Dedicated to Dr. Antoine Skoulios on the occasion of his 65th birthday
The preparation and study of fullerene derivatives are being intensively pursued, with the aim of generating new supramolecular assemblies and advanced materials. [1] Incorporation of fullerenes into thin ordered films appears as an important issue in the applications of this carbon allotrope. [2] However, monolayers of fullerene itself at the air ± water interface are difficult to achieve due to strong fullerene ± fullerene interactions and three-dimensional aggregation, and all attempts to create defined Langmuir ± Blodgett (LB) multilayers of fullerenes have failed. [3, 4] Whereas functionalization of the fullerene sphere with hydrophilic addends leads to significant improvements, [4, 5] fullerene derivatives with good spreading characteristics and reversible compression/ expansion behavior are quite rare. [6, 7] In a collaborative work among the research groups of Diederich, Stoddart, Echegoyen, and Leblanc, dendrimers with a fullerene core and peripheral acylated glucose units have been investigated. [6] These derivatives show reversible behavior of fullerene monolayers in successive compression/decompression cycles, the dendritic portion preventing the irreversible aggregation of the N-Pt-N and N-Pt-O angles for approaches I and II, respectively, as shown for 2 in Figure 1. To assess the effect of nuclear relaxation, we reoptimized the geometry of 2 during H 2 O approach II at the E MP2 minimum (Pt ´´´O 3.5 ). The energy gain from nuclear relaxation amounted to À 0.05 kcal mol À1 and was considered negligible. The geometry of the systems was therefore not re-optimized. The basis set superposition error (BSSE) was evaluated using the counterpoise method [22,23] for the approaches I/2 and II/2. For the interactions of 1, the BSSE was assumed to be the same as for the corresponding approach of 2 at the same Pt ´´´O distance. The atomic charges used for the estimation of E ES were determined from fits to the MP2 electrostatic potential for the isolated species using the Merz ± Kollman routine [24] implemented in GAUS-SIAN 94, with a van der Waals radius of 2.3 for Pt. A check calculation using the CHELPG routine [25] yielded only slightly different E ES curves. The CCDC crystal structures (Figures 3,4) were drawn using the program Insight II. [26]