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We report herein on a new platform for synthesizing stable, inert, and dispersible metal-free single-chain nanoparticles (SCNPs) via intramolecular metal-traceless azide–alkyne click chemistry. It is well known that SCNPs synthesized via Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) often experience metal-induced aggregation issues during storage. Moreover, the presence of metal traces limits its use in a number of potential applications. To address these problems, we selected a bifunctional cross-linker molecule, sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD). DIBOD has two highly strained alkyne bonds that allow for the synthesis of metal-free SCNPs. We demonstrate the utility of this new approach by synthesizing metal-free polystyrene (PS)-SCNPs without significant aggregation issues during storage, as demonstrated by small-angle X-ray scattering (SAXS) experiments. Notably, this method paves the way for the synthesis of long-term-dispersible, metal-free SCNPs from potentially any polymer precursor decorated with azide functional groups. We gratefully acknowledge Grant PID2021-123438NB-I00 funded by MCIN/AEI/10.13039/501100011033; “ERDF A way of making Europe”, Grant TED2021-130107A-I00 funded by MCIN/AEI/10.13039/501100011033; Unión Europea “NextGenerationEU/PRTR” and Grant IT-1566-22 from Eusko Jaurlaritza (Basque Government).

A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (FeIII) cations and one ferrocene (FeII) molecule per plenary Keggin anion in the crystal structure of [FeIII (Cp)2]4[SiW12O40]&middot, [FeII(Cp)2]&middot, 2CH3OH (1). Compound 1 thus constitutes the first example in the literature in which ferrocenium and ferrocene species coexist in the structure of a polyoxometalate-based salt. The two crystallographically independent ferrocenium species in the asymmetric unit of 1 exhibit different configurations: One displays an eclipsed conformation with ideal D5h symmetry, whereas the conformation in the other one is staggered D5d. The crystal packing of 1 can be best described as an organometallic sub-lattice of ferrocenium and ferrocene species linked by a network of &pi, &pi, interactions that generates rectangular cavities of about 14 &times, 10 &Aring, in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak OPOM&middot, &middot, CMeOH-OMeOH&middot, OPOM type hydrogen bonds. The charge-transfer nature of the salt has been studied by solid-state diffuse reflectance UV-Vis spectroscopy and the presence of magnetically isolated FeIII/FeII centres has been confirmed by M&ouml, ssbauer spectroscopy. A topological study carried out on all of the pristine ferrocenyl species deposited in the Cambridge Structural Database (CSD) has allowed two main conclusions to be drawn: (1) these species tend to adopt extreme conformations (either eclipsed or staggered) with less than a 15% of examples showing intermediate states and (2) the oxidation state of the iron centres can be unequivocally assigned on the basis of a close inspection of the Fe&middot, Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished.

Three new hybrid inorganic-metalorganic compounds containing Keggin-type polyoxometalates, neutral copper(II)-picolinate complexes and guanidinium cations have been synthesized in bench conditions and characterized by elemental analysis, infrared spectroscopy and single-crystal X-ray diffraction: the isostructural [C(NH2)(3)](4)[{XW12O40}{Cu-2(pic)(4)}] . [Cu-2(pic)(4)(H2O)](2) .6H(2)O [X = Si (1), Ge (3)] and [C(NH2)(3)]8[{SiW12O40}(2){Cu(pic)(2)}3{Cu-2(pic)4(H2O)}(2)] .8H(2)O (2). The three compounds show a pronounced two-dimensional character owing to the structure-directing role of guanidinium. In 1 and 3, layers of [{XW12O40}{Cu-2(pic)(4)}] n(4n-) hybrid POM chains and layers of [Cu-2(pic)(4)(H2O)] complexes and [C(NH2)(3)](+) cations pack alternately along the z axis. The hydrogen-bonding network established by guanidinium leads to a trihexagonal tiling arrangement of all copper(II)-picolinate species. In contrast, layers of [C(NH2)(3)](+)-linked [{SiW12O40}(2){Cu(pic)(2)}(3)] n(8n-) double chains where each Keggin cluster displays a {Cu-2(pic)(4)(H2O)} moiety pointing at the intralamellar space are observed in 2. The thermal stability of 1-3 has been studied by thermogravimetric analyses and variable temperature powder X-ray diffraction. Compounds 1 and 3 undergo single-crystal to single-crystal transformations promoted by reversible dehydration processes and the structures of the corresponding anhydrous phases 1a and 3a have been established. Despite the fact that the [Cu-2(pic)(4)(H2O)] dimeric complexes split into [Cu( pic)(2)] monomers upon dehydration, the packing remains almost unaltered thanks to the preservation of the hydrogen-bonding network established by guanidinium and its associated Kagome-type lattice. Splitting of the dimeric complexes has been correlated with the electron paramagnetic resonance spectra. This work was funded by Eusko Jaurlaritza/Gobierno Vasco (grant IT477- 10 and predoctoral fellowship to A. P.), Ministerio de Economia y Competitividad (grant MAT2013-48366-C2-2P) and Universidad del Pais Vasco UPV/EHU (grant UFI11/53). Technical and human support provided by SGIker (UPV/EHU) is gratefully acknowledged.