The crystal and molecular structures of two isostructural complexes: [(H₃O•18-crown-6)₂(ZnCl₄)] and [(H₃O•18-crown-6)₂(MnCl₄)]

Abstract

New macrocycle polyether 18-crown-6 complexes of stoichiometry [(H 3 O + •18-crown-6) 2 (MC 4 2− )] have been synthesized for M = Zn and Mn. The two complexes are isostructural and crystallize in the monoclinic system, space group C2/c. The unit cell dimensions are as follows: a = 16.229(9), b = 11.535(3), c = 20.134(8) Å, β = 97.55(4)° and a = 16.255(6), b = 11.625(3), c = 20.122(8) Å, β = 96.54(3)° for the Zn and Mn complexes respectively. In both crystal structures (final R w = 0.048 with 1817 reflections for Zn and R w = 0.074 with 728 reflections for Mn), the crown ether molecule and the H 3 O + cation to which it is hydrogen-bonded are disordered over two sites. The MCl 4 2− anions, which have tetrahedral coordination, are on crystallographic twofold axes of rotation. The Mn—Cl and Zn—Cl distances average 2.270 and 2.361 Å respectively. The hydronium cation, H 3 O + , has pyramidal coordination. Of the two disordered crown ether molecules in the Zn and the Mn complexes, one has a slightly deformed (ttg) 6 conformation while the other one may be described as having the distorted (ttg) 5 (ttc) conformation. These observations are in agreement with the infrared analyses of the complexes. Keywords: 18-crown-6 complexes, hydronium ion, ZnCl 4 2− , MnCl 4 2− , crystal structure.