Temperature-Driven Assembly of Ln(III) (Ln = Nd, Eu, Yb) Coordination Polymers of a Flexible Azo Calix[4]arene Polycarboxylate Ligand

Solvothermal reactions of LnCl3·6H2O (Ln = Nd, Eu, Yb) with equimolar amounts of 5,11,17,23-tetrakis[(m-carboxyphenyl)azo]-25,26,27,28-tetrahydroxycalix[4]arene (H4L) at 90 or 140 °C gave rise to a set of six lanthanide(III) coordination polymers {[Nd2ClL(HCOO)(DMF)3(H2O)]·0.5DMF·MeCN·1.5H2O}n (1), {[Ln2ClL(HCOO)(DMF)]·sol}n (2: Ln = Eu, sol =0.5MeCN·1.5H2O; 3: Ln = Yb, sol = 1.5H2O), and {[H3O][LnL(H2O)]·DMF·MeCN·H2O}n (4: Ln = Nd; 5: Ln = Eu; 6: Ln = Yb). Complexes 1–6 were characterized by elemental analysis, IR, powder X-ray diffraction, and single-crystal X-ray diffraction. Compounds 1–3 have two-dimensional (2D) networks in which [Nd6Cl4L2(DMF)12(H2O)2] units (1) or [Ln6Cl4L2(DMF)2] (Ln = Eu (2), Yb (3)) are interlinked by the carboxyl groups of formates. Compounds 4–6 exhibit 2-fold interpenetrating 2D networks in which each [Ln4L(H2O)4] “four-flier pinwheel” unit works as a planar eight-connecting node to connect its eight equivalents via four L ligands. The formation of 1–6 provided an interesting insight into the temperature effect on the construction of lanthanide(III)/polycarboxylate coordination polymers under solvothermal conditions.