Biomedical subjects

Zhiping Zheng

Publications and source records attributed to Zhiping Zheng.

11 recordsLinked to original sources

PubMed2006

Dendritic arrays of [Re6(mu3-Se)8]2+ core-containing clusters: exploratory synthesis and electrochemical studies.

The reaction between the previously reported site-differentiated cluster solvate [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(MeCN)](SbF(6))(2) (1) with pyridyl-based ditopic ligands 4,4'-trimethylenedipyridine (2), 1,2-bis(4-pyridyl)ethane (3), and (E)-1,2-bis(4-pyridyl)ethene (4) afforded cluster complexes of the general formula [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(L)](SbF(6))(2) (5-7), where L represents one of the pyridyl-based ligands. Reacting these cluster complex-based ligands with the fully solvated cluster complex [Re(6)(mu(3)-Se)(8)(MeCN)(6)](SbF(6))(2) (8) produced dendritic arrays of the general formula {Re(6)(mu(3)-Se)(8)[Re(6)(mu(3)-Se)(8)(PEt(3))(5)(L)](6)}(SbF(6))(14) (9-11), each featuring six circumjacent [Re(6)(mu(3)-Se)(8)(PEt(3))(5)](2+) units bridged to a [Re(6)(mu(3)-Se)(8)](2+) core cluster by the pyridyl-based ligands. Electrochemical studies using a thin-layer electrochemical cell revealed cluster-based redox events in these cluster arrays. For 9 (L = 2), one reversible oxidation event corresponding to the removal of 7 electrons was observed, indicating noninteraction or extremely weak interactions between the clusters. For 10 (L = 3), two poorly resolved oxidation waves were found. For 11 (L = 4), two reversible oxidation events, corresponding respectively to the removal of 1 and 6 electrons, were observed with the 1-electron oxidation event occurring at a potential 150 mV more positive than the 6-electron oxidation. These electrochemical studies suggest intercluster coupling in 11 via through-bond electronic delocalization, which is consistent with electronic spectroscopic studies of this same molecule.

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PubMed2003

Hydrogen-bonded extended arrays of the [Re6(mu3-Se)8]2+ core-containing clusters.

Site-differentiated solvated clusters of the general formula [Re(6)(mu(3)-Se)(8)(PEt(3))(n)(MeCN)(6)(-)(n)](SbF(6))(2) (n = 4, cis and trans; n = 5) undergo ligand substitution reaction with isonicotinamide to afford the corresponding amide derivatives, [Re(6)(mu(3)-Se)(8)(PEt(3))(n)(isonicotinamide)(6)(-)(n)](2+) [1 (n = 5); 2 (n = 4, trans); 3 (n = 4, cis)]. Retention of stereochemistry in each case was confirmed by (1)H and (31)P NMR. The solid-state structures of all three compounds were established crystallographically, which revealed self-complementary hydrogen-bonding interactions between adjacent cluster units. While complex 1 exists as hydrogen-bonded dimers in the solid state, compounds 2 and 3 form one-dimensional chains of clusters bridged by paired hydrogen bonds. It is the rigid stereochemistry of the cluster, combined with the classic crystal engineering motif of complementary N-H.O amide hydrogen bonding, that affords the predictable solid-state structures and dimensionality.

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PubMed2003

Ligand-bridged oligomeric and supramolecular arrays of the hexanuclear rhenium selenide clusters--exploratory synthesis, structural characterization, and property investigation.

Transition metal clusters, by virtue of their well-defined structures and unique properties, present themselves as an attractive class of structural and functional building blocks for molecular and supramolecular construction. Summarized in this Account are highlights of our efforts utilizing face-capped octahedral [Re(6)(mu(3)-Se)(8)](2+) clusters as the fundamental building units to create a wide variety of preprogrammed architectures. These include molecular "Tinkertoys", featuring stereospecific cluster units bridged by multitopic ligands and extended arrays of clusters engineered via hydrogen bonding and secondary metal-ligand coordination.

Ligands↗

PubMed2002

Novel concentration-driven structural interconversion in shape-specific solids supported by the octahedral [Re(6)(mu3-Se)8]2+ cluster core.

A complex containing the face-capped octahedral [Re(6)(mu(3)-Se)(8)](2+) cluster core, cis-[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](SbF(6))(2) (1), is used as a ditopic ligand with an enforced right angle between the two 4,4'-dipyridyl moieties for the coordination of Cd(2+) ion. Two coordination polymers, [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](2)[Cd(NO(3))(2)]](SbF(6))(4).21C(4)H(10)O.21CH(2)Cl(2) (2) and [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)][Cd(NO(3))(3)]](NO(3)).2C(4)H(10)O.CH(2)Cl(2) (3), are obtained. The relative concentration of Cd(2+) determines which species is isolated, and the conversion of the first structure into the second is demonstrated experimentally.

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PubMed2002

Routes to metallodendrimers of the [Re(6)(mu(3)-Se)(8)](2+) core-containing clusters.

The reaction of [Re6(mu3-Se)8(PEt3)5(MeCN)](SbF6)2 with an excess of 1,2-bis(4-pyridyl)ethane (L1) and (E)-1,2-bis(4-pyridyl)ethene (L2) produced [Re6(mu3-Se)8(PEt3)5(L1)](SbF6)2 and [Re6(mu3-Se)8(PEt3)5(L2)](SbF6)2, respectively, each bearing an accessible pyridyl N atom capable of further metal coordination. Reacting these cluster complex-based ligands with [Re6(mu3-Se)8(MeCN)6](SbF6)2 afforded two heptacluster metallodendrimers, each featuring a central [Re6(mu3-Se)8]2+ cluster core surrounded by six units of [Re6(mu3-Se)8(PEt3)5]2+ via the bridging interactions of its respective dipyridyl-based ligands. Their identity and stereochemistry have been established, with the most convincing evidence furnished by a unique 77Se NMR spectroscopic study. Electrochemical studies suggest very interesting electronic properties of these novel metallodendrimers.

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PubMed2002

Built to order: molecular tinkertoys from the [Re(6)(mu(3)-Se)(8)](2+) clusters.

Ligand substitution of [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(CH(3)CN)](SbF(6))(2) (1) with pyridyl-based ligands, 2,4,6-tri-4-pyridyl-1,3,5-triazine (L1) and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (L2), produced respectively the star-shaped tricluster (T1) and tetracluster (T2) arrays, wherein three (T1) and four (T2) units of the [Re(6)(mu(3)-Se)(8)](2+) core-containing clusters are interconnected by the corresponding bridging ligands. These novel supramolecular assemblies were characterized by a combination of NMR ((1)H and (31)P) spectroscopy, ESI-MS, and microanalysis. The molecular and solid-state structures of T1 have also been established by single-crystal X-ray diffraction.

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PubMed2002

Halide-templated assembly of polynuclear lanthanide-hydroxo complexes.

A series of pentadecanuclear lanthanide-hydroxo complexes possessing a common core of the formula [Ln(15)(mu(3)-OH)(20)(mu(5)-X)](24+)(1, Ln = Eu, X = Cl(-); 2, Ln = Nd, X = Cl(-); 3, Ln = Gd, X = Cl(-); 4, Ln = Pr, X = Br(-); 5, Ln = Eu, X = Br(-)) were prepared by L-tyrosine-controlled hydrolysis of corresponding lanthanide perchlorates in the presence of added Cl(-) or Br(-). The cationic cluster core comprises five vertex-sharing cubane-like [Ln(4)(mu(3)-OH)(4)](8+) units centered on the halide template. In the case of templating I(-), dodecanuclear complexes were isolated instead. The core component, [Ln(12)(mu(3)-OH)(16)(I)(2)](18+) (6, Ln = Dy; 7, Ln = Er), consists of four vertex-sharing cubane-like [Ln(4)(mu(3)-OH)(4)](8+) units and exists as a square-shaped cyclic structure with one I(-) located on each side of the square plane. An analogous hydrolytic reaction involving Er(NO(3))(3), L-tyrosine, and NaOH affords the known hexanuclear complex [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))(2) whose core component is a face-capped octahedral [Er(6)(mu(6)-O)(mu(3)-OH)(8)](8+) cluster with an interstitial mu(6)-oxo group (Wang, R.; Carducci, M. D.; Zheng, Z. Inorg. Chem. 2000, 39, 1836-1837.). The efficient self-assembly of halide-encapsulating multicubane complexes (1-7) and the inability to produce an analogous nitrate-containing complex demonstrate the superior templating roles played by the halide ion(s). Further credence for the halide template effects was provided by the isolation of the cationic pentadecanuclear complex 3 as the sole product when tyrosine-supported hydrolysis of Gd(NO(3))(3) was carried out in the presence of competitive Cl(-). Magnetic moments of complexes 1-7 measured at room temperature by using Evans' method are in excellent agreement with those calculated by the Van Vleck equation, assuming magnetically noninteractive lanthanide ions.

Bromides↗

PubMed2001

A triboluminescent europium(III) complex.

The crystal structure of (4,4'-dimethyl-2,2'-bipyridyl)tris[3,3,3-trifluoro-1-(2-thenoyl)propan-2-onato]europium(III), or more commonly (4,4'-dimethyl-2,2'-bipyridyl)tris(2-thenoyltrifluoroacetonato)europium(III), [Eu(C8H4F3O2S)3(C12H12N2)], has been determined. Crystals of the complex emit vivid red light when scratched or fractured. This triboluminescent activity seems to correlate with the non-centrosymmetric crystal structure and disorder of the thienyl rings and CF3 groups which is present here and in similar compounds. While modeling the thienyl-ring disorder, it was noted that the bond angle at the C atom replaced by S is a sensitive sign of even small rotational ring disorder. The coordination geometry of the Eu(III) ion can be described as square antiprismatic, with coordination by the six O atoms of the three chelating beta-diketonate ligands and the two N atoms of the neutral bipyridyl ligand.

Journal Article↗

PubMed2001

Dendron-Controlled Nucleation and Growth of Gold Nanoparticles We thank the University of Arizona and the Research Corporation for financial support. Acknowledgement is also made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. The X-ray diffractometer was purchased with support from the U.S. National Science Foundation (CHEM-9610374). We thank Dr. K. Nebesny for help with the XPS experiments.

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Journal Article↗

PubMed1999

Synthesis and Structures of Solvated Monoclusters and Bridged Di- and Triclusters Based on the Cubic Building Block [Re(6)(&mgr;(3)-Se)(8)](2+).

The cluster formulated as [Re(6)Se(7)(SeH)I(6)](3)(-) has been previously shown to undergo ligand substitution reactions to generate the family [Re(6)Se(8)(PEt(3))(n)()I(6)(-)(n)()](()(n)()(-)(4)+) (n = 3-6), several members of which form solvate clusters upon treatment with Ag(I) in acetonitrile. Here it is demonstrated that additional de-iodination reactions afford solvate clusters useful in building up bridged cluster arrays. In dichloromethane/solv (5:1 v/v) in the presence of 2 equiv of AgSbF(6) at room temperature, trans-[Re(6)Se(8)(PEt(3))(4)I(2)] forms trans-[Re(6)Se(8)(PEt(3))(4)(solv)(2)](2+) (solv = MeCN (5), DMF (6), Me(2)SO (7)). The hexaiodo cluster with 6 equiv of AgSbF(6) gives the fully solvated clusters [Re(6)Se(8)(solv)(6)](2+) (solv = DMF (9), Me(2)SO (10), py (11)). In refluxing chlorobenzene for 3 days, [Re(6)Se(8)(PEt(3))(5)(MeCN)](2+) (1) and 4,4'-bipyridine (4,4'-bpy) yield [Re(6)Se(8)(PEt(3))(5)(4,4'-bpy)](2+) (12); similarly, cis- and trans-[Re(6)Se(8)(PEt(3))(4)(MeCN)(2)](2+) afford the cis- and trans-14 isomers, respectively, of [Re(6)Se(8)(PEt(3))(4)(4,4'-bpy)(2)](2+). Clusters 1 and 12 (or 1 and 1/2 equiv of 4,4-bpy) under the same conditions afford the bridged dicluster {[Re(6)Se(8)(PEt(3))(5)](2)(4,4'-bpy)}(4+) (15). The related diclusters {[Re(6)Se(8)(PEt(3))(5)](2)(L-L)}(4+) (L-L = 4,4'-py(2)C(2)H(2) (16), 4,4'-py(2)C(2)H(4) (17) (4,4'-py(2)C(2)H(2) = trans-1,2-bis(4-pyridyl)ethylene, 4,4'-py(2)C(2)H(4) = trans-1,2-bis(4-pyridyl)ethane)) are obtained by analogous methods. Reaction of 14 and 2 equiv of 1 in refluxing dichloromethane produces the linear tricluster {[Re(18)Se(24)(PEt(3))(14)(4,4'-bpy)(2)}(6+). All clusters were isolated as SbF(6)(-) salts in yields of ca. 60-90% and were characterized by their (1)H and (31)P NMR spectra and by mass spectrometry. In addition, the structures of 10 clusters (5-7, 9-12, 14-16) were confirmed by X-ray structure determinations. All clusters are based on the cubic [Re(6)(&mgr;(3)-Se)(8)](2+) core whose dimensions are insensitive to the nature and substitution pattern of the ligands. All substitution reactions, as indicated, proceed with retention of stereochemistry. Appropriate choice of solvate cluster leads to the unambiguous formation of 14-17, and should allow the construction of these and other cluster array shapes with variable bridging ligands. On the basis of voltammetric and EPR properties, clusters originally described as the monoprotonated species [Re(6)Se(7)(SeH)I(6)](3)(-) and [Re(6)S(7)(SH)Br(6)](3)(-) are reformulated as the oxidized 23-electron clusters [Re(6)Se(8)I(6)](3)(-) and [Re(6)S(8)Br(6)](3)(-).

Journal Article↗

PubMed1996

Hydrocarbon-Soluble Mercuracarborands: Syntheses, Halide Complexes, and Supramolecular Chemistry.

The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) Å, b = 18.19(1) Å, c = 13.61(1) Å, beta = 113.74(2) degrees, V = 6568 Å(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) Å, b = 21.12(2) Å, c = 20.96(2) Å, beta = 97.87(2) degrees, V = 5600 Å(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) Å, c = 21.666(2) Å, V = 10098 Å(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) Å, b = 13.013(1) Å, c = 15.867(2) Å, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 Å(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution.

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