Reactions of K₂[Fe₃Q(CO)₉] (Q = Se, Te) with AsI₃: Synthesis and Structures of the First {Fe₃TeAs} Clusters with Capping µ₃-AsI and Bridging µ₆,κ³:κ³-As₂ Ligands

Reactions of cluster salts K₂[Fe₃Q(CO)₉] (Q = Se, Te) with AsI₃ in CH₂Cl₂ proceed differently depending on the chalcogen atom and the reaction conditions. For Te, the product of addition of μ₃-AsI vertex to the initial cluster, [Fe₃(CO)₉(μ₃-Te)(μ₃-AsI)] (2b) is the main component of the solution. By action of traces of water, such as wet silica gel, 2b is converted to a dimeric cluster [{Fe₃(CO)₉(μ₃-Te)}₂(μ₆,κ³:κ³-As₂)] (5), whose molecules contain two identical square-pyramidal cores joined by diarsane moiety. For Se, the product 2a, analogous to 2b, was only found on the basis of mass-spectra, as main component of the reaction solution, but could not be separated because of its instability and similarity of its properties to those of [Fe₃(CO)₉Se₂], a by-product. Two other products, [Fe₃(CO)₉(μ₃-Se)(µ₄,κ³:κ²-AsSe)Fe₂(CO)₆(μ-I)] (3) and K[{Fe₃(CO)₉(μ₃-Se)(μ₄-As)}₂Fe(CO)₃I] (4) were only found as little amount of crystals. The molecule of 3 consists of the pyramidal {Fe₃SeAs} core linked by the As–Se bond to a {Fe₂SeI} fragment. The cluster anion in 4 consists of two {Fe₃SeAs} cores joined via the {Fe(CO)₃I} unit. The products 3 and 4 presumably originate from the dissociation of the initial cluster core and their formation correlates with lower stability of Se-containing cluster 2a as compared to 2b.