Pt as mediator of strong antiferromagnetic coupling between two Cu-II ionsin a heteronuclear (CuPtCuII)-Pt-II-Cu-II complex of the model nucleobase 1-methylcytosinate

The tetrakis(1-methylcytosine) complex [Pt(1-MeC-N-3)(4)](NO3)(2) (1) in it s head-tail-head-tail (htht) rotamer form binds upon deprotonation of the e xocyclic amino group of 1-MeC, two Cu-II at either side of the central Pt-n to give trinuclear cations [Pt(1-MeC-)(4)Cu2X2](n+) (2) with X = Cl-, H2O, NSC-, N-3(-). X-ray crystal structure analyses of [Pt(1-MeC-)(4)Cu-2(Cl)(1 .6)(H2O)(0.4-). 1.6H(2)O (2a) and [Pt(1-MeC-)(4)Cu2-(H2O)(2)](NO3)(2). 3H(2 )O (2b) reveal short Cu-Pt distances of 2.519(2)- 2.531(2) Angstrom. These compounds are diamagnetic as a result of the strong exchange interaction (J = 980 +/- 30 cm(-1) (2a)), despite a separation of approximately 5 Angstro m between the Cu-II centers. MO considerations are in agreement with the as sumption that Pt-II acts as a mediator between the two Cu-II centers. A sec ond trinuclear complex derived from the hhhh rotamer of 1 containing both C o-III and Na+ [Pt(1-MeC-)(4) Co(H2O)Na](NO3)(2). 2H(2)O (3) has been isolat ed in very low yield and characterized by X-ray structure analysis. The Com center is bound to four amide N atoms and forms a bond to Pt (2.402(2) Ang strom), whereas the Na+ ion is bound to the four oxygen atoms of the nucleo base, A general route for the preparation of heteronuclear MPtM and MPtM' c ompounds is described.