Qingjin Meng

Crystal Structures and Properties of Large Protonated Water Clusters Encapsulated by Metal−Organic Frameworks

A large ionic water cluster H(H(2)O)(28)(+), consisting of a water shell (H(2)O)(26) and an encaged species H(H(2)O)(2)(+) as a center core, was trapped in the well-modulated cavity of a porous metal-organic framework (MOF) {[Co(4)(dpdo)(12)(PMo(12)O(40))(3)](-)}(infinity) and structurally characterized. Degeneration of the protonated water cluster H(H(2)O)(28)(+) into a smaller cluster H(H(2)O)(21)(+) and recovery of H(H(2)O)(28)(+) from the resulting H(H(2)O)(21)(+) cluster in a reversible way demonstrated the unusual stability of the protonated water clusters H(H(2)O)(28)(+) and H(H(2)O)(21)(+) in the robust crystal host. Proton transport and proton/potassium ion exchange through the channels of the crystal host have been investigated by a well-established fluorometry method. X-ray fluorescence experiments and X-ray structural analyses of the exchanged crystals confirmed the occurrence of the proton/potassium ion-exchange reaction and the transformation of the protonated water cluster H(H(2)O)(28)(+) to an ionic cluster K(H(2)O)(27)(+). Comparison of the H(+)/K(+) exchange of H(H(2)O)(28)(+) with that of its neighboring protonated water cluster H(H(2)O)(27)(+) suggested that the abundance of hydrogen bonds associated with the hydronium/water cluster in the H(H(2)O)(28)(+) cluster was essential for proton transport through the Grotthuss mechanism. On the basis of the results, our porous network could be described as a synthetic non-peptide ion channel, in terms of not only structural features but also the functions addressed. Direct observation of the structures of various large ionic water clusters trapped by porous MOFs, coupled with the proton/ion-exchange processes and the reversible dehydration/rehydration, provided valuable insights into the aqueous proton transfer and its mobility pertaining to the large protonated water clusters in the condensed phase.

Metal–organic frameworks constructed from mixed-ligand 1,2,3,4-tetra-(4-pyridyl)-butane and benzene-polycarboxylate acids: syntheses, structures and physical properties

Three novel coordination polymers, [Mn(TPB)0.5(IPA)(H2O)2]n (1), [Zn1.5(TPB)0.5(TMA)(H2O)·(H2O)]n (2), and [Co(TPB)0.5(PMA)0.5(H2O)2·(H2O)]n (3) (TPB = 1,2,3,4-tetra-(4-pyridyl)-butane; H2IPA = isophthalic acid; H3TMA = trimesic acid; and H4PMA = pyromellitic acid), have been synthesized under hydrothermal conditions and structurally characterized. Complex 1 features a 2D infinite layer framework consisting of bi-manganese clusters, which is further stacked along the [11] direction via strong interlayer π⋯π interactions to form a 3D supramolecular architecture. Complex 2 has a 3D complicated framework comprised of two kinds of infinite 1D chains. The 3D framework of complex 3 possesses three topologically nonequivalent 4-connected nodes synchronously and exhibits an unprecedented (64·102)(42·84)(4·65)2 topology. The magnetic susceptibility data of complex 1 show strong antiferromagnetic interactions in the dinuclear Mn(II) units. Complex 2 exhibits strong fluorescent emissions in the solid state at room temperature and may be suitable as a candidate of blue-fluorescent material.

Four 2D metal–organic networks incorporating Cd-cluster SUBs: hydrothermal synthesis, structures and photoluminescent properties

Hydro(solvo)thermal reactions between 1,1′-biphenyl-2,2′,3,3′-tetracarboxyl acid (H4bptc) and Cd(NO3)2·4H2O at the presence of the ‘second’ ligands of bpydo, bpe, bpp and bix (bpydo = 4,4′-bipyridine-N,N′-dioxide; bpe = 1,2-bis-(4-pyridyl)ethane; bpp = 1,3-Bis-(4-pyridyl)propane; bix = 1,4-bis(imidazol-1-yl-methyl)benzene) yield four new 2D metal–organic coordination polymers [Cd9(bptc)4(μ3-OH)2(H2O)14]·(bpydo)·2H2O (2), [Cd2(bptc)(bpe)(H2O)2]·H2O (3), [Cd4(bptc)(Hbptc)(bpp)(μ3-OH)(H2O)4] (4), [Cd2(bptc)(bix)(H2O)] (5). Compound 2 presents a 2D grid structure with heptanuclear cadmium cluster and two kinds of discrete Cd atoms secondary building units (SUBs), 3 has a 2D structure with the novel Schlafli symbol of (4.62)(43.63)(44.610.8), 4 gives a 2D grid structure with a pentanuclear cadmium cluster, binuclear cadmium cluster and discrete Cd atom SUBs, and 5 has a 2D distorted CdI2-type topology structure with the Schlafli symbol of (43)2(46.66.83). The novel achiral crown-ether-like cycles in 2, 4 and 5 are found and occupied by the single Cd atom or binuclear cadmium cluster. All compounds give strong luminescent emission and have potential application as optical materials.

Complicated magnetic behavior in one-dimensional nickel(III) chain complex [1-(4′-cyanobenzyl)pyridinium][Ni(mnt)2](mnt2−=maleonitriledithiolate)

Abstract A new ion-pair complex [1-(4′-cyanobenzyl)pyridinium] [Ni(mnt)2] (1), in which mnt2−=maleonitriledithiolate, have been fabricated and its X-ray single crystal structural analyses at 293, 180 and 140 K shown that the [Ni(mnt)2]− anions and [CNBzPy]+ cations form a well-separated stacking column along c-axis direction, within which [Ni(mnt)2]− anions are uniformly spaced to give a one-dimensional (1-D) chain structure. Bulk magnetic properties of this complex have been investigated in the temperature range of 2–400 K and shown there exists spin kink at ∼190 K. In low temperature region, weak ferromagnetic behavior occurs in 1.

CoII Molecular Square with Single-Molecule Magnet Properties

A new tetranuclear cobalt(II) molecular square in which adjacent Co(II) centers are linked by a mu(2)-bridging oxygen atom and a N-N bridge along the edges of the square has been designed for single-molecule magnets (SMMs) with high anisotropy barriers. The overall intramolecular ferromagnetic coupling at low temperature combined with the slow relaxation at static zero fields suggests a SMM behavior for this molecular square. The zero-field cooled magnetization (ZFCM) and field cooling magnetization (FCM) at 10 Oe illustrate the nonreversibility and bifurcation below 4.5 K. The deviations of magnetization from the saturated value in strong applied fields demonstrate the participation of low-lying excited states. The peaks of the out-of-phase signals are observed corresponding to coincidence of the applied ac field oscillation frequency with the relaxation rate.

Conformational switching fluorescent chemosensor for chloride anion

A new fluorescent “off–on” signaling chemical sensor with high selectivity for chloride anion through a guest-induced conformational switching process was achieved by using a positively charged tripodal receptor with naphthyl groups attached to the benzoimidazolium arms.

A highly selective fluorescent sensor for fluoride through ESPT signaling transduction

A highly selective fluorescent sensor for fluoride, bis(2-hydroxy-1-naphthaldehyde)-2,6-pyridinedicarboxylic acid hydrazone (H-NP1) was synthesized and structurally characterized. UV-Vis and luminescent titrations of H-NP1 with F− demonstrated the presence of an H-NP1⋯F− interaction species with association constant log K# = 5.26 ± 0.01. The sensor responded to fluoride ion through an excited-state intermolecular proton transfer (ESPT) mechanism with the emission band red-shifted and enhanced. For further studying the potential mechanism, binding-signaling transduction of related compound H-NP2, bis(2-hydroxy-1-naphthaldehyde)-1,3-benzenedicarboxylic acid hydrazone and two control compounds (H-NP3) and (H-NP4) derived from 1-naphthaldehyde was also investigated for comparison.

Lanthanide heterometallic molecular squares Ru2–Ln2 exhibiting sensitized near-infrared emission

New lanthanide heterometallic molecular squares functionalized with Ru-bipy antenna chromophore Ru2-Ln2 exhibit sensitized near-infrared emission upon photo-excitation of the Ru-centered antenna at 420 nm.

Ligand-to-metal ratio controlled assembly of nanoporous metal–organic frameworks

Two bilayered metal-organic frameworks with nanoporous channels were synthesized at different ligand-to-metal ratios, which demonstrated an interesting crystal-to-crystal transformation property and a special fluorescent response to the different guest molecules included.

Three coordination polymers with helical chains based on methylenediisophthalic acid (H4MDIP)

Based on methylenediisophthalic acid (H4MDIP), three novel coordination polymers {[Mn2(MDIP)(bime)(H2O)2]2·2H2O}n (1) [bime = 1,2-ethanediylbis(imidazole)], {[Mn3(HMDIP)2(H2O)4]·4,4′-bipy·3H2O}n (2) [4,4′-bipy = 4,4′-bipyridine], and {[Co5(MDIP)2(H2O)6(μ-OH)2]·7H2O}n (3) have been synthesized and characterized by IR spectra, single-crystal X-ray diffraction analyses and thermal stability studies. The introduction of the bime and 4,4′-bipy ligands into Mn(CH3COO)2·4H2O and H4MDIP system leads to the formation of complexes 1 and 2, and the absence of the second ligand in the Co(NO3)2·6H2O and H4MDIP system leads to shape complex 3. Complex 1 is a 3D architecture with [Mn(–OCO–)]∞ helical chain. Coordination polymer2 is a 2D sheet structure with trinuclear unit, in which two kinds of 21 helical chains ([Mn(IP)]∞ (IP = isophthalic acid) and [Mn(MDIP)]∞) are included. Complex 3 exhibits the 3D porous structure with a pentanuclear cobalt unit in which a 1D shallow helical chain of hydrogen-bonded water molecules is shaped. From the topology point of view, complex 1 exhibits a (4,6)-connected network with the Schlafli symbol (42.63.8)2(44.62.74.84.9), complex 2 displays a (3,6)-connected network with CdI2 topology, and complex 3 displays a (4, 8)-connected network with Schlafli symbol (44.62)2(416.612) which is a decorated scu net.