Complexes of the terdentate N-donor ligand 6-(2-aminophenyl)-2,2′-bipyridine (L): crystal structures of mononuclear [ZnL 2][PF 6] 2 and tetranuclear [{CuL(MeCN)} 4( μ4-PO 4)][PF 6] 5 containing an unusual μ4-bridging phosphate ion

• Published in: Inorganica Chimica Acta 1998, Vol.267 (2), p.239-247
• Main Authors: Cargill Thompson, Alexander M.W., Bardwell, David A., Jeffery, John C., Ward, Michael D.
• Format: Article
• Language: English
• Subjects: Copper complexes; Crystal structures; Phosphate bridged complexes; Zinc complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(97)05619-3

The new ligand 6-(2-aminophenyl)-2,2′-bipyridine (L) was prepared in high yield by demethylation of 6-(2- N, N-dimethylaminophenyl)-2,2′-bipyridine, and contains two pyridyl donors and one aniline donor. It coordinates as a terdentae N-donor ligand to both first-row and second-row transition-metal ions. The crystal structure of [ZnL 2][PF 6] 2·MeOH reveals that each ligand coordinates meridionally to give a pseudo-octahedral geometry, with the Zn-aniline bonds (2.20 and 2.26 Å) being on average slightly longer than the Zn-pyridyl bonds (2.11–2.19 Å) and the phenyl rings of the coordinated aniline fragments twisted by ∼40° with respect to the coordinated bipyridyl fragments. Similar complexes [ML 2][PF 6] 2 form with a variety of first-row transition metals, but during recrystallisation of [CuL 2][PF 6] 2 from McCN/diethyl ether small amounts of crystalline [(CuL(MeCN)] 4( μ 4-PO 4)][PF 6] 5·4MeCN were formed which was also crystallographically characterised. This complex contains four {CuL(MeCN)} 2 fragments linked by a central μ 4-phosphate ion which donates one oxygen to each copper centre, and is doubly unusual because (i) this is the first discrete coordination complex containing a μ 4-phosphate bridge, and (ii) the phosphate ion has arisen from complete metal-catalysed hydrolysis of a [PF 6] ion. The electrochemical and spectroscopic properties of [Ru(terpy)L][PF 6] 2 show that the aniline group is a stronger electron donor and a weaker-field ligand than a pyridyl group.