A Charge-Transfer Salt Based on Ferrocene/Ferrocenium Pairs and Keggin-Type Polyoxometalates

Abstract

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]·[FeII(Cp)2]·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 π-π interactions that generates rectangular cavities of about 14 × 10 Å in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak OPOM···CMeOH-OMeOH···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 Mössbauer 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···Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished.

Triple the fun: tris(ferrocenyl)arene-based gold(i) complexes for redox-switchable catalysis

“…Notably, all three P-Au-Cl fragments are still intact and form dimers of an overall sixfold positive charge through a set of two aurophilic interactions (d(Au(1)-Au(6)) ¼ 2.989(1)Å, d(Au(2)-Au(4)) ¼ 3.188(1)Å) and a less-close Au/Au contact (d(Au(3)/Au(5)) ¼ 3.397(1)Å). 139 While the poor crystal quality precludes detailed metric analyses, generally larger C 5 H 4 (centroid)-Fe distances of over 1.68Å and, accordingly, Fe-C bond lengths of up to 2.15(2)Å, typical for ferrocenium species, 136,140 are discernible (Table S8 †). Other structural parameters, particularly with respect to the P-Au-Cl moieties are, within error, comparable to the molecular structure of [1c(Au) 3 ].…”

Supramolecular networks supported by the anion...π linkage of Keggin-type heteropolyoxotungstates

“…For comparison, closely related adeninium decavanadate does not preserve any anionÁ Á Á interactions to the metal-oxide surfaces due to domination of the hydrogen-bond andstacking interactions (Sedghiniya et al, 2020). Also, neither pyridinium (Hashimoto & Misono, 1994) nor ferrocenium cations (Artetxe et al, 2018) maintain the anionÁ Á Á interactions with Keggin clusters. The present double amide N-HÁ Á ÁO hydrogen bonds in (2) are topologically meaningful: they generate additional links between the four-connected (a) The [SiW 12 O 40 ] 4À cuboctahedra in the environment of four bridging (blue) and two terminal (green) anionÁ Á Á stacks in the structure of (1).…”