Study of Optical and Magnetic Properties of Graphene-Wrapped ZnO Nanoparticle Hybrids

In this work, we report a one-step method for the preparation of graphene-wrapped zinc oxide (ZnO) nanoparticle (NP) (ZnO@G) hybrids. These hybrids are characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, optical absorption measurements, photoluminescence (PL) emission spectroscopy, and <i>M</i>–<i>H</i> hysteresis measurements. All results reveal that the ZnO NPs are entirely covered with graphene sheets. In the PL spectra, the quenching of the band gap emission and the enhanced green emission serve as evidence of the electron transfer from the ZnO NPs to the graphene layer. The increase of the room-temperature magnetization of the hybrid, compared to pure ZnO NPs, is due to the increasing defect concentration. We suggest a band diagram model that accounts for these observations. We present the simple wet-chemical synthesis procedure to open a new way for the synthesis of NP–graphene hybrid systems having magnetic properties giving the large manifold potential application

Structures, Magnetochemistry, Spectroscopy, Theoretical Study, and Catechol Oxidase Activity of Dinuclear and Dimer-of-Dinuclear Mixed-Valence Mn^IIIMn^II Complexes Derived from a Macrocyclic Ligand

The work in this paper presents syntheses, characterization, magnetic properties (experimental and density functional theoretical), catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) studies of two mixed-valence dinuclear Mn^IIIMn^II complexes, [Mn^IIIMn^IIL­(μ-O₂CMe)­(H₂O)₂]­(ClO₄)₂·H₂O·MeCN (<b>1</b>) and [Mn^IIIMn^IIL­(μ-O₂CPh)­(MeOH)­(ClO₄)]­(ClO₄) (<b>2</b>), and a Mn^IIIMn^IIMn^IIMn^III complex, [{Mn^IIIMn^IIL­(μ-O₂CEt)­(EtOH)}₂(μ-O₂CEt)]­(ClO₄)₃ (<b>3</b>), derived from the Robson-type macrocycle H₂L, which is the [2 + 2] condensation product of 2,6-diformyl-4-methylphenol and 2,2-dimethyl-1,3-diaminopropane. In <b>1</b> and <b>2</b> and in two Mn^IIIMn^II units in <b>3</b>, the two metal centers are bridged by a bis­(μ-phenoxo)-μ-carboxylate moiety. The two Mn^II centers of the two Mn^IIIMn^II units in <b>3</b> are bridged by a propionate moiety, and therefore this compound is a dimer of two dinuclear units. The coordination geometry of the Mn^III and Mn^II centers are Jahn–Teller distorted octahedral and distorted trigonal prism, respectively. Magnetic studies reveal weak ferro- or antiferromagnetic interactions between the Mn^III and Mn^II centers in <b>1</b> (<i>J</i> = +0.08 cm^–1), <b>2</b> (<i>J</i> = −0.095 cm^–1), and <b>3</b> (<i>J</i>₁ = +0.015 cm^–1). A weak antiferromagnetic interaction (<i>J</i>₂ = −0.20 cm^–1) also exists between the Mn^II centers in <b>3</b>. DFT methods properly reproduce the nature of the exchange interactions present in such systems. A magneto-structural correlation based on Mn–O bridging distances has been proposed to explain the different sign of the exchange coupling constants. Utilizing 3,5-di-<i>tert</i>-butyl catechol (3,5-DTBCH₂) as the substrate, catecholase activity of all the three complexes has been checked in MeCN and MeOH, revealing that all three are active catalysts with <i>K</i>_cat values lying in the range 7.5–64.7 h^–1. Electrospray ionization mass (ESI-MS positive) spectra of the complexes <b>1</b>–<b>3</b> have been recorded in MeCN solutions, and the positive ions have been well characterized. ESI-MS positive spectrum of complex <b>1</b> in presence of 3,5-DTBCH₂ has also been recorded, and a positive ion, [Mn^IIIMn^IIL­(μ-3,5-DTBC^2–)]⁺, having most probably a bridging catecholate moiety has been identified

A Series of M^IICu^II₃ Stars (M = Mn, Ni, Cu, Zn) Exhibiting Unusual Magnetic Properties

The work in this report describes the syntheses, electrospray ionization mass spectromtery, structures, and experimental and density functional theoretical (DFT) magnetic properties of four tetrametallic stars of composition [M^II(Cu^IIL)₃]­(ClO₄)₂ (<b>1</b>, M = Mn; <b>2</b>, M = Ni; <b>3</b>, M = Cu; <b>4</b>, M = Zn) derived from a single-compartment Schiff base ligand, <i>N</i>,<i>N</i>′-bis­(salicylidene)-1,4-butanediamine (H₂L), which is the [2 + 1] condensation product of salicylaldehyde and 1,4-diaminobutane. The central metal ion (Mn^II, Ni^II, Cu^II, or Zn^II) is linked with two μ₂-phenoxo bridges of each of the three [Cu^IIL] moieties, and thus the central metal ion is encapsulated in between three [Cu^IIL] units. The title compounds are rare or sole examples of stars having these metal-ion combinations. In the cases of <b>1</b>, <b>3</b>, and <b>4</b>, the four metal ions form a centered isosceles triangle, while the four metal ions in <b>2</b> form a centered equilateral triangle. Both the variable-temperature magnetic susceptibility and variable-field magnetization (at 2–10 K) of <b>1</b>–<b>3</b> have been measured and simulated contemporaneously. While the Mn^IICu^II₃ compound <b>1</b> exhibits ferromagnetic interaction with <i>J</i> = 1.02 cm^–1, the Ni^IICu^II₃ compound <b>2</b> and Cu^IICu^II₃ compound <b>3</b> exhibit antiferromagnetic interaction with <i>J</i> = −3.53 and −35.5 cm^–1, respectively. Variable-temperature magnetic susceptibility data of the Zn^IICu^II₃ compound <b>4</b> indicate very weak antiferromagnetic interaction of −1.4 cm^–1, as expected. On the basis of known correlations, the magnetic properties of <b>1</b>–<b>3</b> are unusual; it seems that ferromagnetic interaction in <b>1</b> and weak/moderate antiferromagnetic interaction in <b>2</b> and <b>3</b> are possibly related to the distorted coordination environment of the peripheral copper­(II) centers (intermediate between square-planar and tetrahedral). DFT calculations have been done to elucidate the magnetic properties. The DFT-computed <i>J</i> values are quantitatively (for <b>1</b>) or qualitatively (for <b>2</b> and <b>3</b>) matched well with the experimental values. Spin densities and magnetic orbitals (natural bond orbitals) correspond well with the trend of observed/computed magnetic exchange interactions