Crystal chemistry of uncharged phosphazene bases .2. Structures of the anhydrous form and two hydrates of the diphosphazene (Me(2)N)(3)P=N-(Me(2)N)(2)P=NH

The uncharged, very strong diphosphazene base (Me(2)N)(3)P=N-(Me(2)N)(2)P=NH (for short P-2) and two hydrates have been characterized by crystal structure analysis. The diphosphazene, m. p. 23 degrees C, is triclinic with space group <P(1)over bar> and Z=2 formula units per unit cell of dimensions a=7.595, b=7.972, c=14.642. Angstrom, alpha=100.19 degrees, beta=96.15 degrees and gamma=100.79 degrees at -150 degrees C. A monohydrate, P-2 . H2O, m.p. 24 degrees C, is monoclinic with P2(1)/c, Z=4, a=11.778, b=15.415, c=10.190 Angstrom, and beta=93.46 degrees at -100 degrees C. Another hydrate, P-2 . 2.25H(2)O, m.p. 14 degrees C, is also monoclinic with P2(1)/c, Z=8, a=10.348, b=25.476, c=15.791 Angstrom, and beta=105.70 degrees at -100 degrees C. In the structure of the anhydrous diphosphazene then are no distinct intermolecular interactions. In the hydrate P-2 . H2O, a centrosymmetric dimer of the formula unit is formed by hydrogen bonds O-H ... N arranged in a centrosymmetric four-membered ring. In the hydrate P-2 . 2.25 H2O, hydrogen bonding O-H ... O and O-H ... N generates an aggregate of live four-membered rings, alternating with a single water molecule in an unlimited chain. In spite of the high basicity of the diphosphazene, its hydrate structures are not ionic but clearly molecular.