Long chain secondary dithiooxamides as ligands for the synthesis of platinum(II) metallomesogens

In the search for platinum complexes of secondary dithiooxamides (RNHCS)(2) (termed as R2H2DTO), showing metallomesogens properties, several [Pt(R2HDTO)(2)] were synthesised starting from cis-[Pt(Me2SO)(2)Cl-2]. The paper is mainly devoted to the co-ordination chemistry of long chain dithiooxamides which in some cases show a different behaviour with respect to R2H2DTO bearing small substituents on nitrogen atoms. The observed reactivity appears related only in part to the lower basicity of amide nitrogen atoms in diaryl- with respect to dialkyl-dithiooxamides, and differently populated conformations of the complexes seem to play an important role. Mesophase formation far [Pt(R2HDTO)(2)] with R=3,4-[CH3(CH2)(9)O](2)C6H3 and 3,4-[CH3(CH2)(11)O](2)C6H3 is suggested by polarising optical microscopy and differential scanning calorimetry. The synthesis of analogous bis-chelates, but with two different dithiooxamide ligands, is also described.