Complex formation between polymers containing the 2, 2′-bipyridyl group and iron(II)

Abstract

Condensation polymers derived from the reaction of butane-1,4-diol and either the 4,4′- or 5,5′-di-acid derivatives of 2,2′-bipyridyl have been prepared. The formation of strongly coloured complexes between iron(II) and soluble portions of the products has been investigated. In the case of the polymer derived from the 5,5′-disubstituted bipyridyl the polymeric ligand appears to behave as a collection of independent ligand groups, but approximately one half of these groups are prevented from taking part in the formation of a ‘tris’ complex. The polymer derived from the 4,4′-disubstituted ligand behaves differently. The polymer chain develops meta to the ring–ring bond of the bipyridyl group. The difficulty of rotation of this bond produces two different types of bipyridyl repeat unit. One behaves as a ligand in the same way as the monomeric ligand, the other does not. Presumably these are fixed cis and trans configurations. The inflexibility of the polymer chain prevents the majority of the potential ligand groups from participating in the formation of a ‘tris’ complex, which formation involves only two polymer chains. Data are quoted for the stability constants relating to both polymers.