Preparation of some platinum-linked acridines and crystal structure of [3,6-bis(dimethylamino)acridinioethyl]chloro-(N,N,N′,N′-tetramethylethylenediamine)platinum(II) perchlorate

Abstract

The cationic platinum complex [Pt(η²-C₂H₄)Cl(tmen)]⁺1(tmen =N,N,N′,N′-tetramethylethylenediamine) reacted with acridines {3,6-diaminoacridine [proflavine, NC₁₃H₇(NH₂)₂] and 3,6-bis(dimethylamino)-acridine [acridine orange, NC₁₃H₇(NMe₂)₂]} to give platinum species in which the metal is linked to the polycyclic molecule by an ethylene chain. In the case of acridine orange the attack occurs at the endocyclic nitrogen giving the complex [Pt{CH₂CH₂NC₁₃H₇(NMe₂)₂}Cl(tmen)]⁺2 which is in equilibrium with the starting species. On the contrary, in the case of proflavine the attack occurs preferentially at the exocyclic aminic groups leading to the formation of [{PtCl(tmen)}₂{HNC₁₃H₇(NHCH₂CH₂)₂}]⁺3, which does not dissociate into its constituents. In 3 each NH₂ group of the incorporated proflavine molecule has lost a proton, one of them has been taken up by the endocylic nitrogen, the other by an extra molecule of proflavine. Crystals of 2, obtained from a dichloromethane solution, were characterized by X-ray crystallography: space group P2₁/n, a= 7.700(4), b= 25.446(3), c= 14.858(6)Å, β= 99.08(2)° and Z= 4. The refinement converged to R= 0.0572. The co-ordination around platinum is essentially square planar and the co-ordination plane makes an angle of 29.2(4)° with the plane of the acridine moiety. The acridine rings are infinitely stacked in a head-to-tail fashion. The plane-to-plane distance is about 3.5 Å and the closest Pt ⋯ Pt distance is 5.178(2)Å.