Series of Novel 3D Heterometallic Frameworks Based on the Co(II) Coordination Chains and Ln(III) Coordination Layers

A family of novel Co­(II)–Ln­(III) heterometallic coordination polymers [Ln₂Co­(tia)₄(H₂O)₄]_∞ (tia^2– = 5-(1H-1,2,3-triazol-1-yl) isophthalate, Ln = La 1, Ce 2, Pr 3, Nd 4, Sm 5, Eu 6, Gd 7, Tb 8, Dy 9) have been synthesized through in situ ligand transformation reactions, in which 5-(4-carboxy-1H-1,2,3-triazol-1-yl) isophthalic acid (H₃ctia) undergoes decarboxylation and double deprotonation to tia^2–. X-ray structural analysis reveals that compounds 1–9 are isomorphous. The heterometallic Ln³⁺ and Co²⁺ ions are connected by the dianionic linker (tia^2–) to form unique 3D heterometallic frameworks. Moreover, we have systematically investigated the magnetic behaviors and fluorescent properties of these compounds. The out-of-phase ac signals observed for 9 suggest slow magnetization relaxation, which is unusual in 3D coordination polymers, especially in 3D heterometallic frameworks. In NIR regions, complexes 3, 4, 5, and 9 show the characteristic luminescence of the corresponding Ln­(III ions.