Three pentacoordinate complexes of the type [Co­(pypz)­X2], where pypz is a tridentate ligand 2,6-bis­(pyrazol-1-yl)­pyridine and X = Cl– (1), NCS– (2), and NCO– (3), have been synthesized, and their structures have been determined by X-ray analysis. The DC magnetic data show a sizable magnetic anisotropy, which was confirmed by high-field high-frequency electron paramagnetic resonance (HF EPR) measurements. Well-resolved HF EPR spectra of high spin cobalt (II) were observed over the microwave frequency range 100–650 GHz. The experimental spectra of both complexes were simulated with axial g tensor components, a very large positive D value, and different E/D ratios. To determine the exact D value for 2 (38.4 cm–1) and 3 (40.92 cm–1), the far-infrared magnetic spectroscopy method was used. Knowledge of the zero field splitting parameters and their signs is crucial in interpreting the single-molecule magnet or single chain magnet behavior. The AC susceptibility data confirm that these complexes exhibit a slow magnetic relaxation under small applied DC field with two (1 and 3) or three (2) relaxation modes.

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The presented research is focused on the synthesis of alloyed Ag−In−Zn−S colloidal nanocrystals from a mixture of simple metal precursors such as AgNO 3 , InCl 3 , zinc stearate combined with 1-dodecanethiol (DDT), 1-octadecene (ODE), and sulfur dissolved in oleylamine (OLA). In particular, the focus is on the effect of the solvent (ODE vs 1,2dichlorobenzene (DCB)) and the type of sulfur precursor (S/ OLA vs S/n-octylamine (OCA)) on the metal precursors reactivates and on the chemical composition, crystal structure, and luminescent properties of the resulting nanocrystals. The replacement of ODE by DCB as a solvent lowers the reactivity of metal precursors and results in a 3-fold decrease of the photoluminescence quantum yields (Q.Y.) values (from 67% to 21%). This negative effect can be fully compensated by the use of S/OCA as a source of sulfur instead of S/OLA (Q.Y. increases from 21% to 64%). NMR studies of the isolated organic phase indicate that the S/OLA precursor generates two types of ligands being products of (Z)-1-amino-9-octadecene (OLA) hydrogenation. These are "surface bound" 1-aminooctadecane (C 18 H 37 NH 2 ) and crystal bound, i.e., alkyl chain covalently bound to the nanocrystal surface via surfacial sulfur (C 18 H 37 -NH-S crystal). Highly luminescent Ag−In−Zn−S nanocrystals exhibit a cation-enriched (predominantly indium) surface and are stabilized by a 1-aminooctadecane ligand, which shows more flexibility than OLA. These investigations were completed by hydrophilization of nanocrystals obtained via exchange of the primary ligands for 11-mercaptoundecanoic acid, (MUA) with only a 2-fold decrease of photoluminescence Q.Y. in the most successful case (from 67% to 31%). Finally, through ligand exchange, an electroactive inorganic/organic hybrid was obtained, namely, Ag−In−Zn−S/7-octyloxyphenazine-2-thiol, in which its organic part fully retained its electrochemical activity.

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A new indium precursor, namely, indium(II) chloride, was tested as a precursor in the synthesis of ternary Ag−In−S and quaternary Ag−In−Zn−S nanocrystals. This new precursor, being in fact a dimer of Cl 2 In−InCl 2 chemical structure, is significantly more reactive than InCl 3 , typically used in the preparation of these types of nanocrystals. This was evidenced by carrying out comparative syntheses under the same reaction conditions using these two indium precursors in combination with the same silver (AgNO 3 ) and zinc (zinc stearate) precursors. In particular, the use of indium(II) chloride in combination with low concentrations of the zinc precursor yielded spherical-shaped (D = 3.7−6.2 nm) Ag−In−Zn−S nanocrystals, whereas for higher concentrations of this precursor, rodlike nanoparticles (L = 9−10 nm) were obtained. In all cases, the resulting nanocrystals were enriched in indium (In/Ag = 1.5−10.3). Enhanced indium precursor conversion and formation of anisotropic, longitudinal nanoparticles were closely related to the presence of thiocarboxylic acid type of ligands in the reaction mixture. These ligands were generated in situ and subsequently bound to surfacial In(III) cations in the growing nanocrystals. The use of the new precursor of enhanced reactivity facilitated precise tuning of the photoluminescence color of the resulting nanocrystals in the spectral range from ca. 730 to 530 nm with photoluminescence quantum yield (PLQY) varying from 20 to 40%. The fabricated Ag−In−S and Ag−In−Zn−S nanocrystals exhibited the longest, reported to date, photoluminescence lifetimes of ∼9.4 and ∼1.4 μs, respectively. It was also demonstrated for the first time that ternary (Ag−In− S) and quaternary (Ag−In−Zn−S) nanocrystals could be applied as efficient photocatalysts, active under visible light (green) illumination, in the reaction of aldehydes reduction to alcohols.