Li-Ya Wang

Ancillary ligand-mediated syntheses and fluorescence properties of zinc(II) complexes based on flexible benzene dicarboxylic acid

This work presents a well-defined synthetic system exemplifying the effect of N-donor ancillary ligands on the formation of complex architectures in a zinc(II)-H2hmph-H2O system by the mild hydrothermal route (H2hmph = homophthalic acid). The single-crystal X-ray diffractions reveal that structure variation of isolated three complexes spans the range of dimensionalities from 2D lamella [Zn(hmph)(bpe)]n (1), 2D thick-layer [Zn(hmph)(bpp)]n (2) to 3D microporous framework {[Zn2(hmph)(trz)2]·H2O}n (3), showing the marked sensitivity of the structures to the flexibility of varied N-donor ancillary ligands (bpe = 1,2-di(4-pyridyl)ethylene, bpp = 1,3-di(4-pyridyl)propane, and Htrz = 1,2,4-triazole). The structures of three complexes can be considered as the assembly of various chain-like structure motifs. The 2D lamella structure of 1 features hmph-bridged binuclear zinc(II) chains joined by less flexible trans-bpe ligands, whereas the 2D thick-layer of 2 manifests hmph-bridged mononuclear zinc(II) chains cross-linked further by flexible bpp legands along two different directions. The alternate opposite chiral helixes, featuring rigid trz-bridged mononuclear zinc(II), and additional binuclear zinc(II) units are cohered together by hmph linkers yielding a 3D microporous coordination network of 3 with new framework topology. It is shown that the structures, packing densities, and thermal stabilities of all these complexes are markedly sensitive to the molecule size, conformation, and flexibility of varied N-donor ancillary ligands. Furthermore, fluorescence properties of complexes 1–3 are also investigated.

Structural and fluorescent regulation of Cd(II) coordination polymers with homoterephthalate by N-donor second ligands

This work reports the synthesis and fluorescence of a series of five Cd(II) coordination polymers with a variety of structure topologies. Homoterephthalic acid (H2htpa) reacts with Cd(OAc)2 to produce the coordination polymer [Cd(htpa)(H2O)]n (1). If a kind of dipyridyl-type second linear ligand is introduced into the synthetic system, three interpenetrating complexes are isolated, namely, [Cd(htpa)(bpp)]n (2), [Cd(htpa)(bpe)]n (3), and [Cd3(htpa)2(bpa)2(OAc)2]n (4) (bpp = 1,3-di(4-pyridyl)propane, bpe = 1,2-di(4-pyridyl)ethylene, and bpa = 1,2-bi(4-pyridyl)ethane), whereas the use of a circular second ligand, 1,2,4-triazole (Htrz), leads to a porous 3D framework {[Cd3(htpa)(trz)3(OAc)(H2O)4]·4H2O}n (5). Complex 1 has parallel Cd–O inorganic chains linked further by the htpa ligands forming individual 2D Cd(II)–carboxylate layers, complex 2 features the parallel interpenetration of two coincident 44 net sheets producing an overall 2D → 2D entanglement topology, complex 3 displays the inclined interpenetration of two sets of parallel corrugated 44 net sheets giving an overall 2D → 3D entanglement topology, complex 4 displays the normal interpenetration of three pcu nets affording an overall 3D → 3D entanglement topology, and complex 5 is characterized as Cd–triazolate layers cohered further by carboxylate linkers affording a single (3,5)-connected 3D open-framework (gra topology) with H-bonding water chains encapsulated in the cavities. The five complexes display a wide range of fluorescent emission behaviors, which are tentatively related with the local ligand environments with the different degrees of inter-chromophore coupling.

Three series of MOFs featuring various metal(II)-carboxylate chains cross-linked by dipyridyl-typed coligands: synthesis, structure, and solvent-dependent luminescence

This work presents seven M(II) metal–organic frameworks (MOFs) with three types of topology, which are hydrothermally synthesized by using a mixed ligand system including a functional group substituted phthalate (CF3-H2bdc or F4-H2bdc) and a dipyridyl-typed molecule (bpy, bpp, bpa, and bpe) (CF3-H2bdc = 4-(trifluoromethyl)phthalic acid, F4-H2bdc = tetrafluorophthalic acid, bpy = 4,4′-dipyridyl, bpp = 1,3-di(4-pyridyl)propane, bpa = 1,2-bis(4-pyridyl)ethane, and bpe = 1,2-di(4-pyridyl)ethylene). All these complexes display 3D MOFs featuring various metal(II)-carboxylate chains cross-linked further by dipyridyl-typed coligands. 1/1a serial possesses Cd(II)-carboxylate 21 helices forming the uninodal 5-connected nets with sev-5-Cccm topology, 2/2a serial contains Co(II)-carboxylate spiral-like chains assembling into the uninodal 5-connected nets with 5/4/t47 topology, and 3/3a/3b serial consists of Cu(II)-carboxylate 21 helices affording the uninodal 4-connected nets with a new framework topology (designated as lyu-3 here). Note that 1 undergoes a slight framework contraction in a single crystal to a single crystal form upon dehydration, whereas the framework expansion occurs in a single crystal to powder form upon rehydration. Interestingly, such reversible dehydrated–rehydrated behaviour is accompanied evidently by a rarely observed fluorescent transformation between 500 nm and 425 nm.

Three Zn(II) metal–organic frameworks assembled from a versatile tecton 5-ethyl-pyridine-2,3-dicarboxylate and dipyridyl-type coligand

Solvothermal reactions of 5-ethyl-pyridine-2,3-dicarboxylic acid and dipyridyl-type ligands with Zn(Ac)2·2H2O afford three metal–organic frameworks, including {[Zn2(EPDA)2(BPP)2]·(H2O)}n(1), [Zn3(EPDA)2(HEPDA)2(BPE)]n (2) and [Zn3(EPDA)2(HEPDA)2(BPA)]n (3) (H2EPDA = 5-ethyl-pyridine-2,3-dicarboxylic acid, BPP = 1,3-di(4-pyridyl)propane, BPE = 1,2-di(4-pyridyl)ethylene and BPA = 1,2-bi(4-pyridyl)ethane). The pronounced structure for 1 represents a rare 2D → 3D interpenetrated framework with new layer motif featuring a 4-connected net signified as Schlafli symbol of (3.64.8)(32.6.72.8). Complexes 2 and 3 possess intimately related structures featuring infinite Zn carboxylate layers of [Zn3(EPDA)2(HEPDA)2]n pillared by a BPE (or BPA) molecule to produce the three-dimensional frameworks with pcu topology based on the Zn trimers as the 6-connected nodes. It is shown that the flexible degree of dipyridyl-type molecules plays a key role for the assembly of diversified coordination networks. Furthermore, thermal degeneration and fluorescence properties of all three complexes are also investigated.

A novel metal–organic framework displaying reversibly shrinking and expanding pore modulation

A dynamically breathable microporous metal–organic framework was solvothermally synthesized and tested by the combination of X-ray diffractions and TG analysis techniques, unambiguously indicating that a reversible dehydration–rehydration process is accompanied by evident contraction and expansion of the pores without losing framework integrity.

Two topologically new trinodal cobalt(II) metal–organic frameworks characterized as a 1D metallic oxide and a 2D → 3D penetrated porous solid

Two novel Co(II) metal–organic frameworks, {[Co2(OH)(cnp-ipa)(EtOH)(H2O)]}n (1) and {[Co3(cnp-ipa)2(bpa)4(H2O)2]}I (2) (Hcnp-H2ipa = 5-(4-carboxy-2-nitrophenoxy)isophthalic acid, bpa = 1,2-bis(4-pyridyl)ethane), have been prepared and characterized. The single crystal X-ray diffractions reveal that both MOFs exhibit 3-nodal networks with new topological prototypes. MOF 1 possesses a (5,6,8)-connected 3D lattice with a new {32.44.54}2{34.44.54.63}{34.48.56.69.8} topology, and MOF 2 manifests a 2D → 3D interpenetrated porous solid featuring a (3,4)-connected layer lattice with a new {5.64.8}2{52.6}2{54.82} topology. The results illustrate the presence of a N-donor co-ligand to identify the assembly of MOFs. The solid-state properties such as the thermal stability and magnetic properties have also been studied.

Structural Diversity and Fluorescence Regulation of Three ZnII Coordination Polymers Assembled from Mixed Ligands Tectons

By adopting a mixed-ligand strategy, three ZnII coordination polymers were prepared by hydrothermal reactions of zinc(ii) acetate with flexible 1,2-phenylenediacetic acid (H2phda) combining with three nitrogen-rich tectons namely, [Zn2(phda)2(bpo)2]n·2H2O (1), [Zn(phda)(pytz)]n (2), and [Zn(phda)(bib)]n·H2O (3) (where bpo = 2,5-bis(4-pyridyl)-1,3,4-oxadiazole, pytz = 3,5-di(4-pyridyl)-1,2,4-triazole, and bib = 1,4-bis(imidazol-1-yl)benzene). The single-crystal X-ray diffraction patterns reveal that the three compounds contain metal(ii)-carboxylate chains further extended by such nitrogen-rich co-ligands to afford a vast diversity of structures from two-dimensional (2D) stepwise grids (1), 2D double layers (2), to three-dimensional (3D)→3D 4-fold interpenetrating diamondoid networks. Furthermore, the structural differences in these complexes are primarily affected by the introduction of N-donor ancillary co-ligands so that their solid-state photoluminescence properties exhibit various emission spectra. Especially, compound 3 shows a guest-sensitive luminescence behaviour, which may be useful in applications as guest sensors.