Formation of Ni[C4(CN)8] from the reaction of Ni(COD)2 (COD = 1,5-cyclooctadiene) with TCNE in THF

Journal ArticleThe dissolution of Ni(COD)2 (COD = 1,5-cyclooctadiene) into dichloromethane leads to decomposition and formation of a room temperature magnetic material, whereas the reaction of Ni(COD)2 and tetracyanoethylene (TCNE) in THF forms paramagnetic materials including NiII[C4(CN)8](THF)2.xTHF. These results are discussed in context with a recent report of a room temperature magnet based upon the reaction of Ni(COD)2 and TCNE in dichloromethane

Effect of solvent on the magnetic properties of the high-temperature V[TCNE]x molecule-based magnet

Journal ArticleThe different magnetic behaviors of the V[TCNE]x (TCNE=tetracyanoethylene) magnet prepared via the reaction of TCNE and V(CO)6 in CH2Cl2 and the solvent-free chemical vapor deposition (CVD) of TCNE and V(CO)6 onto a glass substrate were determined. It was shown that the presence of noncoordinating CH2Cl2 solvent molecules in the structure of the V[TCNE]x magnet does not substantially influence the magnetic ordering temperature; however, it creates additional structural disorder. This results in a correlated spin-glass behavior in low magnetic fields (H<100 Oe) at helium temperatures, small remanence, and vanishing coercive fields at room temperature. In contrast, the CVD-prepared film has increased structural order. Quantitatively, the degree of disorder was analyzed in the framework of the random magnetic anisotropy model

Dielectric properties of BaMg1∕3Nb2∕3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

Ba(Mg1∕3Nb2∕3)O3 (BMN) doped and undoped Ba0.45Sr0.55TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss (∼38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg2+ whose detrimental effect on tunability is partially compensated by small Nb5+ as the two substitute Ti4+ in the BST. The coupling between MgTi″ and VO•• charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300–450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from MgTi″, VO•• and NbTi• charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole–Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled NbTi• sitting as a positive trap center at the shallow donor level of the BST

Toward the Mechanism of Perchlorinated Cyclopentasilane (Si₅Cl₁₀) Ring Flattening in the [Si₅Cl₁₀·2Cl]^2– Dianion

We report the detailed computational study of flattening of the puckered Si₅ ring by suppression of the pseudo-Jahn–Teller (PJT) effect through coordination of two Cl^– anions to the molecule forming an inverse sandwich dianion [Si₅Cl₁₀·2Cl]^2– complex. The PJT effect that causes nonplanarity of the Si₅Cl₁₀ structure (<i>C</i>_<i>s</i>) results from vibronic coupling of pairs of occupied molecular orbitals (OMOs) and unoccupied molecular orbitals (UMOs). It was shown that filling the intervenient molecular orbitals of puckered Si₅Cl₁₀ with valent electron pairs of Cl^– donors suppresses the PJT effect, with the Si₅ ring becoming planar (<i>D</i>_5<i>h</i>) upon complex formation. In this paper, the stabilization energy <i>E</i>(2) associated with donor–acceptor charge transfer (delocalization) was estimated using NBO analysis for all studied inverse sandwich compounds [Si₅Cl₁₀·2X]^2– (where X = F, Cl, Br). It was found that the polarizability of the donor ion might significantly affect the stabilization energy value and should be taken into account when choosing the ligands suitable for forming Si-based one-dimensional compounds and other nanoscale materials

Toward the Mechanism of Perchlorinated Cyclopentasilane (Si₅Cl₁₀) Ring Flattening in the [Si₅Cl₁₀·2Cl]^2– Dianion

We report the detailed computational study of flattening of the puckered Si₅ ring by suppression of the pseudo-Jahn–Teller (PJT) effect through coordination of two Cl^– anions to the molecule forming an inverse sandwich dianion [Si₅Cl₁₀·2Cl]^2– complex. The PJT effect that causes nonplanarity of the Si₅Cl₁₀ structure (<i>C</i>_<i>s</i>) results from vibronic coupling of pairs of occupied molecular orbitals (OMOs) and unoccupied molecular orbitals (UMOs). It was shown that filling the intervenient molecular orbitals of puckered Si₅Cl₁₀ with valent electron pairs of Cl^– donors suppresses the PJT effect, with the Si₅ ring becoming planar (<i>D</i>_5<i>h</i>) upon complex formation. In this paper, the stabilization energy <i>E</i>(2) associated with donor–acceptor charge transfer (delocalization) was estimated using NBO analysis for all studied inverse sandwich compounds [Si₅Cl₁₀·2X]^2– (where X = F, Cl, Br). It was found that the polarizability of the donor ion might significantly affect the stabilization energy value and should be taken into account when choosing the ligands suitable for forming Si-based one-dimensional compounds and other nanoscale materials

Mechanism of Charged, Neutral, Mono‑, and Polyatomic Donor Ligand Coordination to Perchlorinated Cyclohexasilane (Si₆Cl₁₂)

We report the detailed computational study of several perchlorinated cyclohexasilane (Si₆Cl₁₂)-based inverse sandwich compounds. It was found that regardless of the donor ligand size and charge, for example, Cl^– and CN^– anions or neutral HCN and NCPh nitriles, their coordination to the puckered Si₆Cl₁₂ ring results in its flattening. The NBO and CDA studies of the complexes showed that coordination occurs due to hybridization of low-lying antibonding σ*­(Si–Cl) and σ*­(Si–Si) unoccupied molecular orbitals (UMOs) of Si₆Cl₁₂ and occupied molecular orbitals (OMOs) of donor molecules (predominantly lone-pair-related), resulting in donor-to-ring charge transfer accompanied by complex stabilization and ring flattening. It is known that the Si₆ ring distortion results from vibronic coupling of OMO and UMO pairs (pseudo-Jahn–Teller effect, PJT). Consequently, the Si₆ ring flattening most probably occurs due to suppression of the PJT effect in all of the studied compounds. In this paper, the stabilization energy <i>E</i>(2) associated with donor–acceptor charge transfer (delocalization) was estimated using NBO analysis for [Si₆Cl₁₂·2Cl]^2–, [Si₆Cl₁₂·2­(NC)]^2–, Si₆Cl₁₂·2­(NCH), and Si₆Cl₁₂·2­(NCPh). It was found that the polarizability of the donor might significantly affect the stabilization energy value (Cl^– > CN^– > HCN). For the neutral complexes, the <i>E</i>(2) value is correlated with the charge on the nitrogen atoms. All of these factors, that is, specific donor <i>E</i>(2) value, charge transfer, complex MO energy diagrams, and so on, should be taken into account when choosing the ligands suitable for forming Si-based 1D compounds and other nanoscale materials