Intermolecular interactions, xanthate structures

There are two types of objects in supramolecular chemistry supermolecules (i.e., well-defined discrete oligomolecular species that result from the inter-molecular association of a few components), and supramolecular arrays (i.e., polymolecular entities that result from the spontaneous association of a large, undefined number of components) (4, 5). Both are observed in some metal-xanthate structures to be described herein. The most frequent intermolecular forces leading to self-assembly in metal xanthates are so-called secondary bonds . The secondary bond concept has been introduced by Nathaniel W. Alcock to describe interactions between molecules that result in interatomic distances longer than covalent bonds and shorter than the sum of van der Waals radii (6). Secondary bonds [sometimes called soft-soft interactions (7)] are typical for heavier p-block elements and play an important role as bonding motifs in supramolecular organometallic chemistry (8). Other types of intermolecular forces (e.g., Ji- -ji stacking) are also observed in the crystal structures of metal xanthates. 

There is no apparent correlation between the magnitude of the intermolecular Au- -O or Au- -S interaction and the distortion from the ideal linear geometry about the gold atom. For example, the structure of (o-MeCgH PAu CO—i-Pr) (141) features the closest intramolecular Au- - -O contact of 2.892(7) A, but the smallest deviation from linearity [i.e., 179.6(1)°]. This emphasizes the weak nature of these intramolecular interactions. As for the nickel xanthates, there are... 

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