Two series of novel 3D potentially porous heterometallic Cu–Ln coordination frameworks assembled by 3,4-pyridinedicarboxylic acid with different topologies and channels: syntheses, structures, luminescence and magnetic properties

Abstract

Self-assembly of rare earth salts, Cu(NO₃)₂ and 3,4-pyridinedicarboxylic acid (3,4-pdcH₂) resulted in the formation of two series of 3 d–4f heterometallic coordination polymers: [Ln₂Cu₃(3,4-pdc)₆(H₂O)₁₂]·mH₂O·nCH₃OH (Ln = Eu (1, m = 22, n = 0), Gd (2, m = 22, n = 0) and Tb (3, m = 15.5, n = 5)) and [LnCu(3,4-pdc)₂(OAc)(H₂O)₃]·8H₂O (Ln = Ho (4), Er (5)). Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, PXRD and TGA. The structures of isomorphous complexes 1–3 (Form I) are constructed with irregular (4,4)-connected 2D [Cu₃(3,4-pdc)₆(H₂O)₃]_n sheets pillared by Ln(H₂O)₄, showing an intriguing 3D 3⁶·4¹⁸·5³·6 framework with the treatment of the Ln₂Cu₃ unit as an 8-connected node. Complexes 4 and 5 (Form II) are constructed with (4,4)-connected 2D [Cu(3,4-pdc)₂(H₂O)]_n sheets pillared by bimetallic units Ln₂(OAc)₂(H₂O)₄, exhibiting a fascinating 3D architecture with (4,8)-connected fluorite (4¹²·6¹²·8⁴)(4⁶)₂ topology. There exist different 1D channels in the polymers of Form I and Form II, in which solvent molecules are accommodated. Moreover, their luminescence and magnetic properties have been investigated.