Field-Induced Slow Magnetic Relaxation and Anion/Solvent Dependent Proton Conduction in Cobalt(II) Coordination Polymers

Abstract

Three new coordination polymers (CPs), namely, 2D {[Co(L)2(H2O)2](ClO4)2·3DMA·0.4H2O}n (1), 3D {[Co(L)2(H2O)2]·(Cl)2}n (2), and 2D {[Co(L)2(NCS)2]}n (3) were obtained by the self-assembly of corresponding cobalt(II) salts and a linear semirigid linker bis(4-imidazol-1-yl-phenyl)diazene (L) designed with two terminal imidazole groups and an azo moiety in the middle. CPs 1 and 2 are composed of a cationic framework which leads to incorporation of anion in the framework along with solvent molecules (only in 1), whereas CP 3 possesses a neutral framework. The cationic core adopts a cis and trans configuration in 1 and 2, respectively. The structures consist of 2D net with sql topology in 1, eightfold interpenetrating 3-periodic network with dia topology in 2 and threefold interpenetrating 2-periodic network with sql (2,4L2) topology in 3. The structural diversity of CPs 1–3 is governed by several factors, including the different coordination ability of the anions, reaction conditions and intermolecular interactions. Using the method of molecular Voronoi polyhedral, all intermolecular interactions in CPs 1–3 have been analyzed. Magnetic susceptibility measurements in the range 2–300 K reveal that in these CPs Co(II) ions behave as magnetically isolated centers with a significant orbital contribution to the magnetic moment. Alternating current (ac) measurements show signature of slow magnetic relaxation in these CPs. Ab initio investigations on simplified model structures indicate that CoII nodes in the CPs exhibit easy-plane magnetic anisotropy. Furthermore, CP 1 displays significant value of proton conductivity which reaches up to 3.96 × 10–4 S cm–1 at 80 °C and 95% relative humidity (RH).