Hongxue Liu

Water-Dispersible Iron Oxide Magnetic Nanoparticles with Versatile Surface Functionalities

We report a simple one-pot strategy to prepare surface-function-alized, water-dispersible iron oxide nanoparticles. Small organic molecules that have desired functional groups such as amines, carboxylics, and thiols are chosen as capping agents and are injected into the reaction medium at the end of the synthesis. A diversity of functionalities are effectively introduced onto the surface of the nanoparticles with a minimal consumption of solvents and chemical resources by simply switching the capping ligand to form the ligand shell. The resulting nanocrystals are quasi-spherical and narrowly size-distributed. Energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy studies suggest a successful surface modification of iron oxide nanoparticles with selected functionalities. The colloidal stabilities are characterized by dynamic light scattering and zeta potential measurements. The results imply that functionalized nanoparticles are very stable and mostly present as individual units in buffer solutions. The pedant functional groups of the capping ligand molecules are very reactive, and their availabilities are investigated by covalently linking fluorescent dyes to the nanoparticles through the cross-linking of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The quenched quantum yield and shortened lifetime of the dyes strongly indicate a direct bonding between the functional group of the nanoparticles and the fluorescent molecules.

Solid-state coordination chemistry of copper(II) tetrazolates: anion control of frameworks constructed from trinuclear copper(II) building blocks.

The products of the reactions of copper(II) starting materials with 4-pyridyltetrazole (4-Hpt) in N,N-dimethylformamide (DMF)/methanol solutions are determined by the anion identity and concentration. In the absence of chloride, the 3-D open-framework material [Cu(3)(OH)(3)(4-pt)(3)(DMF)(4)].5DMF.3MeOH (1.5DMF.3MeOH) is isolated, while variations in the chloride concentration yield the 2-D and 3-D materials, 2 and 3, respectively. All three structures exhibit trinuclear copper(II) building blocks: the triangular {Cu(3)(mu(3)-OH)}(5+) core in 1 and {Cu(3)Cl(4)(4-pt)(4)(4-Hpt)(2)}(2-) and {Cu(3)Cl(2)(4-pt)(8)}(4-) chains in 2 and 3, respectively. All three materials display microporosity, which is highly dependent on the method of sample preparation.

Construction of metal-organic oxides from molybdophosphonate clusters and copper-bipyrimidine building blocks.

A series of organic-inorganic hybrid materials of the copper(II)-molybdophosphonate family have been prepared using conventional hydrothermal conditions. The reactions of MoO(3), copper(II) acetate, bipyrimidine (bpyr), a phosphonic acid, and water at temperatures below 160 degrees C and in the presence of a mineralizer such as acetic acid or HF provided crystalline samples of materials of the general class {Cu(2)(bpyr)}(4+)/Mo(x)O(y)-phosphonate. The recurrent themes of the structures are the presence of the binuclear {Cu(2)(bpyr)}(4+) and pentanuclear {Mo(5)O(15)(O(3)PR)(2)}(4-) building blocks. For the alkylphosphonate-containing materials, [{Cu(2)(bpyr)(2)}Mo(5)O(15)(O(3)PCH(3))(2)].2.5H(2)O (1.2.5H(2)O) is two-dimensional and exhibits {Cu(bpyr)}(n)(2n+) chains, while [{Cu(2)(bpyr)(H(2)O)}Mo(5)O(15)(O(3)PCH(2)CH(3))(2)] (2) is three-dimensional. The diphosphonate series of materials {{Cu(2)(bpyr)}(4+)[Mo(5)O(15){O(3)P(CH(2))(n)PO(3)}](4-) with n = 2-6 (4, 5, 7-9) in all cases contain the characteristic [Mo(5)O(15){O(3)P(CH(2))(n)PO(3)}](n)(2n+) chains, linked through {Cu(2)(bpyr)}(4+) rods into three-dimensional frameworks. When n = 1, the three-dimensional phase [{Cu(2)(bpyr)}MoO(2)(HO(3)PCH(2)PO(3))(2)].2H(2)O (3.2H(2)O) is obtained, the exclusive example of a structure constructed from isolated {MoO(6)} polyhedra rather than pentamolybdate clusters. The Ni(II)-containing phase [{Ni(2)(bpyr)(H(2)O)(4)}Mo(5)O(15){O(3)P(CH(2))(3)PO(3)}].9H(2)O (6.9H(2)O) was also prepared and compared to the structure of the Cu(II) analogue, [{Cu(2)(bpyr)(H(2)O)(4)}Mo(5)O(15){O(3)P(CH(2))(3)PO(3)}].3H(2)O (5.3H(2)O). Magnetic susceptibility studies of the compounds revealed that the magnetic behavior was consistent in all cases with antiferromagnetically coupled dimers. However, the magnitude of the exchange coupling was clearly dependent on the orientation of the M(II) mean equatorial or basal planes relative to the bipyrimidine plane. Thus, when the metal and bipyrimidine planes are nearly coplanar, the J values are in the -77 to -87 cm(-1) range, while J values of -2 to -5 cm(-1) are observed for the compounds with out-of-plane orientations.

Hydrothermal chemistry of vanadium oxides with aromatic di- and tri-phosphonates in the presence of secondary metal copper(II) cationic complex subunits

The hydrothermal chemistry of the copper-organonitrogen ligand/vanadium oxide/aromatic phosphonate system has been studied. Not only was HF required to induce crystallization, but product composition was highly dependent on the HF/V ratio of the reactions. At relatively low concentrations of HF/V of 6:1, materials of the Cu(II)-ligand/VxOy/organophosphonate type were observed, namely, [{Cu(phen)}2V2O5(O3PC6H4PO3)] (1), [Cu(phen)VO2(HO3PC6H4PO3)] (2), [{Cu(terpy)}2V2O5(O3PC6H4PO3)] (3), [{Cu(phen)(H2O)}VO2(HO3PC6H4PO3)] (6), [{Cu(phen)}VO2(HO3PC6H4PO3)] (7a and 7b), [Cu(C5H4NCO2)2V2O4(HO3PC6H4POH3)] (8), [Cu(bpy)VO2 {(HO3P)3C6H3}]·1.5H2O (12·1.5H2O), [{Cu(bpy)}2V3O7{(O3P)2C6H3PO3H}] (13) and [Cu(phen)V3O6(H2O){(O3P)2C6H3(PO3H)}] (14). When the HF concentration was raised, materials incorporating fluoride anion were observed; that is, compounds of the Cu(II)-ligand/VxOyFz/organophosphonate type: [{Cu(bpa)}2VO2F(H2O)(O3PC6H4PO3)]·H2O (4), [{Cu(bpa)}2V2O4F2(O3PC6H4PO3)] (5), [{Cu(bpy)}2V2O4F2(O3PC6H4PO3)] (9), [{Cu(terpy)}2V3O6F(HO3PC6H4PO3)2] (10), [{Cu(bpa)}2V2O4F2(O3PC6H4PO3)] (11). At HF/V concentrations of 25:1 or greater, vanadium free products, Cu(II) ligand/organophosphonate, were obtained: [Cu(C5H4NCO2)2(H2O3PC6H4PO3H2)]·H2O (15·H2O), [Cu(C5H4NCO2)2(H2O3PC6H4PO3H2)] (16), [Cu(bpy)(H2O){(HO3P)2C6H3(PO3H2)}] (17), [Cu(bpy){(HO3P)2C6H3(PO3H2)}]·H2O (18·H2O), [Cu(phen){(H2O3P)C6H3(PO3H)2}]·2H2O (19·2H2O) and [Cu(bpa){H2O3PC6H3(PO3H)2}]·H2O (20·H2O). The structural chemistry is unusually diverse with the Cu(II) ligand/VxOy/organophosphonate series exhibiting one-, two- and three-dimensional structures with a variety of copper-vanadate and vanadophosphonate substructures. The structural chemistry is discussed in relation to other examples of materials of the Cu(II) ligand/VxOy/organophosphonate and Cu(II) ligand/VxOyFz/organophosphonate families.

Intrinsic magnetism in BaTiO3 with magnetic transition element dopants (Co, Cr, Fe) synthesized by sol-precipitation method

A study of BaTiO3 nanoparticles doped with different transition metals including Co, Fe, and Cr is presented. X-ray diffraction and electron microscopy studies indicated that all the samples are highly crystalline and that transition metal dopants are successfully incorporated into BaTiO3 without detectable secondary phases. Raman spectra featured three characteristic broad bands centered approximately 300, 520, and 715 cm−1 from the tetragonal BaTiO3 without any extra peak present that may be attributed to other impurity phases. Temperature- and field-dependent magnetometry measurements and analysis revealed that all the samples show paramagnetic-like behavior originating from the transition metal ions. These results not only allow the exclusion of potential secondary ferromagnetic or antiferromagnetic phases, but also suggest that transition metal ions (Co, Cr, and Fe) in BaTiO3 shown in this study are present as isolated paramagnetic centers.