Yen-Hsiang Liu

Time‐Evolving Self‐Organization and Autonomous Structural Adaptation of Cobalt(II)–Organic Framework Materials with scu and pts Nets

Self-organization is a process, in which an internal system spontaneously opens a new route to increase system complexity without being guided by an external source. The concept of self-organization is central to the understanding of living organisms, biominerals, and new supramolecular materials. For chemistry, self-organizing equilibrium conditions can be controlled by changing a few critical factors (concentration, template, pH, temperature, solvent system, etc.) to generate desirable compounds. However, these explorations seem not to be completely applied in a few particular supramolecular systems. Inspired by biology, to construct a high-order architecture from individual building components, various driving forces may competitively predominate at certain stages of the self-assembly process. A subtle thermodynamic/kinetic balance may control and tune the materials growth delicately. Namely, self-organization processes can be operative if the building components are sufficient and in close proximity, under suitable conditions. If the supply of building units is depleted or reduced, the original equilibrium conditions will change, and a new self-organization process will take place. These intriguing phenomena of self-organization are triggered by an internal stimulus and seem to be easily understood in biology, but the phenomena has not been addressed in the synthesis system of metal–organic framework (MOF) materials. As part of our ongoing efforts in the design and synthesis of functional crystalline materials, we report herein on an intriguing supramolecular system that involves a distinct self-organization process, in which the product structures adapt to autonomous dynamic changes in the ratio of build-

A flexible tris-phosphonate for the design of copper and cobalt coordination polymers: unusual cage array topology and magnetic properties

The reaction of the flexible tris-phosphonate precursor benzene-1,3,5-tris(methylenephosphonic acid) (H6btmp) with CuCl2·2H2O in H2O under hydrothermal conditions afforded the complex [Cu3(btmp)(H2O)3.6]·H2O (1·H2O). A similar reaction between 2,4,6-trimethylbenzene-1,3,5-tris(methylenephosphonic acid) (Me3-H6btmp) and Cu(NO3)2·3H2O or Co(NO3)2·6H2O gave the complex [Cu4(Me3-H2btmp)2(H2O)4] (2) or [Co6(Me3-btmp)2(H2O)4] (3), respectively. The cis,trans,trans-conformation of the flexible tris-phosphonate ligands resulted in the formation of 3D networks 1 and 3. Interestingly, the cis,cis,cis-conformation of the Me3-btmp ligand in 2 results in the formation of M4L2-type copper-based metalloprismatic cages, which can serve as building units for subsequent assemblies with phosphonate (P–O) linkages to afford a 2D array of nanocages. The magnetic study indicated that complexes 1·H2O, 2 and 3 all exhibit antiferromagnetic behaviors. Interestingly, results from alternating current (ac) magnetic susceptibility measurements revealed that complex 3 exhibits slow magnetic relaxation behavior at low temperatures.

A new Cd4-2,4-pyridinedicarboxylate layered coordination polymer consisting of intralayer cavities and reversible network self-adaptation upon dehydration/moisture-absorption

A new robust, highly stable layered coordination polymer, [Cd2(H2O)2(2,4-pyda)2·H2O]n (FJU-3) (2,4-pyda = 2,4-pyridinedicarboxylate) consisting of hydrophilic box-shape intralayer cavities and terminally coordinated water molecules on the layer surfaces was assembled. Two new Cd-pyda coordination modes were observed, leading to the formation of a novel tetra-cadmium pyridinecarboxlate secondary building unit. The dehydration of FJU-3 results in empty hydrophilic cavities that modulate the metal coordination environments on the layer surfaces. The behaviour of dehydration/moisture-absorption of FJU-3 is reversible. Therefore, the regeneration of layer-to-layer hydrogen-bonding interactions results in the reversible transformation of the solid-state stacking of the layered supramolecular network, as evidenced by powder X-ray diffraction and thermogravimetric analyses. In the solid-state, FJU-3 exhibited high thermal stability.

Tuning through-bond Fe(III)/Fe(II) coupling by solvent manipulation of a central ruthenium redox couple.

The relationships between the intervalence energy (E(IT)) and the free energy difference (DeltaG) that exists between the minima of redox isomers (Fe(II)-Ru(III)/Fe(III)-Ru(II)) for various heterobimetallic complexes [(R-Fcpy)Ru(NH(3))(5)](2+/3+) (R = H, ethyl, Br, actyl; Fcpy = (4-pyridyl)ferrocenyl; Ru(NH(3))(5) = pentaam(m)ineruthenium) were examined. The changes in DeltaG for the complexes in various solvents were due to the effects of both solvent donicity and the substituents. The intervalence energy versus DeltaG, DeltaG approximately FDeltaE(1/2) (DeltaE(1/2) = E(1/2)(Fe(III/II)) - E(1/2)(Ru(III/II))), plots for the complexes in various solvents suggest a nuclear reorganization energy (lambda) of approximately 6000 cm(-1) (Chen et al. Inorg. Chem. 2000, 39, 189). For [(R-Fcpy)Ru(NH(3))(5)](2+) and [(et-Fcpy)Ru(NH(3))(4)(py)](2+) (Ru(NH(3))(4) = trans-tetraam(m)ineruthenium; py = pyridine) in various solvents, the E(1/2)(Ru(III/II)) of rutheniumam(m)ine typically was less than the E(1/2)(Fe(III/II)) of the ferrocenyl moiety. However, the low-donicity solvents resulted in relatively large values of E(1/2)(Ru(III/II)) for [(et-Fcpy)Ru(NH(3))(4)(py)](2+/3+/4+). Under our unique solvent conditions, a dramatic end-to-end interaction was observed for the trimetal cation, [(et-Fcpy)(2)Ru(NH(3))(4)](4+), in which the [(et-Fcpy)(2)Ru(NH(3))(4)](4+) included a central trans-tetraam(m)ineruthenium(III) and a terminal Fe(II)/Fe(III) pair. In general, results of electrochemical studies of [(et-Fcpy)(2)Ru(NH(3))(4)](2+) indicated both solvent-tunable E(1/2)(Ru(III/II)) (1 e(-)) and solvent-insensitive E(1/2)(Fe(III/II)) (2 e(-)) redox centers. However, in nitriles, two E(1/2)(Fe(III/II)) peaks were found with DeltaE(1/2)(Fe(III/II) - Fe(III/II)) ranging between 83 and 108 mV at a terminal metal-to-metal distance of up to 15.6 A. Furthermore, the bridging dpi orbital of the ruthenium center mediated efficient end-to-end interaction between the combinations of the terminal Fe(II)-Fe(III)/Fe(III)-Fe(II) pair. To our knowledge, this is the first example of solvent-tunable end-to-end interactions in multimetal complexes.

Dissolution/reorganization toward the destruction/construction of porous cobalt(II)- and nickel(II)-carboxylate coordination polymers.

The alkali-metal-cation-induced structural transformation of porous coordination polymers (CPs), {A(2)[M(3)(btec)(2)(H(2)O)(4)]}(n) (1, A = K, M = Co; 2, A = K, M = Ni; 3, A = Cs, M = Co; and 4, A = Cs, M = Ni; btec = benzene-1,2,4,5-tetracarboxylate), occurred via a unique dissolution/reorganization process in the presence of an alkali chloride (LiCl, NaCl) in water. Treatment of 1 or 2 in an aqueous solution of LiCl resulted in the formation of new metal-carboxylate species [Co(2)(btec)(H(2)O)(10)] x H(2)O (5 x H(2)O) and {Li(2)[Ni(3)(btec)(2)(H(2)O)(10)] x 3.5 H(2)O}(n) (6 x 3.5 H(2)O), respectively. When NaCl was used in place of LiCl under similar reaction conditions, similar dissolution/reorganization processes were observed. The cobalt species 1 and 3 were converted into the metal-carboxylate product [Na(2)Co(btec)(H(2)O)(8)](n) (7), whereas the nickel-carboxylate frameworks 2 and 4 were transformed into {[Na(4)Ni(2)(btec)(2)(H(2)O)(18)] x 3 H(2)O}(n) (8 x 3 H(2)O). Single-crystal X-ray diffraction analysis revealed that 5 x H(2)O is a discrete molecule, which extends to a hydrogen-bonded 3D porous supramolecular network including tetrameric water aggregates. Compound 6 x 3.5 H(2)O adopts a 3D polymeric structure with a novel (2,4,4)-connected net on the basis of a 4-connecting organic node of a btec ligand, a square-planar 4-connecting metallic trans-Ni(O(2)C)(4)(H(2)O)(2) node, and a 2-connecting octahedral metallic trans-Ni(O(2)C)(2)(H(2)O)(4) hinge. Compound 7 possesses a 3D polymeric structure comprised of two types of intercrossed (4,4)-layers, a [Co(II)(btec)]-based layer and a [Na(I)(btec)]-based layer, in a nearly perpendicular orientation (ca. 87 degrees). Compound 8 x 3 H(2)O adopted a 2D sheet network by utilizing heterometallic trinuclear clusters of Na(2)Ni(O(2)C)(5)(H(2)O)(9) as secondary building units. Each sheet is hydrogen-bonded to neighboring units, giving a 3D supramolecular network. It is noteworthy that the dissolution/reorganization process demonstrates the cleavage and reformation of metal-carboxylate bonds, leading to a destruction/construction structural transformation of CPs.

Crystal engineering toward intersecting channels in a interpenetrated diamondoid network based on a net-to-net H-bonding interaction

A thermally stable, four-fold interpenetrating diamondoid coordination network, Cd(imidazole-4-acrylate)2, with open intersecting channels within the interwoven nets, is strategically designed and synthesized on the basis of a spring-like net-to-net hydrogen-bonding interaction.

Pillared-bilayer zinc(II)–organic laminae: pore modification and selective gas adsorption

Three porous metal–organic frameworks, namely {[Zn2(azpy)(aip)2]·2DMF}n (1, azpy = 4,4′-azobipyridine, H2aip = 5-aminoisophthalic acid), {[Zn2(dipytz)(aip)2]·1.15DMF·0.85MeOH}n (2, dipytz = di-3,6-(4-pyridyl)-1,2,4,5-tetrazine) and {[Zn2(tpim)(aip)2]·2.5DMF·2H2O}n (3, tpim = 2,4,5-tri(4-pyridyl)imidazole), were synthesized under mild conditions. All of the compounds consisted of a honeycomb-like layer, [Zn(aip)]n, further pillared by N-donor ligands to form two-dimensional (2D) porous pillared-bilayer frameworks with 1D channels created inside the bilayers (4.1 × 10.1 A2 for 1, 4.1 × 11.1 A2 for 2, and 5.1 × 9.8 A2 for 3). The resulting MOFs showed different pore volumes and channel shapes depending on the length and shape of the pillar ligands (35.7%, 41.7%, and 33.9% for 1–3, respectively). The pore volume in 3 decreased due to the presence of the uncoordinated pyridyl group of the tpim ligand. The frameworks of 1 and 2 show flexible properties upon undergoing solvent-exchange processes and their CO2 adsorption properties are different. These latter properties are affected by the functional groups of the linear pillar ligand (–NN– and tetrazine group). In particular, compound 3 possesses less flexibility upon undergoing a solvent-exchange process and preferentially absorbs CO2 more efficiently rather than H2 and N2.

A series of lanthanide–organic frameworks possessing arrays of 2D intersecting channels within a 3D pillar-supported packed double-decker network and Co2+-induced luminescence modulation

A new family of three-dimensional lanthanide metal–organic frameworks (Ln-MOFs) formulated as {Ln(NDC)1.5(DMF)(H2O)0.5·0.5DMF}n (Ln = Ce, Pr, Nd, Eu; DMF = N,N′-dimethylformamide; NDC = 2,6-naphthalenedicarboxylic acid) (FJU6) was prepared using a combination of extended dicarboxylate ligands and lanthanide cations under mild hydrothermal conditions. FJU6 contains a rare packed double-decker unit. The adjacent packed double-decker units are further pillared by NDC ligands through different coordination modes, resulting in the generation of a porous 3D framework. Notably, arrays of two-dimensional intersecting channels, occupied by coordinated and guest DMF molecules, are found in FJU6. Strong hard acid–hard base interactions between Ln3+ cations and NDC2− anions, along with strong π–π interactions, were observed between packed 2D double-decker architectures, resulting in a high thermal stability of FJU6 as evidenced by TG analysis. The structural diversity and photoluminescence properties of the frameworks were also investigated. Significantly, in the case of Eu-FJU6, the apparent luminescence modulation induced by presence of diverse amounts of cobalt cations is observed.

In situ resolved ligand chirality in preparing a chiral 3D zinc–cyclopentane–tetracarboxylate based coordination polymer

A new chiral, three-dimensional coordination polymer, [Zn2(CPTC)(TBPE)(H2O)]·1.75H2O (FJU-5), (H4CPTC = cyclopentane-1,2,3,4-tetracarboxylic acid, TBPE = trans-1,2-bis(4-pyridyl)-ethylene) belonging to the chiral space group P212121 with an orthorhombic unit cell was prepared under pH controlled hydrothermal conditions. In situ resolved ligand chirality from the original meso-form of the CPTC ligand, which undergoes a configurational conversion during the synthesis of FJU-5, is responsible for the formation of the chiral pillared-layer 3D network. 1D hydrophilic channels consisting of guest water molecules are located within the chiral 3D network. The 3D framework of FJU-5 is highly robust and remains intact even after the removal of both the guest and coordinated water molecules by dehydration, as evidenced by powder X-ray diffraction and thermogravimetric analyses. The dehydration–moisture absorption behaviour of FJU-5 is reversible.

Poly[diaqua­bis(2,2′-bipyridine)tris­(μ4-2,2′-bipyridine-4,4′-dicarboxyl­ato)dineodymium(III)]

In the crystal structure of the title mixed-ligand coordination polymer, [Nd2(C12H6N2O4)3(C10H8N2)2(H2O)2]n, the NdIII ion is in an octahedral coordination environment formed by one water molecule, one chelating 2,2′-bipyridine ligand, and five monodentate carboxylate groups. The local coordination polyhedron around the NdIII ion is a bicapped trigonal prism. Two NdIII centers are bridged by four carboxylate groups to form an Nd2 dimeric unit; these are further connected by 2,2′-bipyridine-4,4′-dicarboxylate linkers, resulting in a layered coordination network.