Co5/Co8-cluster-based coordination polymers showing high-connected self-penetrating networks: syntheses, crystal structures, and magnetic properties.

Two novel Co(II)-cluster-based coordination polymers--namely, [Co5(μ3-OH)2(1,4-ndc)4(bix)2]n (1) and {[Co8(μ3-OH)4(1,4-ndc)6(btp)(H2O)6]·H2O}n (2)--were prepared by hydrothermal reactions of Co(II) perchlorate with 1,4-naphthalenedicarboxylic acid (1,4-H2ndc) and different N-donor coligands (bix = 1,4-bis(imidazol-1-ylmethyl)benzene and btp = 4,4'-bis(triazol-1-ylmethyl)biphenyl). In 1, 10-connected [Co5(μ3-OH)2(COO)8] clusters are extended by the μ4-1,4-ndc(2-) and trans-bix ligands to construct a rare, self-penetrating ile framework that can interestingly be regarded as the cross-link of two interpenetrating 6-connected pcu networks. While for 2, [Co8(μ3-OH)4(COO)12] clusters serve as the 8-connected nodes, which are bridged by the μ4/μ5-1,4-ndc(2-) and trans-btp ligands to afford the highest-connected uninodal self-penetrating (4(20).6(8)) network based on octacobalt clusters. A synthetic and structural comparison of 1 and 2 demonstrates that the features of auxiliary N-donor ligands play a key role in governing the in situ formed clusters and the final 3-D coordination frameworks. Magnetic susceptibility measurements indicate that complex 1 shows an antiferromagnetic interaction between the adjacent Co(II) ions, whereas 2 displays the dominant antiferromagnetic exchanges in 300-50 K and a ferrimagnetic-like behavior at lower temperatures.