Rigid Linear Ligand Research Articles

Large Negative Linear Compressibility in InH(BDC)₂ from Framework Hinging.

Materials with negative linear compressibility (NLC) counterintuitively expand along one specific direction coupled to the volume reduction when compressed uniformly. NLC with a large value is desired for compression and materials science. However, NLC is generally smaller than -20 TPa-1. High-pressure X-ray diffraction experiments reveal that the β-quartz-like InH(BDC)2 generates an extreme NLC (-62.4 TPa-1) by framework hinging. InH(BDC)2 is much safer and lower-cost than Au+/Ag+ and CN--containing materials that dominated the fields of large NLC. This work reconfirms that a negative thermal expansion flexible framework could likely exhibit large NLC. Moreover, a large NLC could be anticipated to arise from β-quartz-like or related frameworks composed of rigid linear ligands and flexible framework angles.

Syntheses and structures of two new coordination polymers generated from a 4-aminotriazole-bridged organic ligand and CoII salts

Organic ligands and counter-anions influence the coordination spheres of metal cations and hence the construction of coordination polymers (CPs). The specific bent geometries of five-membered heterocyclic triazole bridging organic ligands are capable of generating CPs with novel patterns not easily obtained using rigid linear ligands. A multidentate 4-aminotriazole-bridged organic ligand, namely 4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole (L) has been prepared and used to synthesize two CoII coordination polymers, namely poly[[[μ2-4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole-κ2N:N']bis(methanol-κO)cobalt(II)] bis(perchlorate)], {[Co(C22H16N8)2(CH3OH)2](ClO4)2}n, (I), and poly[[μ3-4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole-κ3N:N':N'']dichloridocobalt(II)], [CoCl2(C22H16N8)]n, (II), using CoX2 salts [X = ClO4 for (I) and Cl for (II)] under solvothermal conditions. Single-crystal X-ray structure analysis revealed that they both feature two-dimensional networks. Cobalt is located on an inversion centre in (I) and in a general position in (II). In (I), L functions as a bidentate cis-conformation ligand linking CoII ions, while it functions as a tridentate trans-conformation linker binding CoII ions in (II). In addition, O-H...N and N-H...O hydrogen bonds and C-H...π interactions exist in (I), while N-H...Cl and π-π interactions exist in (II), and these weak interactions play an important role in aligning the two-dimensional nets of (I) and (II) in the solid state. As the compounds were synthesized under the same conditions, the significant structural variations between (I) and (II) are believed to be determined by the different sizes and coordination abilities of the counter-anions. IR spectroscopy and diffuse reflectance UV-Vis spectra were also used to investigate the title compounds.

Structure tuning in amino-functionalized coordination polymers based on different V-shaped dicarboxylate ligands

Two flexible V-shaped dicarboxylate coligands (H2IBG=isophthaloylbisglycine, and H2PPDA=4,4′-(perfluoropropane-2,2-diyl)dibenzoic acid) were selected to construct two new amino-functionalized coordination polymers based on Zn salt and a rigid linear ligand L (L=3,6-di(3-imidazolyl)benzene-1,2-diamine. Both {[Zn(PPDA)(L)]·3H2O}n (1) and {[Zn2(IBG)(L)]·2H2O}n (2) were crystallized in mononuclear structure. Complex 1 shows a 3-D super structure based on ABAB packing, while complex 2 shows a 2-D layered structure. Structural diversity was acquired due to the flexibility of dicarboxylate ligands. Crystallographic and spectroscopic properties of both complexes were explored.

A Porous Cu(II)-MOF with Proline Embellished Cavity: Cooperative Catalysis for the Baylis-Hillman Reaction.

l-Proline has been covalently attached in a rigid linear ligand, H4L, having an isophthalate moiety at each terminal to form the chiral ligand, H4LPRO. This linker has been used for the construction of a porous MOF, LCuPRO. The free l-proline moiety in the cavity of the framework in the presence of imidazole as a cocatalyst functions synergistically to catalyze the Baylis-Hillman reaction between α,β-unsaturated carbonyl compounds and aromatic aldehydes. High porosity of the framework is proven by the nitrogen adsorption isotherm.

Dicarboxylate-dependent structural diversity in amino-functionalized complexes: From mononuclear to multinuclear coordination polymer

Three amino-functionalized coordination polymers with different flexible V-shaped dicarboxylate ligands have been synthesized based on Cd salt and a rigid linear ligand L (L=3,6-di(3-imidazolyl)benzene-1,2-diamine, H2HIP=5-hydroxyisophthalic acid, H2ABA=bis(4-carboxylphenyl)amine, H2IBG=isophthaloylbisglycine): {[Cd(L)1.5(HIP)]·(H2O)}n (1), {[Cd2(L)(ABA)2(H2O)]·(H2O)2}n (2) and {[Cd(L)0.5(IBG)]·(H2O)2}n (3). Complex 1 crystallizes in a mononuclear structure with a 3D hxg-d net. Complex 2 crystallizes in a tetranuclear fashion with a layer structure. Complex 3 shows an infinite rod-shaped secondary building unit (SBU) structure. It implies that the structural diversity in assembly process is determined by the flexibility of dicarboxylate ligands. These complexes were characterized by single crystal X-ray diffraction, infrared spectra, thermogravimetric analysis, elemental analysis, and powder X-ray diffraction measurements. Additionally, luminescent properties of 1–3 have also been explored and all exhibit significant red-shifted emission in the solid state at room temperature compared with free L ligand.

Four new metal–organic frameworks based on a rigid linear ligand: synthesis, optical properties and structural investigation

Four coordination polymers have been synthesized based on a rigid linear carboxylate ligand and different lengths of imidazole ligands.

Crystal Structures and Spectroscopic Properties of Metal–Organic Frameworks Based on Rigid Ligands with Flexible Functional Groups

Two rigid linear ligands with alkoxy functional groups (L1 = 4,4′-(2,5-dimethoxy-1,4-phenylene) dipyridine; L2 = 4,4′-(2,5-diethoxy-1,4-phenylene) dipyridine) incorporating carboxyl-containing auxiliary ligands (isophthalic acid = H2IPA; terephthalic acid = H2TPA; biphenyl-4,4′-dicarboxylate = H2BPDC) have been adopted to build a series of complexes with M(II) (M = Zn, Co, Cd) under solvothermal conditions. The formula of these complexes are {[Zn(L1)(IPA)]}n (1), {[Zn(L1)(TPA)]·DMF}n (2), {[Co(L1)(TPA)(H2O)2]·2DMF}n (3), {[Cd(L1)(TPA)(H2O)2]·2DMF}n (4), and {[Co(L2)(BPDC)]·0.5H2O}n (5). Five complexes have been characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction and thermogravimetry measurements. Topological analyses reveal that complex 2 is a 6-connected pcu net with point symbol {412·63}, while complex 5 is a 6-connected rob net with point symbol {48·68·8}, the other complexes 1, 3, and 4 can be simplified as 4-connected sql nets with point symbol {44.62}. Complexes 1, 3...

Structural Diversity and Luminescence Properties of Coordination Polymers Built With a Rigid Linear Dicarboxylate and Zn(II)/Pb(II) Ion

A rigid linear ligand incorporating a carboxylic acid group at either end, p-terphenyl-4,4″-dicarboxylic acid, 2′,5′-dimethyl (H2L) has been used to construct four coordination polymers with Zn(II) through solvothermal techniques. The four products formed are formulated as {[Zn3(L)2(OH)2]·8EtOH·4DMF}n (1), {[Zn(L)(bpmp)0.5]·EtOH·1/2DMF}n (2), {[(Zn)0.5(L)0.5(py)0.5]·5/2DMF·EtOH}n (3), and [Zn(L)(HNMe2)]n (4). With Pb(NO3)2 the ligand affords two polymers, {[Pb2(L)1.5(O)0.5]·EtOH·2H2O}n (5) and {[Pb3(L)3(H2O)]·6H2O}n (6). All of these compounds have been characterized by single crystal X-ray diffraction, infrared spectroscopy, thermogravimetry, elemental analysis, and powder X-ray diffraction measurements. Topological analyses reveal that complex 2 is a 6-connected pcu net, while complexes 3 and 4 are simplified as a 4-connected sql net. In the case of complexes 1 and 6, one-dimensional rod-shaped metal carboxylate based secondary building units have been obtained. However, an uncommon structure and topology have been obtained in complex 5. Surprisingly, such type of parallel ladder-like packing is not explored much in coordination polymers. Solid-state photoluminescence studies have been carried out for all of the complexes upon excitation at 347 nm at room temperature.

Multicomponent Self-Assembly: Generation of Rigid-Rack Multimetallic Pseudorotaxanes.

The rigid linear ligands 1a-g and the macrocycle 2 undergo self-assembly via coordination with copper(I) ions to generate the series of rigid-rack inorganic pseudorotaxanes 3a-g. These complexes have been characterized by analytical and spectroscopic methods. Their architecture has been confirmed by determination of the crystal structures of 3e,f. The complex [Cu(2)(1e)(2)(2)](PF(6))(2) (3e) crystallizes in the space group C2/c, whereas complex [Cu(2)(1f)(2)(2)](PF(6))(2) (3f) gives crystals containing a single enantiomer in the chiral space group P2(1)2(1)2(1). The synthesis and solution structures of 3a-g and the solid-state structures of 3e,f are discussed in relation to the viability of multicomponent self-assembly as an approach to linear metal-ion arrays.