2,3-Pyrazinedicarboxylates of cobalt(II), nickel(II), and copper(II); magnetic properties and crystal structures

Abstract

Complexes of singly and doubly deprotonated 2,3-pyrazinedicarboxylic acid (pyzdcH2) have been prepared and studied. Crystal data: [Ni(pyzdcH)2(H2O)2], 1, monoclinic, P21/n, a = 9.2897(8) Å, b = 7.6931(8) Å, c = 10.1044(9) Å, β = 93.378(7)°,Z = 2; [Cu(pyzdcH)2]x•2xH2O, 2, monoclinic, P21/n, a = 6.598(1) Å, b = 14.198(2) Å, c = 8.586(2) Å, β = 97.65(2)°, Z = 2;• [Co(pyzdc)(H2O)2]x•2xH2O, 3, monoclinic, C2/c, a = 12.5777(9) Å, b = 7.5191(9) Å, c = 11.839(1) Å, β = 110.754(4)°, Z = 4; [Ni(pyzdc)(H2O)2]x•2xH2O, 4, monoclinic, C2/c, a = 12.4772(7)Å, b = 7.452(1) Å, c = 11.9166(5) Å, β = 112.302(2)°, Z = 4; [Cu(pyzdc)(H2O)2]x•2xH2O, 5, monoclinic, C2/c, a = 12.784(2) Å, b = 7.527(2) Å, c = 12.323(2) Å, β = 116.150(2)°, Z = 4. The structures were solved by Patterson (1), direct (2, 3), or isomorphous replacement methods (4 and 5 are isomorphous with 3) and were refined by full-matrix least-squares procedures to R = 0.028, 0.030, 0.029, 0.030, and 0.030 (Rw = 0.026, 0.029, 0.027, 0.025, and 0.027) for 1894, 1694, 2476, 1867, and 1412 reflections with I ≥ 3σ(F2), respectively. The structure of 1 consists of monometallic [Ni(pyzdcH)2(H2O)2] units linked by hydrogen-bonding interactions in a three-dimensional network. In 2 extended chains of copper ions are linked by double-bridging pyzdcH− groups while 3, 4, and 5 have structures in which pyzdc2− ligands bridge metal centers to form extended linear chains. Magnetic susceptibility studies reveal antiferromagnetic interactions in 1, 2, 3, 4, and 6 (6 is Cu(pyzdc)). The magnitude of exchange (−zJ = 0.033 cm−1 for 1 and −J = 0.11, 0.74, 0.049, and 1.14 cm−1 for 2, 3, 4, and 6, respectively) is discussed in terms of the structures and d-electron configurations involved. Key words: metal 2,3-pyrazinedicarboxylates, synthesis, X-ray structure, antiferromagnetism.