Synthesis, Crystal Structure, and Magnetic Properties of the Highly Frustrated Orthorhombic Li4MgReO6.

In an effort to understand the structure-property relationship in magnetically frustrated systems, an orthorhombic analog of the S = 1/2 Re-based oxide Li4MgReO6 has been successfully synthesized and its physical properties were investigated. Li4MgReO6 had been previously synthesized in a monoclinic system in an ordered NaCl structure type. That system was shown to exhibit spin glass behavior below ∼12 K. The crystal structure of the latter phase was determined using powder X-ray diffraction data. A structural model was refined in the orthorhombic Fddd space group that resulted in cell dimensions of a = 5.84337 (7) Å, b = 8.33995 (9) Å, and c = 17.6237 (2) Å. The magnetic ions, Re6+ (S = 1/2), consist of various arrangements of interconnected triangles and trigonal prisms that offer potential for geometric magnetic frustration. Temperature dependent magnetic susceptibility reveals an AFM transition below ∼2 K along with a ZFC/FC divergence suggestive of spin freezing. The Curie-Weiss fitting parameters to the paramagnetic regime result in θ = -124 (1) K, which is indicative of predominant AFM interactions. A frustration index of ∼62 is in accordance with a highly frustrated magnetic ground state. Zero field (ZF) µSR data provides evidence for the onset of magnetic order below 4 K, along with the evidence for dynamical fluctuations up to 5 K. Moreover, longitudinal field (LF) µSR data reveals a complete decoupling in applied field at 2 K, which is indicative of static order in most or all of the volume fraction at ∼2 K, with partial ordered volumes coexisting with dynamical fluctuations up to 5 K. Estimates of the relative strengths of various magnetic exchange pathways at the level of spin-dimer analysis for this novel system are calculated and are compared to those of the previously reported values for the monoclinic analog.

Mechanistic Insights into the Formation of Dodecanethiolate-Stabilized Magnetic Iridium Nanoparticles: Thiosulfate vs Thiol Ligands.

The synthesis of stable and isolable iridium nanoparticles with an average core size of ∼1.2 ± 0.3 nm was achieved by employing sodium S-dodecylthiosulfate as a ligand precursor during the modified Brust-Schiffrin reaction. Transmission electron microscopy (TEM) of the isolated Ir nanoparticles revealed a high degree of monodispersity. Further characterizations with 1H NMR, FT-IR, UV-vis spectroscopy, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) confirmed that the synthesized Ir nanoparticles are stabilized by dodecanethiolate ligands produced upon the adsorption/cleavage of S-dodecylthiosulfate on the growing Ir nanoparticle surface. By comparison, synthetic attempts employing dodecanethiol as a stabilizing ligand led to the formation of Ir-thiolate species (Ir(SR)3) as an intermediate and Ir-hydroxide species at the completion of reaction. Mechanistic investigations of these two reactions using S-dodecylthiosulfate and dodecanethiol provided deeper understandings on the novelty of thiosulfate ligands, which allow the successful formation of stable thiolate-capped Ir nanoparticles. Moreover, these Ir nanoparticles were shown to have strong magnetic properties.

Magnetism in dopant-free ZnO nanoplates.

It is known that bulk ZnO is a nonmagnetic material. However, the electronic band structure of ZnO is severely distorted when the ZnO is in the shape of a very thin plate with its dimension along the c-axis reduced to a few nanometers while keeping the bulk scale sizes in the other two dimensions. We found that the chemically synthesized ZnO nanoplates exhibit magnetism even at room temperature. First-principles calculations show a growing asymmetry in the spin distribution within the distorted bands formed from Zn (3d) and O (2p) orbitals with the reduction of thickness of the ZnO nanoplates, which is suggested to be responsible for the observed magnetism. In contrast, reducing the dimension along the a- or b-axes of a ZnO crystal does not yield any magnetism for ZnO nanowires that grow along c-axis, suggesting that the internal electric field produced by the large {0001} polar surfaces of the nanoplates may be responsible for the distorted electronic band structures of thin ZnO nanoplates.

Structures and magnetic behavior of 1-, 2-, and 3D coordination polymers in the Cu(II)-dicyanamide-pyrimidine family.

Using aqueous conditions, three new coordination polymers containing Cu(2+) cations, dicyanamide (dca) anions, and pyrimidine (pym) were isolated and structurally and magnetically characterized. Comprising the bulk of the product yield, Cu(dca)(2)(pym)(2), 1, crystallizes in the monoclinic space group P2(1)/c with a = 7.3569(5) A, b = 13.4482(9) A, c = 7.4559(5) A, beta = 98.984(3) degrees, and V = 728.6(1) A and forms linear 1D chains. The second compound, Cu(dca)(NO(3))(pym)(H(2)O), 2, is also monoclinic, P2(1)/n, with a = 7.6475(3) A, b = 12.2422(5) A, c = 11.0286(4) A, beta = 106.585(2) degrees, and V = 989.6(1) A(3). A 2D network structure consisting of both bridging mu-dca and pym ligands is formed while the NO(3)(-) and H(2)O are axially bonded to the Cu center. Cu(3)(dca)(6)(pym)(2).0.75H(2)O, 3, is triclinic, Ponemacr;, with a = 7.7439(4) A, b = 9.3388(5) A, c = 10.1779(5) A, alpha = 86.014(2) degrees, beta = 88.505(2) degrees, gamma = 73.623(2) degrees, and V = 704.46(9) A(3). The structure of 3 is quite unique in that [Cu(3)(pym)(2)](6+) trimers are interconnected via mu-dca ligands affording a complex 3D self-penetrating framework. Magnetically, 1 exhibits extremely weak exchange interactions along the Cu-(dca)(2)-Cu ribbons while 2 and 3 display very strong magnetic couplings mediated by the mu-bonded pym ligands. Moreover, 2 shows a broad maximum in chi(T) at 40 K and behaves as a uniform 1D antiferromagnetic chain with g = 2.09(1), J/k(B) = -42.6(1) K, and TIP = -66 x 10(-)(6) emu/mol. An S = (1)/(2) trimer model that includes intertrimer interactions successfully described the magnetic behavior of 3, yielding g = 2.10(1), J/k(B) = -69.4(5) K, theta = -0.28(3) K, and TIP = -180 x 10(-)(6) emu/mol. It is found that mu-bonded dca and pym ligands mediate very weak and very strong exchange interactions, respectively, between Cu(2+) centers.