Abstract
One-dimensional (1D) halide-bridged Cu(I)–Ni(II) heterometal coordination polymers containing a hexamethylene dithiocarbamate (Hm-dtc) ligand have been synthesized and crystallographically characterized. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the coordination polymers were estimated using UV-Vis-NIR and photoelectron spectroscopies, and it was revealed that these coordination polymers have appropriate HOMO levels for use as dye sensitizers. Direct-current electrical conductivity measurements and impedance measurements indicated that these 1D Cu(I)–Ni(II) heterometal coordination polymers were insulators (σ300K < 10−12 S cm−1). In addition, the coordination polymers were used as sensitizing materials in dye-sensitized solar cells (DSSCs). DSSCs with 1D Cu(I)–Ni(II) heterometal coordination polymers showed lower performances than those with 1D halide-bridged Cu(I)–Cu(II) mixed-valence coordination polymers.
Highlights
The overlaps of the d-orbitals and highest occupied molecular orbitals (HOMOs) and/or lowest unoccupied molecular orbitals (LUMOs) of the ligands in Cu(II)–dithiocarbamate coordination polymers result in the formation of narrow conduction and/or valence bands, inducing strong magnetic interactions and conducting properties
[Hm-dtc = hexamethylene dithiocarbamate; X = Br− (2a), I− (2b)], exhibited semiconducting properties at relatively small activation energies [σ340K = 1.07 × 10−7 S cm−1, Ea = 0.56 eV, (2a); σ340K = 2.46 × 10−7 S cm−1, Ea = 0.48 eV (2b)] [12], and these polymers could be used as sensitizing materials for dye-sensitized solar cells (DSSCs) [27]
We describe the synthesis, X-ray crystal structures, conducting and dielectric properties of new 1D halide-bridged Cu(I)–Ni(II)
Summary
Crystal engineering of coordination polymers is one of the most attractive subjects in the field of materials science because of the polymers’ versatile chemical and physical properties such as magnetic [1,2,3] and conductive [4,5,6,7,8,9,10,11,12,13,14], dielectric [15,16,17], gas-absorbing [18,19,20], and catalytic properties [21,22,23,24]. We demonstrated that one-dimensional (1D) mixed-valence Cu(I)–Cu(II) coordination polymers containing a dithiocarbamate ligand and bromide or iodide anions, [CuI2CuIIX2(Hm-dtc)2(CH3CN)2]n [Hm-dtc = hexamethylene dithiocarbamate; X = Br− (2a), I− (2b)], exhibited semiconducting properties at relatively small activation energies [σ340K = 1.07 × 10−7 S cm−1, Ea = 0.56 eV, (2a); σ340K = 2.46 × 10−7 S cm−1, Ea = 0.48 eV (2b)] [12], and these polymers could be used as sensitizing materials for dye-sensitized solar cells (DSSCs) [27]. We attempted to investigate the DSSCs with new 1D halide-bridged Cu(I)–Ni(II) heterometal coordination polymers containing Hm-dtc; these have crystal structures isomorphous to those of the 1D mixed-valence. Heterometal coordination polymers, [CuI2NiIIX2(Hm-dtc)2(CH3CN)2]n [X = Br− (1a), I− (1b)] and we compare the photovoltaic properties of DSSCs containing 1a, 1b, 2a, 2b and 3 with those of DSSCs containing semiconducting Cu(I)–Cu(II) mixed-valence coordination polymers as sensitizing dyes
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