-C-n-dddt)(2)] conformations with cis-oriented (R,S) conformations around the cycloalkylene groups in the neutral state. Unique molecular arrangements with a three-dimensional network, a one-dimensional column, and a helical molecular arrangement were formed in the crystals owing to the flexible cycloalkane moieties. New 2:1 cation radical crystals of [Ni(C-5-dddt)(2)](2)(X) (X = ClO4- or PF6-), obtained by electrochemical crystallization, exhibited semiconducting behaviors (rho(rt) = 0.8 omega cm, E-a = 0.09 eV for the ClO4- crystal; 4.0 omega cm, 0.13 eV for the PF6- crystal) under ambient pressure due to spin-singlet states between the dimers of the donor, which were in accordance with the conducting behaviors under hydrostatic pressure (rho(rt) = 0.2 omega cm, E-a = 0.07 eV for the ClO4- crystal; 1.0 omega cm, 0.12 eV for the PF6- crystal at 2.0 GPa).

Automated summary

New donor-type nickel-dithiolene complexes with bulky cycloalkane substituents were synthesized, showing unique molecular arrangements in crystals. Cation radical crystals obtained by electrochemical crystallization exhibited semiconducting behaviors, indicating conducting behaviors under hydrostatic pressure as well.