Mechanism of Charged, Neutral, Mono-, and Polyatomic Donor Ligand Coordination to Perchlorinated Cyclohexasilane (SiCl).

We report the detailed computational study of several perchlorinated cyclohexasilane (SiCl)-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 SiCl 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 SiCl 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.

Toward the Mechanism of Perchlorinated Cyclopentasilane (SiCl) Ring Flattening in the [SiCl·2Cl] Dianion.

We report the detailed computational study of flattening of the puckered Si ring by suppression of the pseudo-Jahn-Teller (PJT) effect through coordination of two Cl anions to the molecule forming an inverse sandwich dianion [SiCl·2Cl] complex. The PJT effect that causes nonplanarity of the SiCl structure (C) 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 SiCl with valent electron pairs of Cl donors suppresses the PJT effect, with the Si ring becoming planar (D) upon complex formation.

Thiophene-Fused Nickel Dithiolenes: A Synthetic Scaffold for Highly Delocalized π-Electron Systems.

A series of thiophene-fused nickel dithiolene complexes have been prepared via synthetic methods which allow the addition of peripheral aryl groups to the fused thiophene of the dithiolene ligand, thus providing access to a range of structural and electronic modifications to the dithiolene core. X-ray structural studies of the anionic complexes show that the peripheral aryl rings lie in near-perfect coplanarity to the dithiolene core and can form π-stacked columns with N-methylpyridinium cations. Density functional theory calculations show significant delocalization of the frontier orbital electron density into the peripheral aryl rings.

Carrier transport in the V[TCNE]x (TCNE = tetracyanoethylene; x ~ 2) organic-based magnet.

The carrier transport of chemical vapor deposition (CVD) prepared films of the room temperature organic-based magnet V[TCNE]x (TCNE = tetracyanoethylene; x ~ 2) over a broad temperature and magnetic field range is reported. Due to disorder the [TCNE](·-) sites are located in statistically different environments, and their energies vary from site-to-site, which leads to tailing the density of states into the energy gap, creating electronic traps and suppressing the electron mobility. Conversely, these variations have little effect on the valence band derived from the octahedral V(II)3d(t(2g)) levels, and, hence, on the hole mobility.

Chemical bonding and magnetic exchange in two-dimensional [M(TCNE)(NCMe)2]X (M = Fe, Mn; X = FeCl4, SbF6) magnets: a pressure study.

Pressure-dependent X-ray diffraction studies reveal the bulk modulus and compression anisotropy of the 2D magnet [Mn(TCNE)(NCMe)(2)]SbF(6). The Raman response of this and the similar [Fe(TCNE)(NCMe)(2)]FeCl(4) layered magnet, shows that the evolution of the a(g) ν(C=C) frequency correlates well with the magnetic exchange and T(c) variations of these materials under pressure. There is a significantly more complex correlation between the a(g) ν(C≡N) frequency and T(c) despite the fact that some unpaired π* electron density (~0.

Spectroscopic study of (two-dimensional) molecule-based magnets: [M(II)(TCNE)(NCMe)2][SbF6] (M = Fe, Mn, Ni).

The M-[TCNE] (M = 3d metal; TCNE = tetracyanoethylene) system is one of the most interesting classes of molecule-based magnets, exhibiting a plethora of compositions and structures (inorganic polymer chains, 2D layers, 3D networks, and amorphous solids) with a wide range of magnetic ordering temperatures (up to 400 K). A systematic study of vibrational (both infrared and, for the first time, Raman) properties of the family of new TCNE-based magnets of M(II)(TCNE) (NCMe)(2)[SbF(6)] [M = Mn, Fe, Ni] composition is discussed in conjunction with their magnetic behavior and newly reso-lved crystal structures. The vibrational properties of the isolated TCNE(●-) anion in the paramagnetic Bu(4)N [TCNE(●-)] salt and recently characterized 2D layered magnet Fe(II)(TCNE)(NCMe)(2)[FeCl(4)] are also reported for comparison.

Flattening a puckered cyclohexasilane ring by suppression of the pseudo-Jahn-Teller effect.

We report the experimental and theoretical characterization of neutral Si(6)X(12) (X = Cl, Br) molecules that contain D(3d) distorted six-member silicon rings due to a pseudo-Jahn-Teller (PJT) effect. Calculations show that filling the intervenient molecular orbitals with electron pairs of adduct suppresses the PJT effect in Si(6)X(12), with the Si(6) ring becoming planar (D(6h)) upon complex formation. The stabilizing role of electrostatic and covalent interactions between positively charged silicon atoms and chlorine atoms of the subject [Si(6)Cl(14)](2-) dianionic complexes is discussed.

Synthesis and magnetic properties of a [Ni(II)(TCNE)(NCMe)2-delta][BF4] magnet (Tc = 40 K).

The reaction of (NBu4)(TCNE) (TCNE = tetracyanoethylene) and [Ni(NCMe)6][BF4]2 in CH2Cl2 forms layered [Ni(TCNE)(MeCN)2-delta][BF4], a magnet ( Tc = 40 K) with a ferromagnetic interaction within Ni-mu 4-[TCNE](*-) layers, and a new general route to the preparation of [M(TCNE)(NCMe)2][anion] magnets has been identified.

Acetonitrile-facilitated reductive dimerization of TCNE to octacyanobutanediide, [C4(CN)8]2-, by Iron(II) chloride.

The redox properties of MCl2 (M=Mn, Fe, Co) acetonitrile solvates were electrochemically and spectroscopically characterized. The three voltammogram waves at 0.86, 0.

Structural and magnetic properties of MCl2 (M = Fe, Mn, Co): acetonitrile solvates.

MIICl2 (M = Mn, Fe, Co) as their acetonitrile solvates were isolated, and their structural, spectroscopic, and magnetic properties were studied. MCl2(NCMe)2 (M = Fe, Mn) form 1-D chains of octahedral MII ions with four bridging chlorides and two axial MeCN's. The presence of an axial distortion for MFe causes a significant magnetic anisotropy that increases significantly below 150 K; however, chiav [=(chi parallel + 2chi perpendicular)/3] almost coincides with the value obtained on a polycrystalline sample.

Magnetic ordering (Tc = 90 K) observed for layered [Fe(II)(TCNE*-)(NCMe)2]+[Fe(III)Cl4]- (TCNE = tetracyanoethylene).

[Fe(TCNE)(NCMe)2][FeCl4] is isolated from the reaction of TCNE and FeCl2(NCMe)2 and orders as a ferrimagnet below 90 K and is the initial member of a new class of magnets. It is the first metal-TCNE magnet with direct bonding between metal ion and [TCNE]*- whose structure has been determined, and it possesses a novel planar mu4-[TCNE]*- spin coupling unit bonded to four FeII's, with an axial pair of MeCNs. The [FeIIICl4]- anion occupies sites between the [FeII(TCNE*-)(NCMe)2]+ layers.

Cyano-bridged hexanuclear Fe4M2 (M = Ni, Co, Mn) clusters: spin-canted antiferromagnetic ordering of Fe4Ni2 cluster.

Heterobimetallic hexanuclear cyano-bridged complexes, [{Fe(Tp)(CN)3}4{M(MeCN)(H2O)2}(2)].10H2O.2MeCN [M = Ni (1), Co (2), Mn (3); Tp = hydrotris(1-pyrazolyl)borate], have been synthesized in H2O-MeCN solution.

Structural and Magnetic Properties of M(mnt)(2) Salts (M = Ni, Pt, Cu) with a Ferrocene-Based Cation, [FcCH(2)N(CH(3))(3)](+). Interplay between M.M and M.S Intermolecular Interactions.

A series of metal bis-mnt complexes (mnt = 1,2-dithiolatomaleonitrile) with the trimethylammonium methylferrocene cation have been synthesized and characterized using X-ray diffraction, magnetic susceptibility, and differential scanning calorimetry measurements. The complexes have the formulas (FcCH(2)NMe(3))[Ni(mnt)(2)] (2), (FcCH(2)NMe(3))[Pt(mnt)(2)] (3), and (FcCH(2)NMe(3))(2)[Cu(mnt)(2)] (4) (where Fc = ferrocene). At 300 K, the crystal structures of 1:1 complexes 2 and 3 are very similar.