title: Synthesis and characterisation of dimeric eight-coordinate lanthanide(III) complexes of a macrocyclic tribenzylphosphinate ligand.
abstract: The macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7-triyl(methylenebenzyl-phosphinic acid) H3L3, has been prepared and its complexes with Eu, Gd and Tb(III) studied by NMR, relaxometry, luminescence and single crystal X-ray crystallography. In solution and in the crystal, the complexes have eight-coordinate metal centres with bridging phosphinate groups linking the two twisted square antiprismatic coordination polyhedra. A single stereoisomer crystallises from solution with an RRR and SSS configuration at the P centres in each sub-unit. The relaxivity of [GdL3]2 is low (1.9 mM-1 s-1, 298 K, 20 MHz), consistent with the absence of any proximate water molecules. The terbium dimer possesses a relatively long excited state lifetime (2.47 ms, 298 K).
authors.affiliation: Department of Chemistry, Durham University, South Road, Durham, UK DH1 3LE.
authors.forename: Kanthi
authors.initials: K
authors.lastname: Senanayake
authors.forename: Amber L
authors.initials: AL
authors.lastname: Thompson
authors.forename: Judith A K
authors.initials: JA
authors.lastname: Howard
authors.forename: Mauro
authors.initials: M
authors.lastname: Botta
authors.forename: David
authors.initials: D
authors.lastname: Parker