The thermal reaction of hexacarbonylchromium with the polycyclic aromatic hydrocarbons (PAHs) pyrene, perylene, chrysene and 1,2‐benzanthracene has afforded four organometallic complexes of the type [(η6‐PAH)Cr(CO)3], whose unprecedented structures were obtained by single‐crystal X‐ray analysis. The topology of the coordination of the Cr(CO)3 fragment and its asymmetry with respect to the coordinating ring may depend on the opportunity to maintain the maximum aromaticity of the complexed ligand. DFT calculations, 1H NMR, FT‐IR and Raman spectroscopy have been used to elucidate the type of interaction between the PAH ligand and the carbonylmetal moiety, giving insight into the ligand‐to‐metal donor capacity and the intra‐ and intermolecular interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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The optimization of the physico-chemical properties of both Gd(III) chelates and nanocarriers is of great importance for the development of effective nanosystems for magnetic resonance imaging (MRI) applications. With this aim, macrocyclic Gd(III) chelates were selectively attached to the pendant amino groups exposed to the external surface of spheroidal mesoporous silica nanoparticles (MSNs). This was achieved by treating the metal complexes with MSNs that contained the templating surfactant molecules confined within the silica channels (hexadecyltrimethylammonium (CTA)/MSN), followed by extraction of the surfactant. The nanoparticles showed greatly improved (1)H relaxometric efficiency relative to corresponding systems that also feature Gd(III) chelates conjugated inside the pores. A further significant relaxivity enhancement was observed after chemical transformation of the free amino groups into amides. The ionic relaxivity of the final nanoparticles (r(1p) =79.1 mM(-1) s(-1); 0.5 T, 310 K) is one of the highest reported so far.

Three solid molecular complexes of fluorene with electron-withdrawing tetracyanoethylene, 1,2,4,5tetracyanobenzene and 7,7,8,8-tetracyanoquinodimethane were synthesized. Single-crystal X-ray diffraction data elucidated the order-disorder aspects of the crystal structures ascribed to the different molecular symmetries of the employed building blocks. This hypothesis was confirmed by the structural and energetic results of ab initio periodic calculations. Donor-acceptor solid state interactions between molecular counterparts have been highlighted by electron and vibrational IR and Raman solid state spectroscopy, indicating a significant extent of electron density transfer from the fluorene unit towards the cyano-molecules. The experimental evidences of donor-acceptor interactions between molecular counterparts were compared to the lattice energies and solid state band-gaps, obtained by periodic calculations, and to the cluster HOMO-LUMO differences, obtained by isolated cluster calculations. A good agreement between spectral and theoretical data was found.