Synthesis, Structures, and Magnetic Properties of Metal-Coordination Polymers with Benzenepentacarboxylate Linkers

Three hybrid organic−inorganic coordination polymers with benzenepentacarboxylate (BPCA) linkers, [Co3(C6H(COO)5)(OH)(H2O)3] (1-Co), [Zn3(C6H(COO)5)(OH)(H2O)3] (2-Zn), and [Co5(C6H(COO)5)2(H2O)12]·(H2O)12 (3-Co), were
synthesized hydrothermally and were characterized structurally and magnetically. 1-Co and 2-Zn are isostructural
[C2/c; Z = 8; 1-Co, a = 19.5350(6) Å, b = 10.4494(4) Å, and c = 13.2353(5) Å, β = 97.2768(8)°; 2-Zn, a =
19.5418(9) Å, b = 10.3220(10) Å, and c = 13.4660(10) Å, β = 98.455(10)°] with three-dimensional structures
that contain [M6] secondary building units bridged by BPCA ligands. A different cobalt-based compound, 3-Co,
forms at lower pH and lower reaction temperature. Its structure [P21/c; Z = 2; a = 12.6162(2) Å, b = 11.3768(2)
Å, and c = 15.3401(3) Å, β = 91.539(1)°] is a more loosely packed framework with free (noncoordinated) carboxylic
groups pointing at water-filled cavities in the framework. The magnetic phase diagram of 1-Co established through
detailed magnetic measurements shows a metamagnetic transition below TN = 3.8 K. The less-packed compound
3-Co, on the other hand, remains paramagnetic above 1.9 K. The three compounds are the first examples of
coordination polymers with benzenepentacarboxylate linkers and fill the gap of coordination polymers involving
benzenepolycarboxylate linkers of the general type C6H6-n(COOH)n, where n = 2−6.