Stable Cu(I) complexes with thioamidoguanidine possessing halide-bridge structure

Abstract

Treatment of an aryl-sec-alkyl unsymmetrical thiourea (Tu) with Cu^IIX₂ (X = I, Br) transform the thiourea (Tu) into a thioamidoguanidino (Tag) moiety with concomitant reduction of Cu^II to Cu^I, which forms a [Cu₂^I(μ₂-X)₂Tag₂] (X = I (for A) and X = Br (for B)) complex. Meanwhile, the treatment of same unsymmetrical thiourea (Tu) with Cu^IX (X = Br) forms a stable cluster with a [Cu^I₃(μ₂-S)₄Tu₄X₃] core (C). Single crystal X-ray diffraction revealed that compounds A and B exhibit 1D chain with a Cu₂(μ₂-X)₂ core, whereas compound C is a Cu^I₃S₄Br₃ cluster. Compound A is centrosymmetric due to the trans orientation of two Tag units whereas compound B is ascentric due to the cis orientation of two Tag units. In compound A, the Cu₂I₂ core is perfectly rhomboidal where the iodine atoms are trans oriented. However in compound B, the Cu₂Br₂ core is not perfectly rhomboidal (bowl shaped) and the bromine atoms are cis oriented. It is interesting to note that although the Tag moiety in compounds A and B contain two morpholine-O atoms; only one of the morpholine-O atoms (O₂) is involved in the generation of three-dimensional network. The Cu^I₃S₄Br₃ cluster in compound C contains one tri- and two tetra-coordinated Cu^I centers. The Cu^I cluster in C contains a Cu₂(μ₂-S)₂ rhomboidal plane exhibiting a chair and a boat form containing the Cu^I₃S₃ unit. In compounds A and B, the two Cu^I centers are μ₂-X bridged and have a μ₁-S linkage, whereas in compound C the linkages are opposite having four μ₂-S bridges and three μ₁-Br linkages.