1915-85-1

Four new Ru(ii) polypyridyl complexes that contain an extended aromatic moiety derived from pyrazino[2,3-h]dipyrido[3,2-a:2′,3′-c]phenazine and either 1,10-phenanthroline (phen) or 1,4,5,8-tetraazaphenanthrene (TAP) have been synthesized, their solid state X-ray crystal structure determined and their photophysical and biological properties evaluated. Their interactions with DNA have been studied, and they have been tested for their potential as photodynamic therapeutic (PDT) agents in the treatment of cancer. A practical modification of a method by Carter, Rodriguez and Bard has been introduced and used to calculate binding parameters for the complexes which show a strong affinity for DNA with binding constants in the order of 107 M1 (in 10 mM phosphate buffer). The complexes containing phen as an ancillary ligand become emissive upon binding to DNA (“light switch effect”), but do not show selective cytotoxicity upon light irradiation. On the other hand, the TAP complexes, which show an inverse “light switch effect” (emission quenched upon binding to DNA), are strongly photo-toxic suggesting their use in Photodynamic Therapy (PDT). In HeLa cells the best PDT agent shows an IC50 value (light) = 4 μM vs. IC50 value (dark) = 62 μM.

The first synthesis of benzo[1,2-c:3,4- c′]bis[1,2,5]selenadiazole has been developed starting from commercially available 4-nitrobenzo-2,1,3- selenadiazole. Improved syntheses of the related heterocycles [1,2,5]selenadiazolo[3,4-e]-2,1,3-benzothiadiazole, furazanobenzo-2,1,3- thiadiazole and furazanobenzo-2,1,3-selenadiazole are also reported.

Stable radical anions of bis(thiadiazolo)-p-benzoquinone as well as of bis- and tris(thiadiazolo)benzene derivatives form on one-electron reduction using potassium/ cryptand in THF solution.According to the assigned ESR spectra, their electron-rich sulfur centers exhibit especially large spin populations.On addition of THF soluble alkalimetal salts, the ESR signals vanish, whereas with metal hexacarbonyls Me(CO)6 paramagnetic mono- (Me = W) and di(metalpentacrbonyl) (Me = Cr, Mo, W) complexes result, for which HMO-McLachlan calculations suggest preferred coordination at the N centers of the same thiadiazol bridge.

The X-ray structure analyses of the title compounds 1 and 2 were performed. 1: monoclinic, C2/c, a = 9.532(2), b = 11.469(2), c = 7.030(3) Angstroem, β = 110.58(2) deg, Z = 4; 2: monoclinic, P21/a, a = 7.650(2), b = 7.729(2), c = 12.948(3) Angstroem, β = 74.26(2) deg, Z = 4.The structure of 1 was solved by direct methods, that of 2 by Patterson- and successive Fourier-synthesis techniques.The least squares refinement converged for 894 independent reflections with I>2?I to an R-value of 0.032 (Rw = 0.035) in the case of 1 and for 1440 independent reflections to on R-value of 0.045 (Rw = 0.045) in the case of 2.The bond lengths in the thiadiazole rings in 1 and 2 and also in the Se-homologous ring in 2 indicate to a quasi-aromatic ?-system, whereas the aromatic character of the central benzene ring in 1 and 2 is strongly disturbed.The substitution of one S by the homologous Se in 2 induces significant changes of comparable bond lengths in 1 and 2.In the crystal structures of both compounds molecular layers and columnar stacks are formed.Quasi-polimers in form of ribbon like structures are established in 1 by short S***N contacts and in 2 by short Se***N contacts.In 2 (SeN2)x-chains are formed. - Key words: Chalkogen-Diimides, Thia(selena)diazoles, quasi-Aromatic ?-Systems, Columnar Structures, Intermolecular S(Se)***N Contacts