Crystal structures of nitridotechnetium(V) complexes of amine oximes differing in carbon chain lengths

Abstract

Structures of nitridotechnetium(V) amine oxime complexes, [TcN(pnao)(H₂O)][BPh₄] 1, [TcN(bnao)(H₂O)][BPh₄] 2 and [TcN(pentao)(H₂O)][BPh₄] 3 [Hpnao = HONCMeCMe₂NH(CH₂)₃NHCMe₂CMeNOH; Hbnao =  HONCMeCMe₂NH(CH₂)₄NHCMe₂CMeNOH; Hpentao = HONCMeCMe₂NH(CH₂)₅NHCMe₂CMeNOH], differing in carbon chain length of the amine oxime ligands, were characterized by X-ray crystallography. These complexes are six-co-ordinated and distorted octahedral. Four nitrogen atoms of the amine oxime ligands are in the equatorial plane and both the nitrido and H₂O ligands in the apical positions. These complexes have an asymmetrical intramolecular hydrogen bond between the two oxime oxygen atoms. Their intramolecular O· · ·O distances are 2.720 Å in 1, 2.512 Å in 2 and 2.531 Å in 3. The longest O· · ·O distance in 1 is ascribed to a steric effect of the carbon chain length between the amine nitrogens. Namely, the shorter carbon chain of the pnao ligand causes strain on the co-ordinated pnao moiety, and the O· · ·O distance in 1 is longer than that in 2 and 3 with longer carbon chains.