Synthesis, characterization and solution 113Cd NMR analysis of Cd(II) 1,4,7,10,13-pentaazacyclopentadecane complexes

Abstract

Two new cadmium(II) complexes of the macrocyclic ligand, 1,4,7,10,13-pentaazacyclopentadecane 5, have been prepared and characterized. The crystal structure of dichlorocadmium(II) complex 3 was determined and reveals that the Cd(II) is coordinated in a pentagonal bipyramidal array of the five nitrogens of the macrocyclic ring and capped by two trans-chloro ligands. Crystal data for Cd(C 10H 25N 5)Cl 2–0.5H 2O are as follows: monoclinic at 20 °C, space group C2/c−C 6 2h (No. 15) with a =22.165(5) Å, b =11.439(3) Å, c =14.6788(4) Å, β=118.75(2)°, V=3262(2) Å 3 and Z=8 [ d calcd=1.660 g cm −3; μ a(Mo K α)=1.66 mm −1]. Solution 1H, 13C and 113Cd NMR studies of complex 3 suggest that in non-polar solvents, such as CDCl 3, the seven-coordinate structure is maintained, while in aqueous media dissociation of one axial chloride ligand affords a macrocyclic ligand-folded six-coordinate species. This is analogous to the dichloromanganese(II) complex 1. Folding of the pentaazamacrocyclic ligand 5 is confirmed as a relevant structural motif for this series of complexes by the X-ray structure determination of the bis(nitrate) derivative. Complex 4 [Cd(C 10H 25N 5)NO 3]NO 3 reveals a six-coordinate structure with a folded conformation of the macrocyclic ligand. Crystal data for [Cd(C 10H 25N 5)NO 3]NO 3 is as follows: orthorhombic at 20 °C, space group P2 12 12 1−D 4 2 (No. 19) with a =9.627(2) Å, b =12.858(2) Å, c =14.003(2) Å, V=1733.3(6) Å 3 and Z=4 [ d calcd=1.731 g cm −3; μ a(Mo K α)=1.30 mm −1]. Solution 1H, 13C and 113Cd NMR studies of complex 4 suggest six-coordinate structures in both CDCl 3 and D 2O, again with the macrocyclic ligand in a folded conformation. Again, this is entirely analogous to the Mn(II) bis(nitrate) complex 2. 113Cd NMR shifts are consistent with literature predictions for the types and numbers of coordinating ligands in complexes 3 and 4 in both NMR solvents.