Iso-propyl-ammonium halidometallates. I. [CoX 4]2-·X - (X = Cl, Br), ZnCl4 2-, and [ZnCl3 -] n salts.

An exploration of the iso-propyl-ammonium (IPA+) metal halide structural space is conducted, initially, for cobalt(II) and zinc(II) halides as a counterpart to the more extensively studied metal halide systems containing the isomeric tri-methyl-ammonium cation. For cobalt(II) halides, the only compound obtained from slow evaporation of acidic aqueous solutions of iso-propyl-ammonium halide and cobalt(II) halide is (IPA+)3CoX 4·X (X = Cl, Br), namely, tris-(iso-propyl-ammonium) tetra-chlorido-cobaltate(II) chloride, (C3H10N)3[CoCl4]Cl, and tris-(iso-propyl-ammonium) tetra-bromido-cobaltate(II) bromide, (C3H10N)3[CoBr4]Br, regardless of the starting stoichiometric ratio of (IPA+)X:CoX 2. These structures consist of isolated tetra-hedral CoX 4 2- complexes and X - ions separated by IPA+ cations. One IPA+ cation hydrogen bonds to two complexes and to two halide ions to produce clusters. These clusters form stacks with hydrogen bonding from the remaining IPA+ cations linking the stacks into a tight, three-dimensional network. A 2:1 molar ratio of (IPA+)Cl and ZnCl2 under similar growth conditions readily yields crystals of bis-(iso-propyl-ammonium) tetra-chlorido-zincate(II), (C3H10N)2[ZnCl4] or (IPA+)2ZnCl4, consisting only of IPA+ cations and isolated ZnCl4 2- tetra-hedra. This despite the expectation of common structural chemistry for the similarly sized Co2+ and Zn2+ ions with 51 known isostructural A2CoCl4 and A2ZnCl4 compounds out of 54 for the same monopositive A cation. Growth from a 1:1 ratio of (IPA+)Cl:ZnCl2 yields crystals of poly[iso-propyl-ammonium [[di-chlorido-zincate(II)]-μ-chlorido]], {(C3H10N)[ZnCl3]} n or (IPA+)ZnCl3, in which parallel chains of corner-sharing ZnCl4 tetra-hedra are separated by IPA+ cations. This unusual zinc(II) halide chain structure has previously been observed only in [YCH2(CH3)3N]ZnCl3 salts (Y = H, halogen). In contrast to these known compounds, which are found in polar ortho-rhom-bic space groups, the structure reported here is in ortho-rhom-bic Pbca.