Abstract
C2h-symmetrical tetranuclear metallacycles {[M(en)(CN)]4}(NO3)4 with M = PdII (4) and PtII (5) have been prepared upon reacting M(en)(CN)2 [M = PdII (1), PtII (2)] with [M(en)(H2O)2](NO3)2. Replacement of the nitrate anions of 5 by terephthalate anions yields the corresponding salt 5a. The X-ray crystal structures of 1, 4, 5, and 5a have been determined. In the metallacycles 4, 5, and 5a the four metals form almost ideal squares with average M···M distances of ca. 5.05 Å (5, 5a) and 5.08 Å (4) along the sides. As shown by 1H NMR spectroscopy, the Pt square 5 is stable in aqueous solution, whereas the Pd square 4 undergoes rearrangement reactions upon aging or the presence of other Pd species such as (bpy)PdII. Preliminary studies on the possibility of non-covalent interactions of 4 and 5 with model nucleobases in water reveal that only 5 is useful in this respect. According to the concentration-dependence 1H NMR study, there is an interaction with the purine base 9-ethyladenine, molecular details of which are unclear at this stage, however. Compound 4 is substitutionally labile and is transformed into the coordination compound 8 with 1-methylcytosine. Two more side products, produced during the various reactions carried out, were characterized by X-ray crystallography: [Pt(en)2][Pt(CN)4] (3) and [Pd(bpy)(en)](SO4)·3H2O (7).
Galstyan, A