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In this work, three novel Zn(ii)-CPs with diverse structures and fascinating topologies can be highly selective and sensitive luminescent sensors for detection of Fe3+.

Five CPs have been synthesized by a new semi-rigid dicarboxyl ligand and neutral ligands under hydrothermal conditions, and their luminescent sensing experiments for different small molecules/ions were studied in detail.

A series of isomorphic lanthanide coordination polymers with 2,6-dimethylpyridine-3,5-dicarboxylic acid (H2mpda), formulated as [Ln(Hmpda)3(H2mpda)] [Ln = Tb (1), Eu (2), Gd (3) and Ln = mixed lanthanide (4)], have been synthesized and structurally characterized. Single-crystal X-ray diffraction reveals that they are isomorphic and each displays a 1D chain-based structure, which can be expanded by hydrogen bond interactions into a 3D supramolecular architecture. In addition, they are thermally stable up to 350 °C and unusually chemically stable in a wide pH range of 2–13, which was confirmed by variable temperature XRD and pH dependent XRD. Meanwhile, the luminescence properties of compounds 1–4 are investigated. Of these, compound 1 acts as a luminescent probe for the sensing of temperature and pH, and compound 4 shows white light emission. Moreover, compounds 1, 2 and 4 were encapsulated in LED devices, with compound 4 exhibiting warm white light emission with excellent color rendering index (CRI) and correlated color temperature (CCT).

In this work, water- and temperature-induced single-crystal-to-single-crystal (SCSC) transformation and dissolution–recrystallization structural transformation (DRST) are observed among three new copper(II) coordination polymers, {[Cu5(μ3-OH)2(MIPA)4(4,4′-bpy)2]·2H2O}n (1), {[Cu(H2O)2(MIPA)(4,4′-bpy)0.5]·H2O}n (2) and {[Cu2(H2O)2(MIPA)2(4,4′-bpy)(μ2-H2O)]·3H2O}n (3) (MIPA = 4-methoxyisophthalic acid, 4,4′-bpy = 4,4′-bipyridine). The 3D framework of 1 experienced an intensive DRST process to form the 1D intermediate of 2, followed by a unique SCSC process to transform it into the 2D network of 3. Nevertheless, compound 3 can be obtained from compound 1 directly via another DRST. That is to say, a DRST process could be achieved by the combination of another DRST process and an SCSC process. To the best of our knowledge, this type of study is still scarce. And it provides a convenient strategy to investigate the mechanism of crystal transformation and construct advanced crystalline materials. Results have been characterized by single crystal X-ray diffraction and powder X-ray diffraction (PXRD). Significant structural alterations were observed and these changes could be analyzed from the properties of center Cu(II) ions and the switch of chelating-bridging modes of MIPA. Magnetic susceptibility measurements indicate that 1 and 3 exhibit antiferromagnetic interaction between adjacent Cu(II) centers. Additionally, complexes 1–3 have been characterized by thermogravimetric analysis and infrared and PXRD studies.

Starting from the pentagonal bipyramidal single-ion magnet [Co(tdmmb)(H2O)2][BF4]2 and a series of linear bridging ligands of different lengths, three new cobalt(II) one-dimensional (1D) coordination polymers, [Co(tdmmb)(pyz)][BF4]2·CH3CN·H2O (1), [Co(tdmmb)(apy)][BF4]2·2CH3CN (2), and [Co(tdmmb)(bpe)][BF4]2·3CH3CN (3) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetra-aza[3](2,6)pyridino[3](2,9)-1,10-phenanthrolinophan-2,10-diene) (pyz = pyrazine) (apy = 4-aminopyridine) (bpe = 1,2-di(4-pyridyl)ethane)), have been synthesized and characterized structurally and magnetically. Symmetric ligands pyz and bpe result in the nearly linear chains in 1 and 3, while the asymmetric ligand apy leads to the zig-zag chain in 2. As the length of the ligands increases, the intrachain Co⋯Co distance also increases, i.e. 7.56, 7.70, and 13.85 A for 1–3, respectively. Magnetic investigation revealed the gradual decrease in the magnetic interactions between the Co2+ ions from 1 to 3, along with the increase in the intrachain Co–Co distances. Due to the existence of the weak antiferromagnetic (AF) interaction, the SIM behavior of the starting material is surpressed in compounds 1 and 2, and they show a simple paramagnetic behavior. While for 3, field-induced slow magnetic relaxation was observed at a low temperature with an energy barrier of Ueff = 19 K. This observation suggests that the magnetic interaction between the Co2+ centers in 3 is negligible, consistent with the very long Co–Co distance in 3. These 1D compounds are rare chain compounds composed of metal centers with a nearly D5h symmetry. Notably, compound 3 is the second example of a 1D Co(II) chain compound displaying a SIM behaviour. These studies illustrated that the magnetic interaction between the SIMs can be used to tune slow magnetic relaxation.

Six new highly symmetrical and isostructural 3D lanthanide metal–organic frameworks (Ln-MOFs) {[Ln2(Ccbp)3·6H2O]·3Cl−·4H2O} Ln = Tb (1), Eu (2), Gd (3), Sm (4), Er (5) and Yb (6), Ccbp− = 4-carboxy-1-(4-carboxybenzyl)pyridinium, and the mixed Ln-MOF {[Tb1.828Eu0.172(Ccbp)3·6H2O]·3Cl−·4H2O} (7) have been successfully synthesized and fully characterized. The complex 1 was utilized as a representative chemosensor to detect small molecules, cations and anions, respectively. Interestingly, 1 exhibited dual-functional detection of Pb2+ and Fe3+ ions in ethanol with excellent linear variation to quantify the corresponding concentration change. In addition, the temperature-dependent luminescence properties of 1, 2 and 7 have also been investigated systematically, which demonstrated that both 1 and 7 have potential to quantitatively detect temperature as a luminescent thermometer over a wide range from 10–300 K for 1 and 10–170 K for 7. Thus, the as-obtained Ln-MOF materials have potential to serve as the first examples of a multifunctional luminescent sensor for quantitatively detecting the temperature (10–300 K) and the concentration of Pb2+ and Fe3+ ions in ethanol solution.

Branched α-MnO2 nanorods are synthesized using a facile hydrothermal method without surfactants or templates. The formation of α-MnO2 with different morphologies, including branched nanorods and nanorods with controllable length, is achieved by controlling the starting concentration of reactants. The morphology and structure of the branched α-MnO2 nanorods are fully characterized and the growth mechanism is proposed based on the experimental observation. The novel structures presented here enrich the nanoscale community of α-MnO2 materials, thus enabling greater potential applications. The electrochemical properties of as-synthesized branched α-MnO2 nanorods are also studied by cyclic voltammetry (CV) and galvanostatic charge/discharge measurement. The branched α-MnO2 nanorod electrode shows a high specific capacitance of 182 F g−1 at a current density of 2 A g−1, with a good rate capability (72.5% at 64 A g−1) and excellent cycling stability.

A special core/shell/shell structured NaYF4/NaYF4:Yb3+,Er3+/NaYF4 (CSS) nanocrystal was designed to ensure each luminescence center in the emitting shell had the same surroundings. The nanocrystal includes a support core NaYF4 nanoparticle in the center coated by a thin emitting shell NaYF4:Yb3+,Er3+ and another NaYF4 shell with adjustable thickness as the outer shielding shell. The green upconversion fluorescence intensity Ig(d) of the CSS nanoparticles shows an exponential relationship with the thickness d of the shielding shell. When d decreased to 0, Ig(0) was ~356 times smaller than Ig(∞) due to the drastic fluorescence quenching of the rare earth luminescence centers by the surroundings. Our experimental results indicate that ~90% of the severe effect of the surroundings can be eliminated by coating with a ~4 nm-thick NaYF4 shielding shell.

ZnO nanoparticles are among the most promising emerging fluorescent labels for cellular imaging. However, there are only a few reports on the successful application of ZnO nanoparticles in biolabeling so far. The major problem of ZnO nanoparticles arises from their poor stability in water. In this work, two new facile synthesis methods were developed for fabricating water-stable ZnO nanoparticles, which have blue and yellow fluorescence and are expected to be of use for labeling different cellular structures simultaneously. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), UV-vis, and fluorescence spectrophotometry (PL) were employed to investigate the structures and properties of ZnO nanoparticles. The mechanisms for the formation of the ZnO nanoparticles of both samples are analyzed. Furthermore, hemolysis assay was performed to evaluate the biocompatibility of these ZnO nanoparticlesin vitro. The biocompatibility of the ZnO nanoparticles, even at very high doses, ensures their potential in biomedical applications.

ZnO:MgO nanocrystals have been synthesized by a sequential preparative procedure and capped with γ-Aminopropyl triethoxysilane (APTES), thereby rendering the surface of the nanocrystals hydrophilic and the particles water-soluble. Orthogonal experiment was employed to optimize the correlated parameters of the reaction of capping ZnO:MgO nanocrystals with APTES. The effects of the quantity of APTES, reaction time, and reaction temperature on the aqueous stability of APTES-capped ZnO:MgO nanocrystals were investigated by orthogonal experiment and their optimal values were determined to be: 0.25 mmol, 60 min, and 25 °C, respectively. The water-soluble APTES-capped ZnO:MgO nanocrystals emit strongly in the visible region on excitation by UV radiation and are stable over extended periods. The aqueous-stability of the nanocrystals is attributed to the exposed hydrophilic groups (–NH2, –OH). Furthermore, hemolysis was performed to evaluate the biocompatibility of the nanocrystals. Hemolytic results indicate that APTES-capped ZnO:MgO nanocrystals have good biocompatibility, which is especially important for ensuring their potential in biomedical applications.

ZnO nanocrystals with strong blue emission have been synthesized via a facile polyol hydrolysis route. The as-synthesized ZnO nanocrystals were stable in water, even at basic or acidic aqueous conditions. The water stability of such ZnO nanocrystals was provided by the hydroxyl groups of triethylene glycol (TREG) and also the carboxyl group of oleic acid (OA) on their surfaces. We found that heat temperatures, heat times and concentrations of OA were all important factors that influence the particle size and the crystallinity of the ZnO nanocrystals. Interestingly, the photoluminescence properties of ZnO nanocrystals were not dependent on the particle size, but were attributed to the surface defects on ZnO which were closely related to the process of ZnO nanocrystals coated by TREG. Such ZnO water-disperse nanocrystals with intense blue fluorescence are expected to be of use for further practical applications, such as for the applications in biological fluorescence labelling.

Three 3d–4f heterometallic complexes, namely, [Co3Ln2(L)4(C2O4)2(H2O)2·6H2O]n (Ln = Pr (1), Nd (2), Sm (3); H2L = benzimidazole-5,6-dicarboxylic acid, H2C2O4 = oxalic acid), have been synthesized hydrothermally and characterized by single crystal X-ray diffraction study, IR, TGA and elemental analysis. The three complexes are isostructural; in their structures, the Co(II) centers are connected into a linear Co3 cluster by the C2O42− anions, the Ln(III) centers are connected into one-dimensional (1D) {Ln–O–C}n rod-like chains by the carboxyl groups of L2− anions, the linear Co3 clusters and {Ln–O–C}n rod-like chains are further connected by the L2− anions, and finally construct three 3D frameworks, which contain 1D channels along the b direction occupied by (H2O)8 clusters. In addition, magnetic studies of the three complexes all reveal antiferromagnetic behaviors.

Reactions of Co(II) salts with rigid 5-amino-isophthalic acid (AIP) and flexible bis(imidazole) ligands by controlling the metal–ligand ratio gave rise to two pairs of new complexes: [Co(AIP)(bimb)] (1) and [Co(AIP)(bimb)0.5] (2), [Co(AIP)(bix)]·H2O (3) and [Co2(AIP)2(bix)1.5] (4) (bimb = 1,4-bis (imidazol-1-yl)-butane, bix = 1,4-bis(imidazol-1-yl-methylene)-benzene). Comparative study revealed that the different metal–ligand ratios affected the coordination modes of the ligand and thus resulted in four different structures. All complexes display 2D structures and extend into 3D supramolecular frameworks via intermolecular hydrogen bonds. Complex 1 features a (4,5)-connected hydrogen-bond network. Complex 2 displays a 2D bilayered structure with a rare (3,4)-connected (63)(65 ·8) topology. Complex 3 is an 2D (4,4) network showing 2-fold parallel interpenetrating 2D → 2D structure, which features the 2-fold interpenetrating cds hydrogen-bond net. Complex 4 shows a trinodal (4,4,5)-connected hydrogen-bond net. Magnetic studies of 1 reveal ferromagnetic interaction at low temperature and 4 displays antiferromagnetic behavior.

A new nickel complex, [Ni(pim)(bibp)1.5(H2O)]·1.25H2O (1, pim = pimelic acid, bibp = 4,4′-bis(1-imidazolyl)biphenyl), was obtained via hydrothermal synthesis. The complex shows an unprecedented 2D→3D net with the coexistence of polycatenation and polythreading based on the T-shaped bilayer motifs.

Five novel metal–organic frameworks (MOFs) have been hydrothermally synthesized, namely, [Co(bimb)(2,4′-bpdc)(H2O)2]·H2O (1), [Co2(bimb)3(2,4′-bpdc)2(H2O)2]·H2O (2), [Co(bix)(2,4′-bpdc)] (3), [Co(bix)0.5(2,4′-bpdc)(H2O)0.25] (4) and [Co(bimh)(2,4′-bpdc)] (5), based on mixed ligands, 2,4′-biphenyldicarboxylic acid (2,4′-H2bpdc) as organic linkers and different bis(imidazole) ligands as co-ligands: (1,4-bis(imidazol-1-yl)-butane (bimb), 1,4-bis(imidazol-1-yl-methylene)-benzene (bix) and 1,6-bis(imidazol-1-yl)-hexane (bimh)). The coordination polymers were characterized by single-crystal X-ray diffraction, thermogravimetric analysis (TGA) and element analysis (EA). Reactions between CoCl2·6H2O, 2,4′-H2bpdc and neutral bimb ligand afforded two crystallographically different coordination polymers (1 and 2) through tuning the ligand/metal ratio meticulously. Compound 1 crystallizes in a noncentrosymmetric Pna21 space group with 65·8 CdSO4-type topology, while compound 2 is isolated with P21/c space group and displays a 4-connected 66 network. By substituting bix for bimb ligand, alteration of the metal/ligand ratio in the initial reaction system induced a transition from 2D layer (compound 3) to 3D architecture (compound 4). Notably, the structure of 4 is constructed from [Co(2,4′-bpdc)] layers, which are further pillared by bix ligands into a 3D 3,4-connected (63)·(63·103) network. In 5, the left- and right-handed helical chains constructed by Co(II) and bimh ligands are bridged by 2,4′-bpdc2− anions to form a layer-like structure.

The factors that influence the decarboxylation of pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) under hydrothermal conditions were investigated. Higher temperature and lower pH are very effective promoters for the decarboxylation of H4pztc in the presence of ds-block metal ions. Four novel complexes of H4pztc and four complexes from the decarboxylation of H4pztc, [Zn2(pz25dc)(phen)4](NO3)2·10H2O (1), [Zn2(pztc)(phen)4]·12H2O (2), {[Zn2(pztc)(bpy)2(H2O)2]·2H2O}n (3), [Cu2(pz25dc)(phen)4](NO3)2·10H2O (4), {[Cu2(pztc)(bpy)2 H2O]·4H2O}n (5), [Cu2(H2pztc)(bpy)2(H2O)2](NO3)2·2H2O (6), [Cd(pz26dc)(phen)(H2O)2] (7) and [Cd(pz26dc)(bpy)(H2O)2] (8) (pz25dc = pyrazine-2,5-dicarboxylate, pz26dc = pyrazine-2,6-dicarboxylate, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridyl) have been synthesized and characterized by X-ray single crystal diffraction, elemental analysis, IR, thermal gravimetric analysis (TGA) and fluorescence measurement. 1, 2, 4 and 6 are dinuclear complexes bridged by pztc or pz25dc, 3 and 5 are 1D coordination polymers. In 6, the Cu(II) ions are bridged by bis-tridentate H2pztc2−. 7 and 8 are mononuclear Cd(II) complexes. The 2D or 3D supramolecular structures of 1–8 were built up by hydrogen bonds and π⋯π interactions. Notably, a novel T5(0)A0 water tape and a S-shaped (H2O)10cluster are observed in 2 and 5, respectively.

Pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) reacted with Ni(ClO4)2·6H2O and 1,10-phenanthroline (phen) in aqueous solutions to form two different complexes, [Ni(H2pztc)(phen)H2O]·H2O (1), [Ni(phen)3](H2pztc)·10.5H2O (2), under hydrothermal conditions and at room temperature respectively. In 1, Ni(II) ion is coordinated by tridentate chelated H2pztc2−. The carboxyl and carboxylate groups of H2pztc2− are roughly coplanar with the pyrazine ring and form intramolecular hydrogen bonds. While in 2, H2pztc2− remains uncoordinated, the carboxyl and carboxylate groups of H2pztc2− are out of plane of the pyrazine ring and do not form intramolecular hydrogen bonds. H2pztc2− and water molecules form negatively-charged channels and the channels are filled with [Ni(phen)3]2+ in the 3D supramolecular structure of 2. In addition, a novel water tape is present in 2.

Three novel lanthanide coordination polymers with large channels and water clusters, [Yb2(pztc)1.5(H2O)6]·7H2O (1), [Lu2(pztc)1.5(H2O)6]·7.5H2O (2) and [Er2(pztc)1.5(H2O)6]·7H2O (3), have been synthesized by the reactions of pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) and Ln(III) salts in aqueous solution at room temperature or under hydrothermal conditions, and characterized by X-ray crystallography, elemental analysis, IR, UV-vis and thermal gravimetric analysis (TGA). Single crystal X-ray diffraction determination indicates that the Ln(III) ions were coordinated by three tridentate cheated pztc4− ligands and bis-tridentate cheated pztc4− ligands bridged Ln(III) ions to form hexanuclear metal ring structures with nano-channels which were filled with (H2O)14clusters.