Diverse layered topology and magnetic subunits in cobalt cyclohexyldicarboxylate coordination polymers with 3-pyridylnicotinamide coligands

Abstract

Three new divalent cobalt coordination polymers containing anionic cyclohexyldicarboxylate and neutral 3-pyridylnicotinamide (3-pna) tethering ligands have been prepared and structurally characterized via single-crystal X-ray diffraction. These phases show a diversity of layered topologies and differences in cobalt atom aggregation. [Co(cis-12chedc)(3-pna)(H2O)]n (1, cis-12chedc = 4-cyclohexene-cis-1,2-dicarboxylate) shows a standard (4,4) grid topology with magnetically isolated cobalt atoms. [Co(cis-13cdc)(3-pna)]n (2, cis-13cdc = cis-cyclohexane-1,3-dicarboxylate) shows a 2D 3,5-connected net with a previously unreported (3.52)(3253647) topology featuring “infinite” anti–syn bridged {Co(OCO)}n chain motifs pillared by 3-pna ligands. [Co(cis-14cdc)(3-pna)]n (3, cis-14cdc = cis-cyclohexane-1,4-dicarboxylate) shows a 2D 6-connected triangular net with (3,6) topology built from {Co2(OCO)2} dimeric units linked by cis-14cdc and 3-pna tethers. Magnetic susceptibility studies of compound 2 revealed a decrease in χmT product upon cooling, ascribed to antiferromagnetic coupling along the {Co(OCO)}n chain motifs concomitant with Kramers doublet formation (g = 2.24(3), D = 12.8(8) cm−1, J = –0.46(6) cm−1). For compound 3, Kramers doublet formation was also observed, but with ferromagnetic superexchange within its {Co2(OCO)2} dimeric units (g = 2.27(1), D = 24(1) cm−1, J = 0.35(2) cm−1). Thermal decomposition behavior of the three new phases is also discussed.