ISOLATED VERSUS CONDENSED ANION STRUCTURE - THE INFLUENCE OF THE CATION SIZE AND HYDROGEN-BOND ON STRUCTURE AND PHASE-TRANSITION IN MX(4)(2-) COMPLEX SALTS - 2,2-DIMETHYL-1,3-PROPANEDIAMMONIUM TETRABROMOCADMATE(II) MONOHYDRATE, DIMETHYLAMMONIUM TETRABROMOZINCATE(II), AND DIMETHYLAMMONIUM TETRABROMOCADMATE(II)

In the course of work on the anion condensation of Cd and Zn halides, the crystal structures and Br-79,Br-81 NQR spectra of 2,2-dimethyl-1,3 -propanediammonium tetrabromocadmate(II) monohydrate (1) and dimethyla mmonium tetrabromozincate(II) (2), and Br-79,Br-81 NQR spectra of dime thylammonium tetrabromocadmate(II) (3) have been studied. An isolated [CdBr4](2-) ion of the salt [H3NCH2C(CH3)(2)CH2NH3]CdBr4 . H2O (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. [(CH3)(2)NH2]2ZnBr4 (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, beta = 121.84(1)degre es. The Br-81 NQR spectrum of (1) is a quartet (v in MHz, T = 77 K/ 30 3 K): v(1) = 68.403/64.278; V-2 = 65.296/62.663; v(3) = 56.525/54.660; v(4) = 43.211/45.422. The Br-81 NQR spectrum of (2) is a quartet too (v in MHz, T = 77 K/300 K): v(1) = 66.848/64.784; v(2) = 63.152/ 61.88 3; v(3) = 57.498/55.890; v(4) = 49.416/50.224. The Br-81 NQR spectrum of [(CH3)(2)NH2]2CdBr4 (3) is also a quartet (v in MHz, T = 77 K/310 K ): v(1) = 68.606/67.272; v(2) = 65.806/63.296; v(3) = 58.096/ 57.369; v(4) = 55.757/53.393. The change of NQR frequencies with temperature i s smooth for all three compounds. One of the Br-81 NQR Lines in both ( 1) and (2) increases slightly in frequency with increasing T. In the c ompound (1), the H2O coordinates to NH3+ groups and to bromines formin g a distorted tetrahedron (Br...)(2) H2O (... HN)(2), the six angles l ying between 69 degrees and 131 degrees. The relations between the bro mine NQR and the crystal structures are discussed for the title compou nds.