Solid Phases from the Liquid System H₂N(CH₂)₂NH₂  CdBr₂  HBr  H₂O. An X‐ray and ^79,81Br — NQR Study of (H₃N(CH₂)₂NH₃)CdBr₄, (H₃N(CH₂)₂NH₃) (CdBr₃)₂ · H₂O, and (H₃N(CH₂)₂NH₃)₂CdBr₆

Abstract

From the aqueous system ethylenediamine, (en),  CdBr2  HBr  H2O of varying component concentrations, at room temperature the compounds (enH2)CdBr4, (enH2)(CdBr3)2 · H2O, and (enH2)2CdBr6 were crystallized. 79,81Br NQR spectroscopy shows that the three solid phases, crystallized at room temperature, are the stable ones in the temperature range 77 ≤ T/K ≤ 300. (enH2)CdBr4 shows a three line 81Br NQR spectrum, the frequencies lying in the range 53 ≤ v (81Br)/MHz < 68 and having negative temperature coefficients dv/dt over the whole temperature range covered. A phase transition with hysteresis is observed at 340 K. In the high temperature phase I only one 81Br NQR line is observed, with negative temperature coefficient, too. (enH2)(CdBr3)2 · H2O shows also a three line 81Br NQR spectrum, the frequencies lying in the range 38 MHz to 72 MHz at room temperature with positive as well as negative temperature coefficients. (enH2)2CdBr6 reveals a four line 81Br NQR spectrum, three of the lines lying in the range 40 MHz to 70 MHz; the fourth line was observed at frequencies as low as 10 MHz. (enH2)(CdBr3)2 · H2O crystallizes at room temperature monoclinic, space group C2h6‐C2/c with Z = 4 (formula units per unit cell) a = 818 pm, b = 2413 pm, c = 801 pm, β = 107.8°. The structure is characterized by chains of units [Cd4Br12]4. The chains are built up by edge connected octahedra CdBr6 and the corners of two neighbouring octahedra are part of a bridging tetrahedron CdBr4, located alternating cis and trans on the chain. (enH2)2CdBr6 crystallizes also monoclinic, space group C2h2‐P21/m, a = 669 pm, b = 2050 pm, c = 637 pm, β = 93.4°; Z = 4. The structure corresponds to a formulation ((enH2))2(CdBr4)2⊖ · 2Br⊖. In both compounds hydrogen bonding is observed. The NQR results are in full agreement with the crystal structures; structure and bond scheme are discussed.

Novel Series of Ribbon Structures in Dialkylammonium Chlorocadmates Obtained By Dimensional Reduction of the Hexagonal CdCl2 Lattice

“…While there are numerous examples of neutral ribbon structures in the Cambridge Database, only a few structures of compounds containing anionic ribbons have been reported. These include a single chain system in a hydrazinium salt, C 2 H 9 CdCl 2 IN 4 S,18a a double chain in 2-amino-4,5-dihydro-3H + -thiazolium trichlorocadmate,18b and a triple chain in [(C 6 H 5 ) 4 P] 4 Pb 15 I 34 (dmf) 6 18c. In addition, ribbons with widths of four and five cadmium octahedra are found in ( N -ethylethylenediammonium) 2 Cd 4 Cl 12 ·H 2 O and (C 7 H 16 N) 2 [Cd 5 Cl 12 (H 2 O) 2 ]·H 2 O, respectively. 18d,e Given this limited number of anionic structures, continued systematic exploration of these systems will yield a wide variety of new ribbon structures.…”