(−)-N,N′-Bis[(1S,2R,5S)-6,6-dimethyl-bicyclo[3.1.1]heptan-2-ylmethyl]pyridine-2,6-dicarboxamide monohydrate

The title compound, C27H39N3O2·H2O, is a chiral pyridine-2,6-dicarboxamide derivative including cis-myrtanyl groups as amine substituents. The pyridine-2,6-dicarboxamide core approximates C 2 point symmetry and a solvent water molecule lies on the pseudo-twofold axis. The water molecule serves both as acceptor and donor for efficient hydrogen bonds involving N—H and C=O functional groups as donor and acceptor groups, respectively. As a result, each water molecule in the crystal structure is tetrahedrally bonded to three symmetry-related molecules, forming a three-dimensional supramolecular network. Such an arrangement is a common feature found in the majority of X-ray-characterized symmetrically substituted pyridine-2,6-dicarboxamide derivatives.

The title compound, C 27 H 39 N 3 O 2 ÁH 2 O, is a chiral pyridine-2,6dicarboxamide derivative including cis-myrtanyl groups as amine substituents. The pyridine-2,6-dicarboxamide core approximates C 2 point symmetry and a solvent water molecule lies on the pseudo-twofold axis. The water molecule serves both as acceptor and donor for efficient hydrogen bonds involving N-H and C O functional groups as donor and acceptor groups, respectively. As a result, each water molecule in the crystal structure is tetrahedrally bonded to three symmetry-related molecules, forming a three-dimensional supramolecular network. Such an arrangement is a common feature found in the majority of X-ray-characterized symmetrically substituted pyridine-2,6-dicarboxamide derivatives.
(-)-N,N'-Bis[(1S,2R,5S)-6,6-dimethyl-bicyclo[3.1.1]heptan-2-ylmethyl]pyridine-2,6-dicarboxamide monohydrate S. Bernès, F. J. Pérez-Flores and R. Gutiérrez Comment Nowadays, reactions conducted in the absence of solvents under mild reaction conditions are becoming an important method in laboratories worldwide as an environment-friendly technique for the efficient syntheses of organic molecules. The main advantages of solvent-free organic synthesis are shorter reaction times, minimum waste and generally higher yields, operational simplicity as well as reduction of thermal degradative byproducts along with cleaner work-up (Tanaka & Toda, 2000). As part of an ongoing program aiming to develop simpler and eco-friendly methods for organic transformations under solvent-free conditions (Tovar et al., 2007;Vázquez et al., 2004), we engaged the preparation of chiral pincer ligands (Pérez-Flores & Gutiérrez, 2008). The title compound resulted from this research, by introducing chiral cis-myrtanyl groups as amine substituents.
The X-ray characterized monohydrate has the expected molecular geometry (Fig. 1). The pyridine-2,6-dicarboxamide core approximates a C 2 point symmetry, with the pseudo 2-fold axis passing through N1 and C24. The guest water molecule O3 is placed on the pseudo 2-fold axis and is involved in two N-H···O hydrogen bonds within the asymmetric unit ( Fig. 1 and Table 1, lines 1 and 2). The same water molecule is a donor group for two C═O···H intermolecular hydrogen bonds of relatively strong strength (Table 1, lines 3 and 4). As a consequence, a three-dimensional supramolecular structure is formed in the crystal structure, with water molecules being bonded in a tetrahedral arrangement (Fig. 2) to three symmetry-related molecules. Such a feature seems to be common for symmetrically substituted pyridine-2,6-dicarboxamide derivatives.
These compounds are generally crystallized as hydrates, and, at least for X-ray characterized compounds, water molecules form hydrogen bonds similar to those observed in the title molecule (e.g. Yu et al., 1999;Qi et al., 2002;Jain et al., 2004;Odriozola et al., 2004).

Refinement
C-bonded H atoms were placed in idealized positions and refined with a riding model approximation. Constrained C-H distances: 0.93 (aromatic CH), 0.96 (methyl CH 3 ), 0.97 (methylene CH 2 ) or 0.98 Å (methine CH). Isotropic displacement parameters: U iso = 1.5U eq (carrier C atom) for methyl groups and U iso = 1.2U eq (carrier C atom) otherwise. Methyl groups were considered as rigid rotating groups. Other H atoms (amine groups and water molecule) were found in a difference map and refined freely. Measured Friedel pairs (287)