Structural diversity and catalytic properties of five Co2(COO)4 cluster-based coordination polymers modified with R-isophthalic acid (R = H, NO2, CH3, OH and tBu)

The self-assembly of 5-substituted isophthalic acid (R-H2BDC, R = H, -NO2, -CH3, -OH and -Bu-t), Co-II ions and 2,4,6-tris.4-pyridyl)-1,3,5-triazine (TPT) under solvothermal conditions yielded five Co-based coordination polymers (CPs): {[Co.BDC).TPT)]center dot 0.5.H2O)}(n) (CP1), {[Co.NO2-BDC).TPT)]center dot H2O}(n) (CP2), {[Co.CH3BDC).TPT)]center dot 0.5H(2)O}(n) (CP3), {[Co.HO-BDC).TPT)] center dot 0.5H(2)O}(n) (CP4), and {[Co.Bu-t-BDC).TPT)(2/3)] center dot (CH3CH2OH).H2O)} n (CP5) (H2BDC = isophthalic acid, NO2-BDC = 5-nitroisophthalic acid, CH3-BDC = 5-methylisophthalic acid, OH-BDC = 5-hydroxyisophthalic acid and Bu-t-BDC = 5-tert-butylisophthalic acid). All compounds comprise Co-2(COO)(4) binuclear units, which are connected via a combination of R-H2BDC and TPT ligands. In CP1, the binuclear Co-2(COO)(4) units are bridged into 1D chains extending along the [1 1 0] and [-1 1 0] directions, which are further interlinked by TPT ligands into a 3D network with CdS net topology. CP2, CP3 and CP4 are iso-structural and all exhibit 3D frameworks with pcu (alpha-Po) topology. In CP5, the Co-2(COO)(4)units are firstly linked into a 3D NbO net via tBu-BDC ligands, which are further accommodated by size-matching trigonal TPT ligands into a novel (3,8)-connected 3D net. Catalytic measurements show that CP2 and CP3 are good catalysts for the Knoevenagel condensation reaction of benzaldehyde with ethyl cyanoacetate, exhibiting conversions of 91.3% and 96.6% in 120 min, respectively, compared with the other present compounds. In addition, CP2 and CP5 exhibit highly efficient catalytic properties for the selective epoxidation of styrene.