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Picosecond nonlinear absorption dynamics of neutral metal-dithiolenes belonging to the general class [M(R,R'timdt)[sub 2]] (M=Ni, Pd, Pt; R,R' timdt=monoreduced form of disubstituted imidazolidine-2,4,5-trithione) has been investigated at λ=1064 nm using the pump-probe technique. Both central metal ion M and substituents R,R' have been found to strongly influence the temporal evolution of the absorption saturation. In particular, it has been observed that the intersystem crossing rate always increases by a factor ∼1.5 when changing the central metal from Pd to Pt. The mechanisms leading to the measured dynamics have been explained using a multilevel rate equation analysis, based on the results of relativistic time-dependent density functional calculations. [ABSTRACT FROM AUTHOR]

Nonrelativistic and relativistic time-dependent density functional calculations are performed on the excited states of the [M(H2timdt)(sub 2)] (M = Ni, Pd, Pt) compounds. In all members of the series, the excited state at the lowest energy corresponds to a HOMO -> LUMO excitation and indicates that a large number of the transitions have an intraligand character.

The novel enantiopure dipyridyl spacer 2,2'-dimethoxy-1,1'-binaphthyl-3,3'-bis(4-pyridyl-amido) (R)-L has been designed as a robust source of axial chirality to obtain helical coordination polymers. The reaction of (R)-L and the differently substituted dithiophosphato complexes [Ni((RO)2PS2)2] [R = Me (1), Et (2)] efficiently yielded coordination polymers (1⋅L)∞ and (2⋅L)∞, respectively, consisting of helical chains in which the nickel(II) ions of the [Ni((RO)2PS2)2] units are bridged by the enantiopure L ligands. The obtained polymers differ in terms of the configuration at the metal centres, which is trans and cis for (1⋅L)∞ and (2⋅L)∞, respectively. The cis configuration in (2⋅L)∞ generates a further element of chirality around the metal center, which occurs stereospecifically, as only one enantiomeric form is present, with homochiral helices packed with opposite screw sense in the crystal. The electronic and structural features of L, (1⋅L)∞, and (2⋅L)∞ have been investigated by means of DFT theoretical calculations, and the theoretical results have been compared with the experimental ones coming from single-crystal X-ray diffraction. The cis/trans isomerism displayed by the metal centers in (1⋅L)∞ and (2⋅L)∞ has been tentatively explained on the basis of the results of theoretical calculations performed on hypothetical pentacoordinated intermediates. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to obtain an existence result for the integral equation u (t) = φ (t, u (t)) + ∫ab ψ (t, s, u (s)) ds, t ∈ [a, b] where φ : [a, b] x ℝ → ℝ and ψ : [a, b] x [a, b] x ℝ → ℝ are continuous functions which satisfy some special growth conditions. The main idea is to transform the integral equation into a fixed point problem for a condensing map T : C [a, b] → C [a, b]. The "a priori estimate method" (which is a consequence of the invariance under homotopy of the degree defined for α-condensing perturbations of the identity) is used in order to prove the existence of fixed points for T. Note that the assumptions on functions ' and do not generally assure the compactness of operator T, therefore the Leray-Schauder degree cannot be used (see K. Deimling [2, Example 9.1, p. 69]). [ABSTRACT FROM AUTHOR]