Comparative analysis of M–O, M–S and cation–π(arene) interactions in the alkali metal (Na⁺, K⁺, Rb⁺, Cs⁺) bis-dithiocarbamate salts of N,N′-dibenzyl-1,2-ethylenediamine

The alkali metal (Na⁺, K⁺, Rb⁺, Cs⁺) bis-dithiocarbamate (bis-dtc) salts of N,N′-dibenzyl-1,2-ethylenediamine have been prepared from the reaction of N,N′-dibenzyl-1,2-ethylenediamine with carbon disulfide in the presence of two equivalents of the corresponding alkali metal hydroxide. Additionally, the analogous triethylammonium derivative has been obtained. The resulting compounds have been analyzed as far as possible by elemental analysis, FAB⁺ mass spectrometry, IR, UV-Vis and NMR (¹H, ¹³C) spectroscopy, and single-crystal X-ray diffraction, showing that the composition of the metal salts can be described by the general formula [{[(H₂O)_xM-µ-(H₂O)_yM(H₂O)_x][bis-dtc]}_n] (1, M = Na⁺, x = 3, y = 2; 2, M = K⁺, x = 1, y = 2; 3, M = Rb⁺, x = 0, y = 1; 4, M = Cs⁺, x = 0, y = 1; 5, M = Et₃HN⁺, x = 0, y = 0). The solid-state and solution studies showed that all alkali metal ions participate in the formation of M–O and cation-π(arene) interactions, while M–S interactions are only observed for the larger alkali metals K⁺, Rb⁺ and Cs⁺. As expected, within the alkali metal group there is a clear tendency for a decreasing number of M–O bonds in favor of M–S and cation–π(arene) interactions, however, only K⁺ forms a semi-sandwich type complex with η⁶-coordination.