Dinuclear, bishydrated Gd(super III) polyaminocarboxylates with a rigid xylene core display remarkable proton relaxivities

[Gd2(px(DTTA)(sub 2)(H2O)(sub 4)](super 2-) and [Gd2(mX(DTTA)(sub 2)0(H2O)(sub 4)](super 2-) the two nuclear dinuclear Gd(super III) complexes are synthesized based on a xylene core substituted with diethylenetriamine-N,N,N',N'-tetraacetate (DTTA) chelators in para or meta position. The increased molecular size as compared to monomeric compounds associated with the rigid xylene linker between the two Gd(super III) chelating subunits also contributes to an increased relaxivity.