Mono‐, Di‐ and Polymeric Calcium and Gadolinium Complexes of the Tripodal Ligand 2,2′,2′′‐Nitrilotribenzoic Acid

Abstract

Abstract Three novel carboxylate‐bridged complexes incorporating the tripodal N,O ligand 2,2′,2′′‐nitrilotribenzoic acid H 3 L of formula [Ca II (H 2 L)(OH 2 ) 4 ][(H 2 L)] · 4H 2 O ( 1 ), [Ca II (OH 2 ) 4 ]‐[Ca II (L)(OH 2 ) 2 ] 2 · 7H 2 O ( 2 ) and [Gd III (L)(OH 2 ) 3 ] 2 [Gd III (L)‐(OH 2 ) 4 ] 2 · 13H 2 O ( 3 ) were synthesized and characterized by X‐ray crystallography. In all three complexes, the ligand H 3 L binds to the metal centre only by its three carboxylate donors, leaving the bridgehead nitrogen atom nonbonding. The calcium( II ) ion in the monomeric complex 1 is distorted pentagonal‐bipyramidal coordinated, the +1 charge of the complex cation [Ca II (H 2 L)(OH 2 ) 4 ] + is balanced by an H 2 L – anion and both units are connected by hydrogen bonds. The polymeric compound 2 displays a one‐dimensional chain structure, in which two [Ca II (L)] 2– units form a dimeric structure and are connected by hydrated Ca II ions. 3 contains two different [Gd III (L)(OH 2 ) n ] dimers. In one of them the two Gd III ions are linked by two monoatomic carboxylate O‐bridges showing a short Gd ··· Gd distance of 3.99 Å. In the second, a syn ‐ anti carboxylate 1,3‐bridge with a longer Gd ··· Gd distance of 4.96 Å is observed. Magnetic measurements of 3 show paramagnetic behaviour with weak antiferromagnetic coupling. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)