BINUCLEAR STRUCTURE IN THE AMMONIUM SALT OF GADOLINIUM(III) DIETHYLENETRIAMINEPENTAACETATE, (NH4)(4)[GD-2(DTPA)(2)]CENTER-DOT-6H(2)O

A single crystal X-ray analysis of the ammonium salt of Gd3+ diethylen etriaminepentaacetate has shown that the compound has a binuclear stru cture in contrast to the corresponding sodium salt that has a mononucl ear structure. Five oxygen atoms and three nitrogen atoms from a ligan d molecule construct a distorted square antiprism around a Gd3+ ion. O ne of the square planes is capped by an oxygen atom from the adjacent metal chelate molecule, resulting in the formation of a binuclear meta l chelate. The coordination polyhedron including this oxygen atom is d escribed as a tricapped trigonal prism. The binuclear structure is the result of well-developed hydrogen bonds that involve the ammonium ion s.