A novel hydrogen-bonded cyclic dibromide in an organic diammonium salt

The organic diammonium salt N,N-dibenzyl-N,N,N,N-tetramethylethylenediammonium dibromide dihydrate, (dbtmen)Br22H2O (1), was prepared by the reaction of N,N,N,N-tetramethylethylenediamine (tmen) with benzyl bromide. 1 crystallizes in the triclinic space group P1 with the following unit cell dimensions for C20H34Br2N2O2 (M = 494,31): a = 8,6672(6) Å, b = 11,7046(8) Å, c = 11,7731(8) Å, alpha = 76,988(8), beta = 88,978(8), g = 76,198(8), V = 1129,26(13) Å3, Z = 2. Three components, namely the (dbtmen)2+ dication, two bromide anions and two crystal water molecules constitute the structural arrangement of 1. H2O molecules are linked to bromide anions via O–H BR hydrogen bonding interactions resulting in the formation of a four-membered {O2Br2} cyclic dibromide. The {O2Br2} units and the dications are arranged as alternating layers extending in the crystallographic bc plane. The arrangement of anions and cations may be viewed as a typical lamellar structure. The crystal water molecules can be removed by heating 1 at 140C and the anhydrous dibromide thus formed can be fully rehydrated as evidenced by IR spectra and X-ray powder patterns.