INFLUENCE OF COORDINATION ON N-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-X(-) HYDROGEN-BONDS .2. ZN(NH3)(2)BR-2 AND NI(NH3)(2)X(2) (X IS CL- AND BR-)

Microcrystalline samples of Zn(NH3)(2)Br-2 and Ni(NH3)(2)X(2) (X is Cl - and Br-) have been investigated from 100 to 293 K using X-ray diffra ction and IR spectroscopy measurements (range 400-4000 cm(-1)) perform ed with isotopically dilute (5% deuterated) samples. Values of Delta n u(ND)/Delta T for all compounds hint at the existence of hydrogen bond s. Zn(NH,),Br, shows The dynamics of ammonia molecules even at 100 K, and no indications are apparent that dynamic disorder of ammonia molec ules takes place in Ni(NH3)(2)X(2) (X is Cl- and Br-). A comparison be tween octahedrally coordinated ammoniates [Ni(NH3)(6)]Br-2, Ni(NH3)(2) Br-2 and [Zn(NH3)(6)]Br-2 with tetrahedrally coordinated ones [Zn(NH3) (2)Br-2] leads to the conclusion that the lower coordination number in creases the strength of the hydrogen bonds. Because this effect is sma ll, it is not possible to separate the influence of the type of coordi nating ions for one coordination number from the influence of the coor dination number itself.