Stacking eclipsed

Fig. 3. Alignment of the radical cations in the SbCls salt. (Viewed along stack, eclipsed units not shown.)...

The TCNQ molecule in [TR(bzim)]2-TCNQ is sandwiched between two units of [ J,-N, C -bzimAu]3 in a face-to-face manner so that it is best represented by the formula (7t-[ J,-N, C -bzimAu]3)( j,-TCNQ)(7t-[p-N, C -bzimAu]3). The cyanide groups clearly are not coordinated to the gold atoms. The distance between the centroid of TCNQ to the centroid of the AU3 unit is 3.964 A. The packing of [TR(bzim)]2-TCNQ shows a stacked linear-chain structure with a repeat pattern of-(Au3)(Au3)(p-TCNQ) (Au3)(Au3)(p-TCNQ)- an ABBABB repeat The complex [TR(bzim)]2-TCNQ contains two very short intermolecular Au Au distances of 3.152 A (identical for the two aurophilic bonds). The intermolecular Au Au distance is even shorter than the intramolecular distances in the starting compound, which are 3.475, 3.471, and 3.534 A. The adjacent AU3 units in [TR(bzim)]2-TCNQ form a chair-type structure rather than the face-to-face (nearly eclipsed) pattern reported in Balch s studies of the nitro-9-fluorenones adducts with the trinuclear Au(I) alkyl-substituted carbeniate complexes. 

Fig. 8 Local transmission pictures in a superposed benzenoid structure. As the two rings change geometry from an eclipsed pseudo para geometry (upper left) through an eclipsed pseudo meta geometry to a slip-stacked structure to a single tunneling pathway, the transmission at the Fermi energy increases hy roughly a factor of ten. Reprinted with permission from G. C. Solomon et al. J. Am. Chem. Soc. (2010) 132, 7887-7889. Copyright 2011 American Chemical Society...

The cyclic group 14 polyanions are usually found in ternary materials that contain two types of cations which, in addition to providing charge balance, perform different roles. The structures typically consist of cyclic polyanions that are stacked in an eclipsed fashion to form columns. One type of cation coordinates to the anions and separates them within the column, whereas the second type segregates the columns. These ternary materials are typically prepared by heating stoichiometric amounts of the three elements in an unreactive metal tube, e.g. niobium, at very high temperatures (>800°C) followed by slow annealing at lower temperatures. 

Another case of major enantiomer separation occurs when helical tubuland diols (Section 3.2.1) are crystallised with small phenol molecules and intimately hydrogen bonded co-crystals are produced. A typical example is (11 ) ( p-chloro-phenol) [33], The major supramolecular synthon is H-0 H-0 H-0 hydrogen bonding with eclipsed stacks of the participating molecules surrounding a pseudo-threefold screw axis (Figure 13). This chiral motif involves molecules of p-chloroplienol and only one of the enantiomers of 11. 

Fig. 2 Molecular structure of a model F8BT(top) TFB(bottom) polymer heterojunction in the eclipsed stacking configuration, see also Fig. 3. In the actual polymer, the residues are R = C8Hi2 in the calculations reported here, R = H was used (Adapted from Ref. [43]).

Since intermolecular interactions at the interface play a key role, two representative interface structures were considered, which will be referred to as eclipsed (E) vs. staggered (S), see Fig. 3. These structures correspond to attractive vs. repulsive 7r-stacked interface configurations, which result from the following stacking patterns in the lowest-lying exciton state ... 

Fig. 3 TFB F8BT structures (slightly tilted forward) showing two different orientations of the polymer constituents. In each, the FBT (top chain) consists of 3 fluorene (F) units and 3 benzothiadiazole (BT) units while the TFB (bottom chain) consists of 3 F units and 2 triarylamine (TB) units. These co-monomer units are labeled with indices. The eclipsed orientation (panel a) has the middle F units (F12 and F22) of both chains 7r-stacked while the staggered orientation (panel b) has the middle BT of FBT (BT2) and the middle F of TFB (F22) 7r-stacked, see Eqs. (l)-(2). Reprinted with permission from Ref. [41]. Copyright 2007, American Institute of Physics.

Of the metallophthalocyanines that crystallize in forms other than the a-, j3-, and y-polymorphs, the most notable are Pb(pc)2031 and Ga(pc)F1301. The Pb(pc) molecules are stacked metal-over-metal, as shown in Fig. 28, and the Pb-Pb spacing is 3.73 A. The phthalocyanine ring deviates markedly from planarity, although the separate isoindole moieties retain their planarity. In Ga(pc)F the Ga atoms are symmetrically bridged by F, with a Ga-F distance of 3.92 A the pc rings are eclipsed, rather than staggered1301. 

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