Study of electron spin crossover in iron(III) tris-dithiocarbamate complexes by carbon-13 NMR spectroscopy

¹³C and ¹H isotropic shifts have been measured for a series of Fe(III) tris-dithiocarbamate complexes. The ¹³C isotropic shifts may be interpreted as arising solely from contact hyperfine coupling and demonstrate that as the low-spin state of the metal is favoured there is an increase in metal-ligand π-bonding. σ-delocalization of unpaired spin density is more important in determining the ¹³C isotropic shifts than those of the contiguous proton.     

Carbon-13 NMR studies of some paramagnetic transition-metal acetylacetonates some linewidth considerations

Carbon 13 isotropic shifts and linewidths have been measured for a series of paramagnetic transition-metal acetylacetonates. The results have been compared with the corresponding NMR parameters of the contiguous protons. The relaxation pathway of the ¹³C spins is controlled by hyperfine interactions with the unpaired electron spins and, in cases where the proton linewidth is also dominated by the hyperfine mechanism, good agreement is obtained between the experimental ¹³C/¹H linewidth ratio and that calculated on the basis of the contact shifts. Pseudocontact interactions can be important in determining the total isotropic shift for both the ¹³C and ¹H nuclei and contrary to previous studies, it is suggested that such effects are also important for V(III) and Mn(III) acetylacetonate.     

Chains of fused rings in the hydrogen‐bonded structure of meso‐­6,13‐di­amino‐6,13‐di­methyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane–2,2′‐biphenol (1/2)

The title compound is a salt, [C₁₂H₃₂N₆]²⁺·2[HOC₆H₄C₆H₄O]^?. The centrosymmetric cation contains two intramolecular N—H?N hydrogen bonds with an N?N distance of 2.8290 (13) Å, and the pendent amino groups are in axial sites; the anion contains an intramolecular O—H?O hydrogen bond with an O?O distance of 2.4656 (11) Å. The ions are linked into continuous chains by means of four types of N—H?O hydrogen bonds with N?O distances ranging from 2.7238 (12) Å to 3.3091 (13) Å, associated with N—H?O angles in the range 148–160°.     

Forcing Function Effects on Nonlinear Trajectories: Identifying Very Local Brain Dynamics

Effects of imposing a sinusoidal acoustic and visual forcing function at various frequencies onto an EEG process are examined in terms of various indices of the nonlinear dynamics. Conjoint use of four methods of data analysis; Lyapunov exponents, the entropic analogue of the Schwarzian derivative, surrogate distributions, and higher-order kernel analyses in the time domain, is illustrated. Local epochs with unstable dynamics are identifed on very short series.     

Narrow Parameter Windows and Analogues of Contextual Noise in Nonlinear Psychophysics

The dependency of outputs of three types; real, imaginary and cross-entropy mappings, all over a lattice of pixels, each of which is generated by a complex cubic polynomial nonlinear trajectory, is examined as a function of the cross-coupling between any pixel and its neighbourhood. It is found that the system can transmit information efficiently only within a narrow parameter window, which represents an optimum level of diffusion in space and reconfiguration in time. The topology of stimulus patterns, which are open or closed in their contours, can have a critical effect on the distribution of information in the system's output. Signals which are not processed within a limited temporal and parameter window are eventually degenerated and lost. There are phenomena associated with edge-of-chaos at some stages in the system. Problems of predictability when second-order stochastic noise is superimposed on the trajectory's parameters are explored, and differences from signal detection models are noted.