ChemInform Abstract: 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 10 H 25 N 5 )Cl 2 –0.5H 2 O are as follows: monoclinic at 20 °C, space group C2/c−C 6 2h (No. 15) with a =22.165(5) A, b =11.439(3) A, c =14.6788(4) A, β =118.75(2)°, V =3262(2) A 3 and Z =8 [ d calcd =1.660 g cm −3 ; μ a (Mo K α )=1.66 mm −1 ]. Solution 1 H, 13 C and 113 Cd 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 10 H 25 N 5 )NO 3 ]NO 3 reveals a six-coordinate structure with a folded conformation of the macrocyclic ligand. Crystal data for [Cd(C 10 H 25 N 5 )NO 3 ]NO 3 is as follows: orthorhombic at 20 °C, space group P2 1 2 1 2 1 −D 4 2 (No. 19) with a =9.627(2) A, b =12.858(2) A, c =14.003(2) A, V =1733.3(6) A 3 and Z =4 [ d calcd =1.731 g cm −3 ; μ a (Mo K α )=1.30 mm −1 ]. Solution 1 H, 13 C and 113 Cd NMR studies of complex 4 suggest six-coordinate structures in both CDCl 3 and D 2 O, again with the macrocyclic ligand in a folded conformation. Again, this is entirely analogous to the Mn(II) bis(nitrate) complex 2 . 113 Cd NMR shifts are consistent with literature predictions for the types and numbers of coordinating ligands in complexes 3 and 4 in both NMR solvents. Figure options Download full-size image Download as PowerPoint slide