Thiacalix[4]arene-Based Three-Dimensional Coordination Polymers Incorporating Neutral Bridging Coligands

Employing a solvothermal procedure and use of p-tert-butyl-thiacalix[4]arene tetraacetic acid (H(4)TCTA) and the nitrate salts of cobalt(II) and cadmium(II) have enabled isolation of four three-dimensional metal organic frameworks (1-4) in the presence of three different types of neutral bridging coligands. In one case, 3, a mixed metal ion system (Co2+/Na+) was obtained. First, the reaction of H(4)TCTA with Co(NO3)(2)center dot 6H(2)O together with the linear bridging coligand BPY (4,4'-bipyridine) afforded a mixture of two 3D frameworks of types [Co-2(TCTA)(BPY)](n) (1) and [Co-2(TCTA)(BPY)(2)(H2O)(4)](n) (2). Compound 1 features a paddle-wheel unit incorporating Co2+ pairs, Co-2(carboxylate)(4), involving four different TCTA units in two dimensions and BPY pillaring in the third. In 2, 2D sheets consisting of BPY Co repeating chains stacked in an A-B-A-B pattern are pillared by TCTA to yield the 3D motif. In the second reaction system, the use of H(4)TCTA with Co(NO3)(2)center dot 6H(2)O in the presence of the bent bridging coligand BPPA (N,N'-bis(pyridine-4-yl)-isophthalamine) and NaOH afforded {[Co3Na2(TCTA)(2)(BPPA)(2)(H2O)2]center dot 4DMF center dot 4H(2)O}(n) (3). In 3, TCTA yields a honeycomb-shaped 2D sheet via Co 0(carboxylate) bonds; these sheets are linked by Co 0(carboxylate) and Co-(BPPA)-Co bridging bonds to afford the 3D motif. In this case, the Na atom locates inside the calix cavity in a distorted square planar coordination environment and is stabilized by eta(3)-type cation center dot center dot center dot pi interactions. In the third system, the use of H(4)TCTA with Cd(NO3)(2)center dot 6H(2)O in the presence of the flexible bridging coligand diaminohexane (DAH) gave {[Cd-2(TCTA)(DAH)(DMF)2]center dot 2DMF center dot 2H(2)O)(n) (4), which features an unusual PtS-like 3D structure. The results confirm that the nature of the extended 3D structures is influenced by the bridging coordination behavior of the coligands. In all these structures, the TCTA ligands adopt a 1,3-alternate conformation. Thermal gravimetric analysis performed on the present MOFs revealed that three of these compounds have high thermal stability (similar to 300 degrees C).