Coordination-driven self-assembly of discrete nanosized molecular cages has become one of the most active areas of supramolecular chemistry. 1 Over the past decade, extensive studies have been made on discrete molecular assemblies M x L y with various values of x and y. 2 Among these metal-ligand clusters, the assembly of M 2 L 4 tetragonal cage remains quite rare, although a few such d-block metal supramolecular complexes have appeared in the literature recently. 3 Canonical symmetric Ln 2 L 4 lanthanide cages have, to the best of our knowledge, never been described. This is clearly due to inherent difficulties in harmonizing the subtle relationship between the versatile coordination modes of the lanthanide metals (coordination numbers usually g8) and the ligand conformations in the synthetic cage systems. Lanthanide discrete cage-like assemblies, however, are of considerable interest in broad scientific areas, especially as the luminescent materials.We have recently reported a series of coordination polymers and supramolecular complexes based on bent five-membered heteroatom-ring-bridged ligands. 4 By taking into account the bent geometry of such spacers, we wondered if the five-membered heteroatom ring-bridged 3,3′-biphenylcarboxylate type ligands could be used as an "organic clip" 5 to bind lanthanide ions into discrete molecular cages, especially the Ln 2 L 4 tetragonal cages.Depending on this ligand-directed approach, 3 a series of lanthanide nanosized tetragonal cages Ln 2 L1 4 (Ln(III) ) La (1), Ce (2), Sm (3), Eu (4), and Tb (5) 6 The X-ray crystal structure analysis (Supporting Information) revealed that 1-5 are isostructural. They crystallize in the high-symmetry tetragonal space group, I4/m. For example 3, each Sm(2) node lies in a distorted singlecapped square antiprism coordination sphere (Figure 1), which is defined by eight carboxylic oxygen and one aquo oxygen donors and with Sm-O distances range from 2.457 to 2.576 Å. 7 For 1-5, the ligand donor to Ln(III) bond lengths simply reflect the ionic radius variation. 7 The most important structural feature of 1-5 is their cationic cage-like structure. As shown in Figure 1, four equivalent L1 ligands act as the desired organic clip to bridge two Ln(2) ions to form a tetragonal prismatic cage. It is interesting that the two phenyl rings on the same L1 ligand are basically coplanar, while the central triazole ring rotates by about 40°with respect to the phenyl plane and orients to the tangential direction of the cage. Such organized manner leaves an opening of ∼6.8 Å in the side of the cage. One (Figure 1). Top view of 3 shows that the four ligands crosswise arrange around the Ln(2)‚‚‚Ln(1)‚‚‚Ln(2) axis and the two Ln 2 L1 2 planes are perpendicular to each other, which results in the tetragonal cage canonical. There is a crystallographically imposed C 4 axis passing through these three Ln(III) ions and σ h mirror across the center of the molecule, leading to S 4 symmetry of the cage. The Ln‚‚‚Ln distance is ca. 11 Å, and the distance between the two ...

Four new oxadiazole-bridging ligands (L1-L4) were designed and synthesized by the reaction of 2,5-bis(2-hydroxyphenyl)-1,3,4-oxadiazole with isonicotinoyl chloride and nicotinoyl chloride, respectively. L1 and L3 are unsymmetric single-armed ligands (4- or 3-pyridinecarboxylate arm), and L2 and L4 are symmetric double-armed ligands (4- or 3-pyridinecarboxylate arms). Nine new complexes, [Ag(L1)]PF6.CH3OH (1), [Ag(L1)]ClO4.CH3OH (2), Cu(L2)(NO3)2.2(CH2Cl2) (3), [Cu(L2)2](ClO4)2.2(CH2CCl2) (4), Cu(L2)Cl2 (5), [Cu4(L3)2(H2O)2](L3)4(ClO4)4 (6), [Ag(L4)(C2H5OH)]ClO4 (7), [Ag(L4)(C2H5OH)]BF4 (8), and [Ag(L4)(CH3OH)]SO3CF3 (9), were isolated from the solution reactions based on these four new ligands, respectively. L1, L2, and L3 act as convergent ligands and bind metal ions into discrete molecular complexes. In contrast, L4 exhibits a divergent spacer to link metal ions into one-dimensional coordination polymers. New coordination compounds were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the luminescent and electrical conductive properties of these new compounds were investigated.

Two new symmetric and unsymmetrical semirigid organic ligands 2,5-bis(4-(1H-1,2,4-triazol-1-ylmethyl)phenyl)-1,3,4-oxadiazole (L1) and 4-(1H-1,2,4-trizol-1-ylmethyl)benzoic acid (L2) have been prepared. L2 was generated from L1 by a hydrothermal reaction via the hydrolysis of the central oxadiazole ring of L1. The solution and hydrothermal reactions of L1 with various inorganic M(II) (M ) Cd, Co, Zn, and Cu) ions have been investigated. Compounds [Cd(L1) 3) were obtained in solution by a combination of L1 with corresponding metal salts, while compounds Zn(L2) 2 (4), Co(L2) 2 (5), and [Co(L2) 2 ]‚H 2 O (6) were synthesized by a hydrothermal technique with in situ generated unsymmetrical L2 ligand. In addition, compounds 4-6 could also be prepared by direct combination of L2 with corresponding metal salts under the same hydrothermal conditions. All six new coordination polymers were fully characterized by infrared spectroscopy, elemental analysis, single-crystal X-ray diffraction, and thermogravimetric analysis. Compounds 1-3 are isostructural and feature a onedimensional chain motif composed of an M 2 L 2 -macroring as the based building block. Compounds 4 and 5 form a novel chiral and acentric non-interpenetrating two-dimensional network consisting of right-and left-handed helical ML chains, respectively. Compound 6 adopts a unique non-interpenetrating three-dimensional framework, in which the inorganic ‚‚‚Co-O-Co-O‚‚‚ chains are connected to each other through unsymmetric L2 ligands. In the solid state, L1-L2 and their complexes 1-6 are luminescent. The Kurtz powder measurements show that both 4 and 5 are nonlinear optical (NLO) active and have potential applications as NLO-active materials.

A double Schiff-base ligand 1,4-bis(2-thiazolyl)-2,3-diaza-1,3-butadiene (L8) has been synthesized, and its coordination chemistry with various silver salts AgX (X ) SbF 6 -, SO 3 CF 3 -, H 2 PO 4 -, and NO 3 -) has been investigated. The resulting molecular structures are delicately dependent on the nature of the counterions and the solvent intermedia. Uncoordinating counterions (X ) SbF 6and SO 3 CF 3 -) generated the hydrogen-bonded frameworks based on discrete molecular complex building blocks, whereas coordinating anions (X ) H 2 PO 4and NO 3 -) formed polymeric complexes driven by the metal-anion interactions. Furthermore, the luminescent and electrical conductive properties of some new complexes were investigated.

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