The fluorosulfur containing pincer ligands 1,3-(CH 2 SR f ) 2 C 6 H 4 [R f = C 6 F 5 (1) and 4-HC 6 F 4 (2)] and 1,2,4,5-(CH 2 SR f ) 4 C 6 H 2 [R f = C 6 F 5 (3) and 4-HC 6 F 4 (4)] have been prepared by treatment of 1,3-(CH 2 Br) 2 C 6 H 4 or 1,2,4,5-(CH 2 Br) 4 C 6 H 2 with the corresponding lead thiolate Pb(SR f ) 2 .

Two different counter-ion-free host-guest complexes have been prepared and isolated. These compounds were formed from two equally and opposite doubly-charged species, the viologen guests 1 a(2+) and 1 b(2+) and the anti-disulfodibenzo[24]crown-8 [DSDB24C8](2-) host, which gave rise to the 1:1 neutral complexes [1 a⋅DSDB24C8] and [1 b⋅DSDB24C8]. These species are held together by hydrogen bonding and π stacking, as well as strong electrostatic interactions. The investigation of these neutral ion-paired supramolecular systems in solution and in the solid state allowed us to establish their co-conformational preferences. Compound [1 a⋅DSDB24C8], with small methyl groups as substituents on the viologen unit, may adopt three different geometries, 1) an exo nonthreaded, 2) a partially threaded, and 3) a threaded arrangement, depending on the relative spatial orientation between the host and guest: The partially-threaded structure is preferred in solution and in the solid state. The presence of bulky tert-butylbenzyl groups in the viologen moiety in compound [1 b⋅DSDB24C8] restricts the possible geometrical arrangements to one: The exo nonthreaded arrangement. This structure was confirmed in the solid state by X-ray crystallography. The stability of the neutral complexes in solution was determined by UV/Vis spectrophotometry. The stoichiometry of the complexes was established by continuous variation experiments, and overall equilibrium constants and ΔG° values were determined on the basis of dilution experiments. The results observed are a consequence of only the intrinsic stability of the complexes as there are no additional contributions from counter ions.

The use of the electrostatic stoppersc oncept in the fieldo fm echanically interlocked molecules is reported;t hese stoppers are chemically sensitive end groupso n al inear guest molecule that allows for the conversion of a pseudo-rotaxane speciesi nto ar otaxanec omplex by a changei nt he medium acidity.T he chemicals timulus causes the appearanceo fn egative chargeso nb oth ends of the linear component, passing from cationic to anionic, and causing as ignificant ring-to-axle electrostatic repulsion. This phenomenon has two different and simultaneous effects:1 )destabilizes the complexa saconsequence of confining an anionic ring into an anionic axle, and 2) increasest he dissociatione nergyb arrier, thus impeding ring extrusion. This newly formed metastable rotaxane species is resistant to solventa nd temperature effects and performs as at wo-state degenerated molecular shuttle in solution.

Platinum(ii) derivatives of the tridentate ligand Ph2PCH2CH2P(Ph)CH2CH2PPh2 (triphos), including [Pt(SRF)(triphos)](CF3SO3) RF = C6F4CF3-4 1, C6F52, C6HF4-4 3, C6H4CF3-4 4, C6H3F2-2,4 5, C6H4F-2 6, C6H4F-4 7 and C6H58, have been prepared and characterised.

Metathesis reactions employing lead fluorothiolates and C6H4‐1,3‐(CH2Br)2 afford the corresponding pincer‐type dithioether ligands C6H4‐1,3‐(CH2SRf)2 [Rf = C6H4F‐2 (L1), C6H4F‐3 (L2), C6H4F‐4 (L3), C6H4CF3‐2 (L4), C6H4CF3‐3 (L5), and C6H4CF3‐4 (L6)]. A series of PdII pincer‐type complexes [PdCl(κ3‐Ln)], 1 to 6, were prepared and fully characterized. The X‐ray diffraction molecular structures of C6H4‐1,3‐[CH2S(C6H4F‐4)]2 (L3), [PdCl(SCS–C6H4F‐2)] (1), [PdCl(SCS–C6H4F‐3)] (2), [PdCl(SCS–C6H4F‐4)] (3), [PdCl{SCS–C6H4(CF3)‐2}] (4), and [PdCl{SCS–C6H4(CF3)‐4}] (6) are also reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A new series of linear molecules derived from 1,2-bis(imidazopyridin-2-yl)ethane can fully or partially penetrate the cavity of the dibenzo-24-crown-8 macrocycle to produce a new family of host-guest complexes. Protonation or alkylation of the nitrogen atoms on the pyridine rings led to an increase in the guest total positive charge up to 4+ and simultaneously generated two new recognition sites (pyridinium motifs) that are in competition with the 1,2-bis(benzimidazole)ethane motif for the crown ether. The relative position of the pyridine ring and the chemical nature of the N-substituent determined the preferred motif and the host-guest complex geometry: (i) for linear guests with relatively bulky groups (i.e., a benzyl substituent), the 1,2-bis(benzimidazole)ethane motif is favored, leading to a fully threaded complex with a [2]pseudorotaxane geometry; (ii) for small substituents, such as -H and -CH3 groups, regardless of the guest shape, the pyridinium motifs are preferred, leading to external partially threaded complexes in a 2:1 host to guest stoichiometry.

No abstract

The forces that bind the components of a host-guest complex to generate a stable supramolecular system are noncovalent interactions. The enthalpy of this association, ΔH°, usually measured using calorimetry, quantifies the magnitude of such interactions and is directly related to the stability of the supramolecular complex formed. Using Calvet calorimetry to determine the enthalpies of solution and reaction in water, the enthalpy of association was derived for a supramolecular system formed by the anionic macrocycle anti-disulfodibenzo[24]crown-8 ([DSDB24C8]) and the dicationic guest paraquat [PQT]. The calorimetric results show an exothermic association process, which indicates the generation of strong interactions between the components of the ion pair. This is consistent with the formation of a stable supramolecular complex [PQT][DSDB24C8], whose spatial arrangement in aqueous solution is proposed based on spectroscopic analysis.