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).

Dysprosium–dianthracene framework showing thermo-responsive magnetic and luminescence properties

“…By assuming that there is only one characteristic relaxation process with one energy barrier and one time constant, the energy barrier can be extracted from eqn (2). 71 ln w 00 w 0 ¼ ln ot 0 ð Þþ U eff kT (2)…”

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure

“…[73][74][75][76] The observed behavior and anisotropic values are similar to other published mononuclear Co(II) complexes in pseudo-octahedral geometry and also in other Co(II) CPs. [77][78][79][80][81][82] Dynamic susceptibility measurements were performed to study the possibility of slow relaxation of the magnetization. Without an applied static dc eld, no c 0 signal was observed; however, when an external dc eld was used, a dependence of c 0 appeared.…”

Metal-directed supramolecular architectures based on the bifunctional ligand 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalic acid

“…It has been verified that there exists a complicated series of factors affecting the structures of CPs, such as the shape of organic ligands, the nature of the metal ions, the reaction temperature, the reaction time, the pH value, the polarity of solvent etc. (Mondal et al, 2018;Wang et al, 2014;Ardila-Suá rez et al, 2019). In addition, various kinds of intermolecular weak interactions, such as hydrogen bonding, stacking, metal-metal interactions etc., are vital in the self-assembly process (Khavasi et al, 2010;Yang et al, 2009;Bala et al, 2013;Mikhalyova et al, 2015;Albold et al, 2019).…”