Structural and Computational Studies of 1-Methyl-2-thiocytosine and its Coordination Mode in a Dinuclear Platinum(IV) Complex [(PtMe3)2(μ-1-MeSCy-1κN3,1:2κ2S)2][BF4]2

Abstract

X-Ray diffraction analysis of 1-methyl-2-thiocytosine (1-MeSCy, 1) revealed that its crystals contain two structurally very similar independent molecules (A, B). These molecules are connected through a complex network of hydrogen bonds. Centrosymmetric di- and tetrameric units AAʹ and BAAʹBʹ, respectively, are formed through N-H...N hydrogen bonds (N4a...N3aʹ 3.019(4) Å , AAʹ; N4a...N3b 2.988(4) Å, BAAʹBʹ), and the tetrameric units are connected through N-H...S hydrogen bonds. The arrangement of A and B molecules found in crystals of 1 was confirmed by DFT calculations up to tetrameric BAAʹBʹ units, yielding similar equilibrium structures, and the energies of the N-H...N hydrogen bonds between A and Aʹ and A and B were calculated to be about 10 kcal mol−1. Reaction of 1-MeSCy (1) with [PtMe3(Me2CO)3][BF4] (2) led to the formation of the ionic dinuclear complex [(PtMe3)2(μ-1-MeSCy-1κN3,1:2κ2S)2][BF4]2 (3) which was fully characterized by NMR (1H, 13C, 195Pt) and IR spectroscopy, ESI mass spectrometry and microanalysis. A singlecrystal X-ray diffraction analysis of 3 confirmed the dinuclear structure of the complex. The complex cation consists of a central [Pt2(μ-S)2] core having bound the 1-methyl-2-thiocytosine ligands in a 1κN3,1:2κ2S coordination mode in a face-to-face arrangement, the thionucleobase ligands being present as the amino-thione tautomer.