Isolated versus Condensed Anion Structure: the Influence of the Cation Size and Hydrogen Bond on Structure and Phase Transition in MX4 2- Complex Salts. 2,2-Dimethyl-1,3-propanediammonium Tetrabromocadmate(II) Monohydrate, Dimethylammonium Tetrabromozincate(II), and Dimethylammonium Tetrabromocadmate(II)

Abstract In the course of work on the anion condensation of Cd and Zn halides, the crystal structures and 79,81 Br NQR spectra of 2,2-dimethyl-1,3-propanediammonium tetrabromocadmate(II) monohydrate (1) and dimethylammonium tetrabromozincate(II) (2), and 79-81 Br NQR spectra of dimethyl-ammonium tetrabromocadmate(II) (3) have been studied. An isolated [CdBr 4 ] 2- ion of the salt [H 3 NCH 2 C(CH 3 ) 2 CH 2 NH 3 ]CdBr 4 • H 2 O (1) is formed, with polar orthorhombic space group Pbc2 1 , Z = 4, a = 645.5(3), b = 1628.3(8), c -1389.5(6) pm. [(CH 3 ) 2 NH 2 ] 2 ZnBr 4 (2) has also an isolated anion lattice, with monoclinic space group, P2 1 /c, Z = 4, a = 870.6(3), b = 1195.6(4), c = 1628.9(5) pm, β = 121.84(1)°. The 81 Br NQR spectrum of (1) is a quartet (ν in MHz, T = 77 K/ 303 K): ν 1 = 68.403/64.278; ν 2 = 65.296/62.663; ν 3 = 56.525/54.660; V 4 = 43.211/45.422. The 81 Br NQR spectrum of (2) is a quartet too (ν in MHz, T= 77 K/300 K): ν 1 = 66.848/64.784; ν 2 = 63.152/ 61.883; ν 3 = 57.498/55.890; ν 4 = 49.416/50.224. The 81 Br NQR spectrum of [(CH 3 ) 2 NH 2 ] 2 CdBr 4 (3) is also a quartet (ν in MHz, T =77 K/310 K): ν 1 = 68.606/67.272; ν 2 = 65.806/63.296; ν 3 = 58.096/ 57.369; ν 4 = 55.757/53.393. The change of NQR frequencies with temperature is smooth for all three compounds. One of the 81 Br NQR lines in both (1) and (2) increases slightly in frequency with increasing T. In the compound (1), the H 2 O coordinates to NH 3 + groups and to bromines forming a distorted tetrahedron (Br...) 2 ...H 2 O... (... HN) 2 , the six angles lying between 69° and 131°. The relations between the bromine NQR and the crystal structures are discussed for the title compounds.