TAUTOMERIC WATER LAYERS - FORMATION AND STRUCTURE OF LOW-MELTING TRIHYDRATES OF TRIETHYLAMINE AND 4-METHYLPYRIDINE

Low-melting trihydrates of triethylamine (Et(3)N) and 4-methylpyridine (4-MePy) have been confirmed and detected by phase analysis and the crystal structures determined. Both are monoclinic with space group P2(1)/c and Z = 4 formula units per unit cell. The lattice parameters are a = 13.606, b = 6.291, c = 12.412 Angstrom, and beta = 99.47 degrees at -100 degrees C for Et(3)N.3 H2O, and a = 9.982, b = 6.877, c = 12.958 Angstrom, and beta = 103.50 degrees at -90 degrees C for 4-MePy.3 H2O. The water molecules in the two structures are hydrogen-bonded in condensed four-, five-, and six-membered rings with 1:2:1 ratio, thus forming characteristic layers parallel (100) of identical topology and tautomeric to each other. The amine molecules are linked to both sides of the layers by O similar to H...N bonds from different O atoms.