Extended chain 2,3-pyrazinedicarboxylate complexes of manganese(II) and cadmium(II); synthesis and structure and magnetic properties

Abstract

Manganese and cadmium complexes of singly and doubly deprotonated 2,3-pyrazinedicarboxylic acid (pyzdcH₂) have been prepared and studied. Crystal data: [H₃O]_2χ[Mn(pyzdc)₂]_x, 1, monoclinic, C2/c (no. 15), a = 14.472(1) Å, b = 8.475(2) Å, c = 13.0771(9) Å, β = 114.753(4)°,Z = 4; [H₃O]_2x[Cd(pyzdc)₂]_x, 2, monoclinic, C2/c (no. 15),a = 14.4857(9) Å, b = 8.502(1) Å, c = 14.9803(7) Å, β = 126.951(2)°, Z = 4; [Mn(pyzdc)(H₂O)₂]_x•2xH₂O, 3, monoclinic, P2₁/c (no. 14), a = 6.5523(7) Å, b = 7.6702(7) Å, c = 20.5815(6) Å, β = 93.605(5)°, Z = 4; [Cd(pyzdc)(H₂O)₃]_x•xH₂O,4, monoclinic, Cc (no. 9), a = 6.088(1) Å, b = 11.5410(9) Å, c = 15.0624(7) Å, β = 96.532(8)°, Z = 4. The structures were solved by Patterson (1,4) or direct (2,3) methods and were refined by full-matrix least-squares procedures to R = 0.036, 0.025, 0.034, and 0.022 (R_w = 0.032, 0.025, 0.036, and 0.023) for 2825, 4961, 1672, and 2641 reflections with I ≥ 3σ(F²), respectively. The structures of 1 and 2 consist of extended anionic chains of metal ions that are linked by double-bridging pyzdc²⁻groups, with electrical neutrality maintained by the presence of H₃O⁺ cations in the lattice. In 3 double chains of manganese ions are cross-linked by pyzdc²⁻ ligands forming a "ladder-like" motif. The structure of 4 consists of extended chains of cadmium ions in which single pyzdc²⁻ groups bridge metal centres. Magnetic susceptibility studies indicate, at most, only weak antiferromagnetic exchange in 1 but moderately strong antiferromagnetic interactions in 3, mediated by bridging carboxylate groups (J = −0.27 cm⁻¹). Key words: extended chains, manganese, cadmium, 2,3-pyrazinedicarboxylates, X-ray structures, antiferromagnetism.