Structures of dimethylammonium metal(III) sulfate hexahydrates (metal = Al, Cr)

Abstract

I) (Al(H20)613+.C2H8N+.2SO 2-, Mr = 373.28, monoclinic, P21/n, a = 6.408 (1), b = 10.752(1), c= 11.134 (2) A, r= 100.44(1) °, V = 754.4 (2) A 3, Z = 2, Dx = 1.643, Dm= 1.62 g cm -3, A(Mo Ka) = 0.71073 A,/z = 4.7 cm-1, F(000) = 392, T= 295 K, R = 0.040 for 1680 reflections with I> 4tr(I). (II) (Cr(H20)6)3+.C2H8N+.2SO 2-, Mr = 398.29, monoclinic, P2Jn, a=6.391(8), b= 10.748(3), c=ll.40(1)A, fl=100.87(6) °, V= 769 (1) A 3, Z = 2, Dx = 1.720, D m = 1.64 gcm -3, a(Mo Ka) = 0.71073 ,~, /z = 10.5 cm-1, F(000) = 414, T = 295 K, R = 0.038 for 1666 reflections with I > 4tr(/). The A1 and Cr atoms are octahedrally coordinated by the water molecules showing A1--Ow and Cr---Ow bond lengths ranging from 1.874 (2) to 1.891 (2) A and from 1.953 (2) to 1.967 (2) A, respec- tively. The dimethylammonium cations are dis- ordered, with each NH2 group having two centrosymmetric positions. The hydrogen bonds between O atoms of a sulfate anion acting as acceptors, water molecules and a dimethylammo- nium cation acting as a donor range from 2.586 (3) to 2.87 (1) A. Introduction. Trivalent metal cations (most often A13+ and Cr 3+) form not only a variety of double sulfates with univalent alkaline and ammonium cations, but also with univalent guanidinium and