Search results for "Field theory"
showing 10 items of 1188 documents
Gravity waves from non-minimal quadratic inflation
2015
We discuss non-minimal quadratic inflation in supersymmetric (SUSY) and non-SUSY models which entails a linear coupling of the inflaton to gravity. Imposing a lower bound on the parameter cR, involved in the coupling between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity up to the Planck scale. Working in the non-SUSY context we also consider radiative corrections to the inflationary potential due to a possible coupling of the inflaton to bosons or fermions. We find ranges of the parameters, depending mildly on the renormalization scale, with adju…
A rare isostructural series of 3d–4f cyanido-bridged heterometallic squares obtained by assembling [FeIII{HB(pz)3}(CN)3]− and LnIII ions: synthesis, …
2021
A new series of cyanido-bridged {FeIIILnIII}2 neutral molecular squares of general formula [Fe{HB(pz)3}(CN)(μ-CN)2Ln(NO3)2(pyim)(Ph3PO)]2·2CH3CN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz)3}− = hydrotris(pyrazolyl)borate, pyim = 2-(1H-imidazol-2-yl)pyridine and Ph3PO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz)3}(CN)3]− species with the preformed [LnIII(pyim)(NO3)2(pyim)(Ph3PO)]+ complex anions (generated in situ by mixing the nitrate salt of each Ln(III) ion with pyim and Ph3PO molecules). Single-crystal X-ray diffraction studies show that 1–7 are isostructural compounds that crystallize in the triclinic P space group. Their cry…
Electronic Relaxation Phenomena Following 57Co(EC)57Fe Nuclear Decay in [MnII(terpy)2](ClO4)2·1/2H2O and in the Spin Crossover Complexes [CoII(terpy)…
2001
The valence states of the nucleogenic 57Fe arising from the nuclear disintegration of radioactive 57Co by electron capture decay, 57Co(EC)57Fe, have been studied by Mossbauer emission spectroscopy (MES) in the 57Co-labeled systems: [57Co/Co(terpy)2]Cl2·5H2O (1), [57Co/Co(terpy)2](ClO4)2·1/2H2O (2), and [57Co/Mn(terpy)2](ClO4)2· 1/2H2O (3) (terpy = 2,2‘:6‘,2‘ ‘-terpyridine). The compounds 1, 2, and 3 were labeled with ca. 1 mCi of 57Co and were used as the Mossbauer sources at variable temperatures between 300 K and ca. 4 K. [Fe(terpy)2]X2 is a diamagnetic low-spin (LS) complex, independent of the nature of the anion X, while [Co(terpy)2]X2 complexes show gradual spin transition as the temp…
Spin Density Distribution in Transition Metal Complexes: Some Thoughts and Hints
1998
Abstract The spin density distribution in transition metal complexes is discussed in qualitative terms, taking into account the coexistence of spin delocalization and spin polarization mechanisms, with the help of numerical results for several complexes obtained from density functional calculations. The covalent character of the metal-ligand bonds as well as the σ- or π-characteristics of the partially filled d orbitals must be taken into account to qualitatively predict the sign of the spin density at a particular atom within a ligand. The same patterns can be applied to binuclear complexes and can be helpful in determining the ferro- or antiferromagnetic character of the exchange coupling…
Synthesis, crystal structure and magnetic properties of the Re(II) complexes NBu4[Re(NO)Br4(L)] (L = pyridine and diazine type ligands).
2013
Four novel Re(II) complexes of formula NBu4[Re(NO)Br4(L)] [NBu4(+) = tetra-n-butylammonium cation and L = pyridine (1), pyrazine (2), pyrimidine (3), pyridazine (4)] have been prepared by a substitution reaction involving NBu4[Re(NO)Br4(EtOH)] and L. Their crystal structures have been determined by single crystal X-ray diffraction. They are all mononuclear complexes whose structure is made up of [Re(NO)Br4L](-) anions and NBu4(+) cations. Each Re(II) ion is six-coordinate with four bromide ligands, a linear nitrosyl group and one monodentate nitrogen donor L building a tetragonally distorted octahedral surrounding. The Re-Br bond distances cover a narrow range [2.5048(8)-2.5333(5) Å] and th…
A heteroleptic bis(tridentate)ruthenium(II) polypyridine complex with improved photophysical properties and integrated functionalizability.
2010
The synthesis and photophysical properties of a ruthenium(II) complex bearing an electron-accepting 2,2';6',2''-terpyridine ligand and an electron-donating N,N'-dimethyl-N,N'-dipyridin-2-ylpyridine-2,6-diamine (ddpd) ligand are presented. The heteroleptic complex is easily prepared isomerically pure and features intense low-energy metal-to-ligand charge-transfer (MLCT) absorption bands and intense room temperature (3)MLCT emission with a long (3)MLCT lifetime. The favorable photophysical properties are due to the strong ligand field imposed by the ddpd ligand.
The crystal structure and magnetic properties of 3-pyridinecarboxylate-bridged Re(ii)M(ii) complexes (M = Cu, Ni, Co and Mn)
2015
The novel Re(II) complex NBu4[Re(NO)Br4(Hnic)] (1) and the heterodinuclear compounds [Re(NO)Br4(μ-nic)Ni(dmphen)2]·½CH3CN (2), [Re(NO)Br4(μ-nic)Co(dmphen)2]·½MeOH (3), [Re(NO)Br4(μ-nic)Mn(dmphen)(H2O)2]·dmphen (4), [Re(NO)Br4(μ-nic)Cu(bipy)2] (5) [Re(NO)Br4(μ-nic)Cu(dmphen)2] (5') (NBu4(+) = tetra-n-butylammonium cation, Hnic = 3-pyridinecarboxylic acid, dmphen = 2,9-dimethyl-1,10-phenanthroline, bipy = 2,2'-bipyridine) have been prepared and the structures of 1-5 determined using single crystal X-ray diffraction. The structure of 1 consists of [Re(NO)Br4(Hnic)](-) anions and NBu4(+) cations. Each Re(II) is six-coordinate with four bromide ligands, a linear nitrosyl group and a nitrogen ato…
Two-Level Self-Organisation of Arrays of [2×2] Grid-Type Tetranuclear Metal Complexes by Hydrogen Bonding
2001
Here we report on the synthesis and characterisation of four new complexes of the [2×2] M4II grid-type (M = Co, Fe, Zn) with oligopyridine-derived ligands. The presence of aminopyrazine and aminopyrimidine moieties at the edge of the ligands potentially enables the formation of infinite hydrogen-bonded multi-grid networks. The ligands were synthesised by subsequent stannylations and Stille-type coupling reactions. The complexes were obtained by self-assembly of the ligand with the metal salt. The single-crystal X-ray structure was determined for the Co complex 7 containing aminopyrimidine as the hydrogen-bonding moiety [P1¯; a = 15.4976(4), b = 18.2114(6), c = 31.9538(10) A, α = 86.9809(13)…
A new lattice action for studying topological charge
1996
We propose a new lattice action for non-abelian gauge theories, which will reduce short-range lattice artifacts in the computation of the topological susceptibility. The standard Wilson action is replaced by the Wilson action of a gauge covariant interpolation of the original fields to a finer lattice. If the latter is fine enough, the action of all configurations with non-zero topological charge will satisfy the continuum bound. As a simpler example we consider the $O(3)$ $\sigma$-model in two dimensions, where a numerical analysis of discretized continuum instantons indicates that a finer lattice with half the lattice spacing of the original is enough to satisfy the continuum bound.
Three-dimensional singletons
1990
The three-dimensional analog of singleton gauge theory turns out to be related to the topological gauge theory of Schwartz and Witten. It is a fully-fledged gauge theory, though it involves only a single scalar field. Real, physical degrees of freedom propagate in 3-space, but they are ‘confined’ in the sense that they cannot be detected locally. The physical Hamiltonian density is not zero, but it is concentrated on the boundary at spatial infinity. This boundary surface, a torus, supports a two-dimensional conformal field theory.