Poly[[tetra-aqua-(μ₃-4-hy-droxy-pyridine-2,6-di-carboxyl-ato)di-μ₂-oxalato-dipraseodymium(III)] 4.29-hydrate]

The coordination polymer of crystal formula [Pr^III ₂(C₇H₂NO₅)(C₂O₄)₂(H₂O)₄]·4.29H₂O or [Pr^III ₂(HCAM)(ox)₂(H₂O)₄]·4.29H₂O was synthesized from praseodymium(III) nitrate in water using chelidamic acid (H₃CAM) and oxalic acid (H₂ox). There are two Pr^III atoms in the asymmetric unit. One metal ion has nine-fold coordination from one pyridyl nitro-gen and eight oxygen atoms from one HCAM^2-, two ox^2-, and two coordinating water mol-ecules leading to the formation of a tricapped trigonal {Pr^IIINO₈} prism. The other metal ion is coordinated by ten oxygen atoms from two HCAM^2-, two ox^2-, and two coordinating water mol-ecules, forming a bicapped square {Pr^IIIO₁₀} unit. The HCAM^2- linker has a μ₂-κ²:κ¹ chelating coordination mode via its carboxyl-ates and N-pyridyl donors, linking the {Pr^IIINO₈} and {Pr^IIIO₁₀} units into infinite chains. The μ₂-κ¹:κ¹:κ¹:κ¹ bridging carboxyl-ates of the ox^2- linkers connect adjacent chains into sheets in the ac plane. Adjacent layers further aggregate through inter-molecular hydrogen bonding, most of which involves the water mol-ecules of crystallization, and π-π inter-actions to form a tri-periodic supra-molecular framework. Some of the co-crystallizing water mol-ecules as well as one of the metal-coordinating water mol-ecules are disordered.