Neutralmolekülcomplexe' - Structural Characterization of Some Adducts of Urea and Thiourea with N,N'-Bidentate Aromatic Bases

Oepen and Vögtle in 1979 recorded the formation of a number of ‘neutral molecule complexes’ between urea (ur) and/or thiourea (tu) and a number of N,N′-aromatic chelate bases derivative of 2,2′-bipyridine (bpy), motifs now widely utilized in essays in studies of molecular/crystal architecture. The structures are recorded of a number of their adducts, namely (a) bpy/ur (1 : 1), (b) phen/ur (1 : 1), (c) phen/tu (1 : 1), (d) dmp/ur (1 : 1), together with (e) bpy/tu (1 : 1) and (f) a dmp/tu adduct of 1 : 2 stoichiometry (phen = 1,10-phenanthroline; dmp = 2,9-dimethyl-1,10-phenanthroline). Association takes places in all cases by way of hydrogen-bonding interactions between alternating (thio-)urea NH2 groups which form an infinite band with the nitrogen atoms of the aromatic base at the periphery, the base planes quasi-normal to that of the band, as in the archetypical 2,6-lutidine/urea (1 : 1) array, described long ago.