Technetium(V) and rhenium(V) complexes of biguanide derivatives. Crystal structures

Biguanidine ligands HLn (HL1=1,1- dimethylbiguanide, HL2=1- phenethylbiguanide, HL3=1- phenylbiguanide) formed disubstituted cationic oxo- and nitrido-complexes [MO(HLn)(2)](3+) (M=Tc or Re) and [TcN(HLn)(2)(H2O)](2+). They are characterised by the presence of a network of N-H ... X (X=Cl or H2O) intra- and inter- molecular hydrogen bonds. The imido precursor of Re-V [Re(NMe)(PPh3)(2)Cl-3] formed monosubstituted complexes [Re(NMe)(HL1,2)(PPh3)Cl](2+). In alkaline solutions deprotonation of ligands occurs and monocationic, disubstituted oxo- and imido-species [MO(L-n)(2)](+) (M=Tc or Re), [Re(NCH3)(L-1,L-3)(2)](+) and neutral nitrido complexes [TcN(L-n)(2)] are obtained. Elemental analyses, FT-IR and NMR spectroscopy and conductivity measurements are consistent with the proposed formulations. Crystal structures of [TcO(L-1)(2)](+) and [TcN(HL1)(2)(H2O)](2+) were determined. The former shows a square pyramidal geometry in which the C-N bond distances are equivalent and indicative of pi delocalisation on the chelate ring. The latter displays a pseudo-octahedral geometry with a water molecule trans to the Tc=N multiple bond. The C-N bond distances inside the ligands (1.30 and 1.38 Angstrom) are consistent with single and double bond character, and less pi delocalisation through the whole ligands.