Li-Min Zheng

A cryogenic luminescent ratiometric thermometer based on a lanthanide phosphonate dimer

The first example of a ratiometric Eu/Tb thermometer based on a lanthanide phosphonate is reported, which presents a temperature dependent emission under 393 nm excitation that enables its use as a molecular thermometer with a maximum relative sensitivity of 3.9% K−1 and a minimum temperature uncertainty of 0.15 K, both at 38 K. Additionally, the compound is a competitive luminescent colorimetric probe showing temperature dependent (x, y) CIE color coordinates changing from yellow, (0.48, 0.48) at 18 K, to red, (0.64, 0.37) at 300 K.

Synthesis, structure and magnetic behavior of a di-μ-chloro-di-μ-imidazolato-tetracopper(II) complex with two dinucleating macrocycles

Abstract The synthesis, crystal structure and magnetic behavior of the di-μ-chloro-di-μ-imidazolato-tetracopper(II) complex [L2Cu4(Im)2Cl2](ClO4)4(CH3OH), where Im is imidazole and L is 3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,13]triaconta-1(29),11(30),12,14,25(26),27-hexaene, have been studied. X-ray structure analysis shows that the compound crystallizes in monoclinic and space group P2(1)/c, with a=13.716(3), b=11.165(2), c=27.340(6) A, β=98.43(3)° and Z=2. The cation consists of two imidazolate bridged dicopper(II) centers encapsulated within two macrocycles, respectively, which are linked by a pair of chloride atoms. In each imidazolate bridged dicopper(II) center, both copper atoms are five-coordinated by four basal nitrogen atoms (three from the macrocycle and one from the imidazolate) and one axial chloride atom shared with another copper atom in the other imidazolate bridged dicopper(II) center in the molecule. pH-dependent ESR studies of the title complex in frozen 50% aqueous DMSO solution show that the bridged cation [LCu2(Im)]3+ exists as a major species in solution over the range 7.00≤pH≤11.5, and the μ-Im bridge is broken in the pH range of 7.00–5.20. The molar conductance of the title complex indicates that the μ-Cl bridge is almost entirely dissociated when dissolved in 1:1 DMSO aqueous solution. However, when Cl− ions were gradually added to the solution, a complex with a CuN4Cl chromophore was successively formed. Magnetic measurement studies on the powder sample reveal that antiferromagnetic interactions are mediated through both μ-Im (J1=−26.78 cm−1) and μ-Cl (J2=−9.52 cm−1) bridges.

Synthesis, characterization and in vitro anticancer activity of the biomolecule-based coordination complex nanotubes

Biomolecule-based coordination complex nanoassemblies are a new type of functional materials that are attracting increasing attention. They could possess functionalities that are not readily attainable with other materials, and represent a promising research area that can be exploited in coordination chemistry and materials science. Using bioactive folic acid molecule as a linker, Ni-folate-hydrazine coordination complex nanotubes (CCNTs) have been effectively constructed using the solvothermal method. This is not only the first example of the CCNTs being formed using a nonpyridyl-based molecule as a linker, but also the first report on biomolecule-based CCNTs (BMB-CCNTs) with anticancer activity. It does not require any post treatment to achieve targeted delivery and biocompatible performance. The BMB-CCNTs are sufficiently stable at normal pH of 7.4 until it enters a tumor cell, subsequently it breaks open to release drug in the tumor cell. Furthermore, it overcomes the major limitations of antibody-drug and folate-drug conjugates and is a potential smart multi-functional nanomedicine system. The results of in vitro cytotoxicity assay reveal that the antitumor ability of BMB-CCNTs is similar to cisplatin (CDDP), while their cytotoxicity for normal cells is lower than the latter. Furthermore, BMB-CCNTs exhibit excellent performance as drug carriers and target agents for delivering drugs into tumor cells. Bio-TEM and confocal laser scanning microscope images trace the uptake process of CDDP-CCNTs by a tumor cell. CDDP-CCNTs exhibit dual anti-cancer effect.

Modulating the microporosity of cobalt phosphonates via positional isomerism of co-linkers

By incorporating co-ligands 1,2-bis(imidazol-1-ylmethyl)benzene (1,2-bix), 1,3-bis(imidazol-1-ylmethyl)benzene (1,3-bix) and 1,4-bis(imidazol-1-ylmethyl)benzene (1,4-bix), three isomeric cobalt phosphonates Co5(1,2-bix)2(pbtc)2(H2O)4·8H2O (1), Co5(1,3-bix)2(pbtc)2(H2O)4·7.5H2O (2), and Co5(1,4-bix)2(pbtc)2(H2O)4·6H2O (3) (pbtcH5 = 5-phosphonatophenyl-1,2,4-tricarboxylic acid) have been isolated successfully. Compound 1 shows a layer structure in which chains containing alternately arranged Co3O2 trimers and Co2 dimers are connected by pbtc5− ligands. The 1,2-bix co-ligand adopts a cis-mode, and coordinates to the cobalt atoms from the same chain. Upon dehydration, compound 1 undergoes single-crystal-to-single-crystal (SC–SC) structural transformation forming a new crystal phase Co5(1,2-bix)2(pbtc)2(H2O)4 (1a). The process is reversible upon rehydration, showing a breathing effect. In compounds 2 and 3, similar layers composed of cobalt phosphonate chains and pbtc5− linkages are also found, which are further cross-linked by 1,3-bix or 1,4-bix to form 3D framework structures. The three compounds show different microporosities, as confirmed by their different N2 gas adsorption behaviors.

Homochiral metal phosphonate nanotubes

A new type of homochiral metal-organic nanotubular structures based on metal phosphonates are reported, namely, (R)- or (S)-[M(pemp)(H2O)2][M = Co(II) (1), Ni(II) (2)] [pemp(2-) = (R)- or (S)-(1-phenylethylamino)methylphosphonate]. In these compounds, the tube-walls are purely inorganic, composed of metal ions and O-P-O bridges. The cavity of the nanotube is hydrophilic with one coordination water pointing towards the center, while the outer periphery of the nanotube is hydrophobic, decorated by the phenylethyl groups of pemp(2-). The thermal stabilities, adsorption and proton conductivity properties are investigated.

Synthesis, crystal structure and property of a novel azide-bridged one-dimensional chain copper(II) complex with a dinucleating macrocyclic polyamine

An azide-bridged polymeric cationic chain complex, [LCu2(N3)2]n(ClO4)2n·n(H2O)**, where L=the dinucleating macrocyclic ligand bis-p-xylylBISDIEN, has been prepared and characterized by x-ray crystallography, u.v.-vis and i.r. spectra, and by magnetic measurements. The structure consists of cationic azide-bridged [LCu2(N3)2]2+ (unit) chains, non-coordinated perchlorate anions and crystallized water molecules. The azide anion is bound to two copper atoms in neighboring units with an end-to-end bridging mode. In each unit, the copper atoms have a different coordination geometry; Cu(1) is a four-coordinated, distorted square-planar geometry, whereas Cu(2) is a five-coordinated, distorted square-pyramid. The electronic spectra of the title complex differ in anhydrous and in aqueous MeCN solutions, indicating that dissociation and solvation occur in aqueous solutions. The characteristic i.r. absorptions of azides and perchlorates are described. Magnetic moments vary from 2.05 (B.M.) at 300K to␣2.01 (B.M.) at 80K, which suggests that very weak interactions exist between the metals.

A pH responsive electrochemical switch sensor based on Fe(notpH3) [notpH6 = 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylene-phosphonic acid)]

The electrochemistry of a macrocyclic metal complex Fe(notpH(3)) [notpH(6)=1,4,7-triazacyclononane-1,4,7-triyl-tris(methylene-phosphonic acid)] reveals that the protonation/deprotonation of the non-coordinated P-OH groups in Fe(notpH(3)) affects its formal potential value (E(0)) considerably. Plotting E(0) as function of solution pH gives a straight line with a slope of -585 mV pH(-1) in the pH range of 3.4-4.0, which is about ten times larger than the theoretical value of -58 mV pH(-1) for a reversible proton-coupled single-electron transfer at 20 °C. A sensitive pH responsive electrochemical switch sensor is thus developed based on Fe(notpH(3)) which shows an on/off switching at pH ∼ 4.0.

Structure and magnetic properties of a new dinuclear nickel(II) complex with a dinucleating hexaazamacrocycle

The crystal structure and magnetic properties of a new dinuclear nickel(II) complex [LNi2(AcO)4]·14H2O, where L = 3,6,9,17,20,23-hexaazatricyclo [23.3.1.111,13] triaconta-1(29),11(30),12,14,25(26),27-hexene, has been studied. X-ray structure analysis shows that the compound consists of a discrete [LNi2(AcO)4] complex and 14 lattice water molecules. Each Ni atom is six coordinated by three N atoms from the macrocycle and three O atoms from the two coordinated acetates; two nickel atoms in each macrocycle are at the distance of 7.028Å. The result of the magnetic measurement indicates that the zero-field splitting constant of nickel(II) centres |D| = 1.87 cm−1.

Racemic cobalt phosphonates incorporating flexible bis(imidazole) co-ligands

By incorporating flexible bis(imidazol-1-ylmethyl)benzene (bix) co-ligands, four new racemic cobalt phosphonates with formulae Co3(3-ppap)2(1,4-bix)2(H2O)4·4H2O (1), Co3(3-ppap)2(1,3-bix)2(H2O)4·5H2O (2), Co3(3-ppap)2(1,2-bix)2(H2O)4·4H2O (3) and Co3(ppa)2(1,2-bix)2·4H2O (4) are isolated, where 3-ppapH3 represents 3-phenyl-3-((phosphonomethyl)amino)propanoic acid and ppaH3 is 2-phenyl-2-(phosphonomethylamino)acetic acid. Compounds 1-3 crystallize in the monoclinic space group P21/c and show two-dimensional structures in which the Co3(3-ppap)2 chains are bridged by 1,4-bix, 1,3-bix and 1,2-bix ligands in trans-modes, respectively. Within the chain, a racemic dimer of Co2(3-ppap)2(2-) is found, where the Co atoms are doubly bridged by O-P-O units from the (S)- and (R)-3-ppap(3-) ligands. The dimers are connected by another crystallographically independent Co atom through O-P-O linkages to form an infinite racemic chain. The packing modes of the layers in 1-3 are quite different, however, which are ABAB in the cases of 1 and 3 while ABCDABCD in the case of 2, attributed to the positional isomerism of the bix co-ligands. Compound 4 displays a chain structure in which the 1,2-bix bridges the Co atoms in cis-mode within the chain. Magnetic properties are investigated for all compounds.