TY - JOUR
T1 - Ligand exchange and spin state equilibria of Fe II(N4Py) and related complexes in aqueous media
AU - Draksharapu, Apparao
AU - Li, Qian
AU - Logtenberg, Hella
AU - Van Den Berg, Tieme A.
AU - Meetsma, Auke
AU - Killeen, J. Scott
AU - Feringa, Ben L.
AU - Hage, Ronald
AU - Roelfes, Gerard
AU - Browne, Wesley R.
PY - 2012/1/16
Y1 - 2012/1/16
N2 - We report the characterization and solution chemistry of a series of Fe II complexes based on the pentadentate ligands N4Py (1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine), MeN4Py (1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)ethanamine), and the tetradentate ligand Bn-N3Py (N-benzyl-1,1-di(pyridin-2-yl)-N-(pyridin-2- ylmethyl)methanamine) ligands, i.e., [Fe(N4Py)(CH 3CN)](ClO 4) 2 (1), [Fe(MeN4Py)(CH 3CN)](ClO 4) 2 (2), and [Fe(Bn-N3Py)(CH 3CN) 2](ClO 4) 2 (3), respectively. Complexes 2 and 3 are characterized by X-ray crystallography, which indicates that they are low-spin Fe II complexes in the solid state. The solution properties of 1-3 are investigated using 1H NMR, UV/vis absorption, and resonance Raman spectroscopies, cyclic voltammetry, and ESI-MS. These data confirm that in acetonitrile the complexes retain their solid-state structure, but in water immediate ligand exchange of the CH 3CN ligand(s) for hydroxide or aqua ligands occurs with full dissociation of the polypyridyl ligand at low (<3) and high (>9) pH. pH jumping experiments confirm that over at least several minutes the ligand dissociation observed is fully reversible for complexes 1 and 2. In the pH range between 5 and 8, complexes 1 and 2 show an equilibrium between two different species. Furthermore, the aquated complexes show a spin equilibrium between low- and high-spin states with the equilibrium favoring the high-spin state for 1 but favoring the low-spin state for 2. Complex 3 forms only one species over the pH range 4-8, outside of which ligand dissociation occurs. The speciation analysis and the observation of an equilibrium between spin states in aqueous solution is proposed to be the origin of the effectiveness of complex 1 in cleaving DNA in water with 3O 2 as terminal oxidant.
AB - We report the characterization and solution chemistry of a series of Fe II complexes based on the pentadentate ligands N4Py (1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine), MeN4Py (1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)ethanamine), and the tetradentate ligand Bn-N3Py (N-benzyl-1,1-di(pyridin-2-yl)-N-(pyridin-2- ylmethyl)methanamine) ligands, i.e., [Fe(N4Py)(CH 3CN)](ClO 4) 2 (1), [Fe(MeN4Py)(CH 3CN)](ClO 4) 2 (2), and [Fe(Bn-N3Py)(CH 3CN) 2](ClO 4) 2 (3), respectively. Complexes 2 and 3 are characterized by X-ray crystallography, which indicates that they are low-spin Fe II complexes in the solid state. The solution properties of 1-3 are investigated using 1H NMR, UV/vis absorption, and resonance Raman spectroscopies, cyclic voltammetry, and ESI-MS. These data confirm that in acetonitrile the complexes retain their solid-state structure, but in water immediate ligand exchange of the CH 3CN ligand(s) for hydroxide or aqua ligands occurs with full dissociation of the polypyridyl ligand at low (<3) and high (>9) pH. pH jumping experiments confirm that over at least several minutes the ligand dissociation observed is fully reversible for complexes 1 and 2. In the pH range between 5 and 8, complexes 1 and 2 show an equilibrium between two different species. Furthermore, the aquated complexes show a spin equilibrium between low- and high-spin states with the equilibrium favoring the high-spin state for 1 but favoring the low-spin state for 2. Complex 3 forms only one species over the pH range 4-8, outside of which ligand dissociation occurs. The speciation analysis and the observation of an equilibrium between spin states in aqueous solution is proposed to be the origin of the effectiveness of complex 1 in cleaving DNA in water with 3O 2 as terminal oxidant.
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U2 - 10.1021/ic201879b
DO - 10.1021/ic201879b
M3 - Article
C2 - 22220629
AN - SCOPUS:84862958951
SN - 0020-1669
VL - 51
SP - 900
EP - 913
JO - Inorganic chemistry
JF - Inorganic chemistry
IS - 2
ER -