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The first in situ micro-Raman spectroscopic study of prehistoric drawings found in the cave of Rouffignac-Saint-Cernin (Dordogne, France) was carried out. Rouffignac cave art, assigned to the upper Magdalenian Paleolithic period (13500–12000 bp), is constituted of more than 250 drawings and engraving including 158 mammoths. There are about a hundred drawings, all made of black pigments. Until now, destructive chemical analyses performed on one sample, as well as recent micro X-ray fluorescence (μ-XRF) in situ analyses have shown that the drawings contain manganese oxides. Because no carbon has yet been found, no direct dating of the drawings could be performed. This new study of the Rouffignac cave using non-destructive in situ micro-analyses aims at confirming or not the absence of carbon-based drawings and at understanding the apparent homogeneity of the parietal representations by the identification of the crystalline phases constituting the black pigments. The adaptability of portable equipment as well as the feasibility of in situ micro-Raman analyses in a cave environment was tested. The results obtained are compared with in situ XRF, and X-ray diffraction microanalysis is performed at the same time in the cave. We demonstrate that a portable Raman instrument is very useful to analyze non-destructively drawings in the following difficult conditions: high humidity, various wall geometries, and small amounts of material studied. These results show that the black manganese oxides romanechite and pyrolusite were used as pigments by prehistorical artists. Carbon and carotenoids have been found locally. Differences between the various figures are highlighted and hypotheses about the drawings production are proposed. Copyright © 2012 John Wiley & Sons, Ltd.

The present study refers to a variety of reduced metal-oxide core-shell hybrids, which are unique with regard to their electronic structure, their geometry, and their formation. They contain spherical {Mo(72)Fe(30)} Keplerate-type shells encapsulating Keggin-type polyoxomolybdates based on very weak interactions. Studies on the encapsulation of molybdosilicate as well as on the earlier reported molybdophosphate, coupled with the use of several physical methods for the characterization led to unprecedented results (see title). Upon standing in air at room temperature, acidified aqueous solutions obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid, and molybdosilicic acid led to the precipitation of monoclinic greenish crystals (1). A rhombohedral variant (2) has also been observed. Upon drying at room temperature, compound 3 with a layer structure was obtained from 1 in a solid-state reaction based on cross-linking of the shells. The compounds 1, 2, and 3 have been characterized by a combination of methods including single-crystal X-ray crystallography, magnetic studies, as well as IR, Mossbauer, (resonance) Raman, and electronic absorption spectroscopy. In connection with detailed studies of the guest-free two-electron-reduced {Mo(72)Fe(30)}-type Keplerate (4) and of the previously reported molybdophosphate-based hybrids (including (31)P NMR spectroscopy results), it is unambiguously proved that 1, 2, and 3 contain non-reduced Keggin ion cores and reduced {Mo(72)Fe(30)}-type shells. The results are discussed in terms of redox considerations (the shell as well as the core can be reduced) including those related to the reduction of "molybdates" by Fe(II) being of interdisciplinary including catalytic interest (the Mo(VI)/Mo(V) and Fe(III)/Fe(II) couples have very close redox potentials!), while also referring to the special formation of the hybrids based on chemical Darwinism.

The synthesis, structure and magnetic properties of the first thiooxoverdazyl metal complex (Cu(hfac) 2 (Svdpy)] [hfac = (1,1,1,5,5,5)-hexafluoroacetylacetonate; Svdpy = 1,5-dimethyl-3-(2-pyridyl)-6-thiooxoverdazyl] is described. The organic radical acts as a bidentate ligand leading to a six-coordinate metal complex. The fit of the thermal variations of the magnetic susceptibility reveal a ferromagnetic intramolecular exchange interaction. This finding is confirmed and analysed by using wavefunction-based methods which indicate that the exchange interaction is governed by the substituent of the radical rather than by its heteroatom.