Heterocyclic N-oxide CH center dot center dot center dot O hydrogen bonding (part 3). Crystal packing of 2,2 '-bipyridine-1,1 '-dioxide and pyridine N-oxide

Short intermolecular CH ... O contacts of 2.212(2) and 2.325(2) Angstrom ar e found in the crystal structure of 2,2'-bipyridine-1,1'-dioxide (BPDO) and are assigned as CH ... O hydrogen bonds based on geometric criteria and qu antum mechanical calculations. The pattern of BPDO association yields a two -dimensional CH ... O hydrogen-bonded array in the BPDO crystal. Each BPDO molecule participates in eight CH ... O hydrogen bonds, which occur in two distinct pairs as centric R-2(2)(8) and acentric R-2(2)(12) dimeric linkage s whose binding enthalpies are estimated to be -6.7 and -2.3 kcal mol(-1), respectively, by AM1 calculations. Self-association via CH ... O hydrogen b onding of the parent molecule, pyridine N-oxide (PO), is also considered. I n solution, PO molecules are postulated to form CH ... O bonded R-2(2)(8) d imers with an estimated binding energy of -5 to -8 kcal mol(-1). In the cry stal, PO molecules associate to give a three-dimensional network via CH ... O hydrogen-bonding. (C) 1999 Elsevier Science Ltd.