Crystal Structure and Magnetic Properties of Bis(N,N-dimethyl-2-thiophenemethylammonium) Tetrabromocobaltate(II)

Abstract

Considerable interest has been shown over recent years in the transition metal halide complexes, and, among them, the tetrahalometalates with various organic countercations have been the subject of theoretical, 1-3 structural, 4-8 magnetostructural 9-14 and spectroscopic 15-17 studies. The magnetostructural relation in the tetrabromocuprate with various organic countercations has been intensively studied, and in view of the magnetic properties of these compounds, the BrBr contact and the Cu-Br-Cu bridge are known to be quite important; 18,19 the antiferromagnetic coupling in the series of tetrabromocuprate compounds is produced via a ‘two-halide’ Cu-BrBr-Cu contact while the ferromagnetic coupling is through a ‘single-halide’ Cu-Br-Cu bridge. The hydrogen bonding 20,21 and noncovalent π-interaction between the aromatic rings of organic cations 13,22 in this type of molecules control molecular recognitions and self-assembly processes, and exercise important effects on the solid-state structure and the properties of many compounds relevant to biological and material sciences. 23-25 Despite the structural similarities between the tetrabromocuprates and the tetrabromocobaltate complexes, the magneto-structural studies for the tetrabromocobaltate complexes and other cobalt(II) compounds have been rarely reported. In this work, we report the crystal structure and magnetic behaviors of the (dmamtH)2CoBr4 complex. The 2-(N,Ndimethylaminomethyl)thiophene (dmamt) base contains an amine group and an aromatic thiophene ring, and therefore we expected that the protonated base dmamtH + as a cation might play an important role in stabilizing the solidstate structure of the (dmamtH) 2CoBr4 complex. The magnetic behavior of the (dmamtH)2CoBr4 complex was investigated to confirm the importance of the Br Br separation for two-bromide super-exchange pathways in the complex. ExperimentalSection The (dmamtH)2CoBr4 was prepared from a direct reaction between 2-(N,N-dimethylaminomethyl)thiophene·HBr, (dmamtH)Br and anhydrous cobalt(II) bromide. The (dmamtH)Br salt was prepared from a reaction of 2-(N,N-dimethylaminomethyl)thiophene (dmamt) (6 mmol) with an excess of concentrated hydrobromic acid in 50 mL of ethanoltriethylorthoformate mixture solvent (5 : 1 v/v). 3 mmol of cobalt(II) bromide was dissolved in 10 mL of ethanoltriethylorthoformate (5 : 1 v/v). This solution was added into a (dmamtH)Br solution. The solution was heated with stirring for 5 h, and then allowed to cool in an ice bath. The precipitates were isolated by filtration and washed with cold ethanol. The blue single crystals were obtained by recrystalization in acetonitrile. The yield of the product was 1.38 g (69.38%) based on CoBr2. Anal. Calcd. for CoC14H24Br4N2S2: