resumo
The combination of two 8-aminoquinoline-based Schiff base ligands (L1 and L2) with SCN- and Ni(II) has led to the synthesis of two new one-dimensional thiocyanato-bridged coordination polymers: [Ni(L1)(NCS)(2)](n) (1) and [Ni(L2)(NCS)(2)](n) (2). Both compounds are isostructural and consists of regular zigzag thiocyanato-bridged chains with very weak S center dot center dot center dot S interchain interactions. The measured room-temperature conductivities of compounds 1 and 2 (7.0 x 10(-5) and 2.0 x 10(-5) S m(-1), respectively) are indicative of semiconductor behavior which increases in the presence of photoillumination (3.5 x 10(-4) and 4.9 x 10(-4) S m(-1), respectively). The measured I-V characteristics of compound 1 and 2 based thin film metal-semiconductor (MS) junction devices under irradiation and nonirradiation conditions show a nonlinear rectifying behavior, typical of a Schottky diode (SD). The rectification ratios (I-on/I-off) of the SDs in the dark at +/- 2 V (26.96 and 31.96 for 1- and 2-based devices, respectively) increase to 44.19 and 79.42, respectively, upon light irradiation. The photoinduced behavior has been analyzed by thermionic emission theory, and to determine the diode parameters, the Cheung's method has been employed. These diode parameters indicate that compound 2 has a better performance in comparison to compound 1 and that these materials are good candidates for applications in electrochemical devices. Magnetic measurements show that both compounds present ferromagnetic Ni-Ni intrachain and weak antiferromagnetic interchain interactions. The isothermal magnetizations at 2 K show that both compounds are metamagnets with critical fields of ca. 130 mT in 1 and 90 mT in 2 at 2 K. In the ferromagnetic phase (above the critical field), both compounds exhibit a long-range ferromagnetic order with critical temperatures of around 3.5 K in 1 and 3.0 K in 2. DC and AC measurements with different applied DC fields confirm the metamagnetic behaviors and have allowed the determination of the magnetic phase diagram in both compounds.
palavras-chave
BRIDGING THIOCYANATO LIGANDS; METAL-ORGANIC FRAMEWORK; 1D NICKEL(II) COMPLEX; SINGLE-CHAIN MAGNETS; CRYSTAL-STRUCTURE; PHOTOLUMINESCENCE; TEMPERATURE; VERSATILITY; EXPLORATION; TRANSITION
categoria
Chemistry
autores
Ghorai, P; Dey, A; Brandao, P; Benmansour, S; Garcia, CJG; Ray, PP; Saha, A
Grupos
agradecimentos
A.S. gratefully acknowledges the financial support of this work by the DST of India (Sanction No. SB/FT/CS-102/2014, dated-18.07.2015). We also thank the Spanish MINECO (project CTQ2017-87201-P AEI/FEDER, UE) and the Generalidad Valenciana (project Prometeo/2019/076) for financial support.