Ruthenium(II/III) mediated transformation of 1,2-bis-(2'-pyridylmethyleneimino)benzene (L) to 2-(2'-benzimidazolyl)pyridine (L'H) and its in situ formed complexes with Ru(II) : X-ray structure of trans-[Ru(PPh3)2(L'H)2](ClO4)2