Structural Chemistry and Properties of Metal Oxalates Containing a Long-Spanning Dipyridyl Ligand: Chain, Interpenetrated Diamondoid, Threaded-Loop Layer, and Self-Penetrated Topologies

Hydrothermal reaction of metal oxalate (ox) salts and bis(4-pyridylmethyl)piperazine (bpmp) afforded a series of coordination polymers that were structurally characterized by single-crystal X-ray diffraction. {[Cd(H2O)4(bpmp)](ox)}n (1) and {[Co(H2O)4(bpmp)](ox)}n (2) show isostructural cationic one-dimensional (1D) coordination polymer chain motifs with unligated ox anions. A higher temperature polymorph of 2, {[Co(ox)(bpmp)]·3H2O}n (3), possesses a system of threefold interpenetrated three-dimensional (3D) diamondoid nets. {[Mn(H2O)4(bpmp)] [Mn2(ox)3]·5H2O}n (4) manifests a unique 1D + 2D → 3D polyrotaxane coordination polymer structure with 1D cationic [Mn(H2O)4(bpmp)]n chains threaded through apertures coursing through parallel stacks of anionic [Mn2(ox)3]n two-dimensional (2D) hexagonal layers. {[Cu2(ox)2(bpmp)]·6H2O}n (5) possesses 2D [Cu2(ox)2]n layers pillared by bpmp ligands into a 3D [Cu2(ox)2(bpmp)]n coordination polymer network with an unprecedented 4,4-connected self-penetrated (5383)2(5482) topology. Variable temperature magnetic susceptibility studies showed weak antiferromagnetic coupling along [Co(ox)]n chain submotifs in 3 with concomitant zero-field splitting (J = −4.1(7) cm–1, D = 34.5(6) cm–1), weak antiferromagnetic coupling within the [Mn2(ox)3]n hexagonal layers in 4 (J ∼ −0.5 cm–1), and strong antiferromagnetic coupling within the 2D [Cu2(ox)2]n layers in 5 (J = −220(6) cm–1).