Nanocrystals of Cs 2 SnX 6 (X = Cl, Br, Br 0.5 I 0.5 , and I) have been prepared by a simple, optimized, hot-injection method, reporting for the first time the synthesis of Cs 2 SnCl 6 , Cs 2 SnBr 6 , and mixed Cs 2 Sn(I 0.5 Br 0.5 ) 6 nanocrystalline samples. They all show a cubic crystal structure with a linear scaling of lattice parameter by changing the halide size. The prepared nanocrystals have spherical shape with average size from 3 to 6 nm depending on the nature of the halide and span an emission range from 444 nm (Cs 2 SnCl 6 ) to 790 nm (Cs 2 SnI 6 ) with a further modulation provided by mixed Br/I systems.
Push-pull terpyridine derivatives 3 were synthesized and characterized in order to study the variations produced in their optical and electronic properties by linking different (hetero)aromatic electron donor moieties at 4′position of the electron deficient terpyridine moiety. The final donor-acceptor systems 3a-g were synthesized in fair to good yields by Kröhnke condensation of the precursor aldehydes 1, with 2-acetylpyridine 2. Hyper-Rayleigh scattering in dioxane solutions using a fundamental wavelength of 1064 nm was employed to evaluate their second-order nonlinear optical properties. Terpyridine derivative 3g functionalized with the 9-ethyl-9Hcarbazolyl group exhibited the largest first hyperpolarizability (β = 610 × 10 −30 esu, using the T convention) thus indicating its potential application as a second harmonic generation (SHG) chromophore. Terpyridine derivatives 3 were also used as ligands for the synthesis of novel [Ru II (tpy)(NCS) 3 ]complexes, prepared in good yields by a two-step procedure involving the preparation of [Ru III (tpy)(Cl 3 )] as intermediates. Ruthenium II complexes display a broad absorption in the visible range, accounting for their very dark color. Their redox behaviour is mainly characterized by the Ru II -Ru III oxidation and by the ligand-centered reduction, whose potentials can be finely tuned by the electronic properties of the aromatic substituents on the terpyridine ligand. Hyper-Rayleigh scattering in methanol solutions using a fundamental wavelength of 1064 nm was also employed to evaluate their second order nonlinear optical properties.
The dimetallic system [Cu (L)] contains two facing equivalent metallocyclam subunits and incorporates ambidentate anions, mono- (halides) and poly-atomic (sulfate), which bridge the two Cu centres. Isothermal titration calorimetry (ITC) experiments in water showed that the log K values of the inclusion equilibria for halides and sulfate varied over a restricted interval (3.6±0.2), which indicated lack of selectivity and that similarity of ΔG° values resulted from the unbalanced contribution of the ΔH° and TΔS° terms: the more favourable the one, the less favourable the other. In particular, a linear dependence of ΔH° and TΔS° was observed (a typical enthalpy/entropy compensatory diagram), which assigned a major role to hydration terms: 1) a more hydrated anion resulted in a more endothermic dehydration process; and 2) a larger number of water molecules released to the solution resulted in a more positive TΔS°. Limiting cases refer to the complexation 1) of the poorly hydrated iodide (highly exothermic process, entropically disfavoured), and 2) of the highly hydrated sulfate (moderately endothermic process, entropically very favoured). Anion receptors operating in water belong to two main domains: 1) those exhibiting positive ΔH° and positive TΔS° (+/+ signature), and 2) those displaying the opposite behaviour: (-/- signature). The receptor investigated herein connects the two domains, along the ΔH°/TΔS° straight line, thanks to the hidden role of the versatile metal-anion interaction.
Covalent linking of a Ru(terpy)2(2+) substituent improves recognition and sensing properties of the urea subunit toward anions. Urea's anion affinity is enhanced by the electrostatic attraction exerted by the Ru(II) cation and by the electron-withdrawing effect exerted by the entire polypyridine-metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π-π* and MLCT bands of the Ru(terpy)2(2+) chromophore, detected through UV-vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor-anion H-bond complexes in diluted MeCN solution. On (1)H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl(-) ion was observed, taking place through an outer-sphere mechanism. The Ru(terpy)2(2+) substituent favors the deprotonation of a urea N-H fragment on addition of a second equivalent of fluoride, with formation of HF2(-).
The bis-bidentate ligand, obtained from Schiff base condensation of RR-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde (L-L), forms with [Cu(I)(MeCN)4]ClO4 a double strand helicate complex, made especially stable by the presence of four definite interstrand π-π interactions involving a quinoline subunit and a naphthylmethoxy substituent of the two strands. The [Cu(I)2(L-L)2](2+) complex, which does not decompose even on excess addition of either L-L or Cu(I), undergoes a two electron oxidation in MeCN, through two one-electron fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry (CV) studies. The high stability of the mixed valence complex [Cu(I)Cu(II)(L-L)2](3+) with respect to disproportionation to [Cu(I)2(L-L)2](2+) and [Cu(II)2(L-L)2](4+) is essentially due to a favorable electrostatic term. Cu(II) forms with L-L a stable species, with a 1:1 stoichiometric ratio, but, in the absence of crystallographic data, it was impossible to assess whether it is of mono- or dinuclear nature. However, CV studies on an MeCN solution containing equimolar amounts of Cu(II) and L-L showed the presence in the reduction scan of two fully reversible waves, separated by about 250 mV, which indicated the presence in solution of a dicopper(II) double strand helicate complex, [Cu(II)2(L-L)2](4+). This work demonstrates that additional interstrand π-π interactions can favor the formation of unusually stable dicopper(I) and dicopper(II) helicate complexes.
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