The formation of inclusion complexes between cucurbit[7]uril (CB[7]) and ferrocene and its derivatives has been investigated. The X-ray crystal structure of the 1:1 inclusion complex between ferrocene and CB[7] revealed that the guest molecule resides in the host cavity with two different orientations. Inclusion of a set of five water-soluble ferrocene derivatives in CB[7] was investigated by 1H NMR spectroscopy and calorimetric and voltammetric techniques. Our data indicate that all neutral and cationic guests form highly stable inclusion complexes with CB[7], with binding constants in the 10(9)-10(10) M(-)(1) and 10(12)-10(13) M(-1) ranges, respectively. However, the anionic ferrocenecarboxylate, the only negatively charged guest among those surveyed, was not bound by CB[7] at all. These results are in sharp contrast to the known binding behavior of the same guests to beta-cyclodextrin (beta-CD), since all the guests form stable inclusion complexes with beta-CD, with binding constants in the range 10(3)-10(4) M(-1). The electrostatic surface potentials of CB[6], CB[7], and CB[8] and their size-equivalent CDs were calculated and compared. The CD portals and cavities exhibit low surface potential values, whereas the regions around the carbonyl oxygens in CBs are significantly negative, which explains the strong affinity of CBs for positively charged guests and also provides a rationalization for the rejection of anionic guests. Taken together, our data suggest that cucurbiturils may form very stable complexes. However, the host-guest interactions are very sensitive to some structural features, such as a negatively charged carboxylate group attached to the ferrocene residue, which may completely disrupt the stability of the complexes.

Synthetic ratiometric fluorescent probes are useful to detect metal cations and anions.

Communications interaction between i) radical spins, J p±p , and ii) radical and cobalt spins, J p±Co , must be considered. None of these is strong enough to give striking effects at room temperature, e.g., strong exchange narrowing or line broadening due to fast relaxation processes. However, as T C is lower in the radical-based compounds, it appears that the sandwiched radical layer is actually counteracting the driving interaction for the bulk ferromagnetic ordering.The similarities in the physicochemical characterization of the three compounds allow any significant structural modification between the radical derivatives and the precursor compound to be excluded. The dipolar interaction H dip is assumed to be the driving interaction for the setting up of bulk ferromagnetism within the three compounds, as demonstrated for alkyl-carboxylate parent compounds. [20] It involves the in-plane spin±spin correlation function, which diverges critically as the layers order, thus promoting bulk ferromagnetism for the three materials. The lowering of the critical temperature for Co-rad1 and Co-rad2 compared to Co-prec1 must be attributed to the presence of the radical spins, since the interlayer distance is much the same in the various compounds. Among the possible mechanisms, it can be stated that the radical spins do not simply line up within the internal field created when the cobalt(II) layers order, otherwise the net magnetic moment would increase up to saturation more rapidly for the radical derivatives. Moreover, the lowering of T C cannot be understood within this scheme. Therefore, the observed effects are more likely due to the exchange interaction J p±Co . The cobalt(II) layers including the radical spins must order at lower temperature than the radical-free compound, due to the effect of J p±Co .In this respect, this new class of hybrid magnets differs markedly from the classical intercalated layer compounds, mostly because both sub-networks (inorganic and organic) are in strong interaction. This is very promising for the future design of multifunctional materials in which the properties of the organic and inorganic networks are in close synergy.