%0 Journal Article
%A De Alwis, D. Chanaka L.
%A Schultz, Franklin A.
%D 2003
%T Metal−Bis[poly(pyrazolyl)borate] Complexes. Electrochemical, Magnetic,
and Spectroscopic Properties and Coupled Electron-Transfer and
Spin-Exchange Reactions
%U https://acs.figshare.com/articles/journal_contribution/Metal_Bis_poly_pyrazolyl_borate_Complexes_Electrochemical_Magnetic_and_Spectroscopic_Properties_and_Coupled_Electron-Transfer_and_Spin-Exchange_Reactions/3611784
%R 10.1021/ic034077a.s004
%2 https://ndownloader.figshare.com/files/5700339
%K cyclic voltammetric peak
%K potential
%K Slow electron transfer
%K Mn
%K MN
%K pzTp
%K Ligand field strengths
%K Co
%K spectroscopic properties
%K Tp
%K complex
%X Electrochemical, magnetic, and spectroscopic properties are reported for homoleptic divalent (M = Mn, Fe, Co, Ni,
Ru) and trivalent (M = Cr, Mn, Fe, Co) metal−bis[poly(pyrazolyl)borate] complexes, [M(pzb)2]+/0, where pzb- =
hydrotris(pyrazolyl)borate (Tp), hydrotris(3,5-dimethylpyrazolyl)borate (Tp*), or tetrakis(pyrazolyl)borate (pzTp). Ligand
field strengths in metal−pzb complexes increase as Tp* < Tp < pzTp, which reflects the importance of steric rather
than electronic effects on spectroscopic properties. However, metal-centered redox potentials become more negative
as pzTp < Tp < Tp*, which follows the electron-donating ability of the ligands. Co(III)/Co(II) and Mn(III)/Mn(II)
electrode reactions are accompanied by a change in metal atom spin-state; i.e., (S = 0) [Co(pzb)2]+ + e- ⇆ (S
= 3/2) [Co(pzb)2] and (S = 1) [Mn(pzb)2]+ + e- ⇆ (S = 5/2) [Mn(pzb)2]. Apparent heterogeneous electron-transfer
rate constants derived from sweep-rate dependent cyclic voltammetric peak potential separations in 1,2-dichloroethane
are small and decrease as pzTp > Tp > Tp* for the Co(III)/Co(II) couples. Slow electron transfer is characteristic
of coupled electron transfer and spin exchange. [M(Tp)2]+/0 redox potentials relative to values for other homoleptic
MN63+/2+ couples change as M varies from Cr to Ni. For early members of the series, [M(Tp)2]+/0 potentials nearly
equal those of complexes with aliphatic N-donor ligands (e.g., triazacyclononane, sarcophagine). However, [M(Tp)2]+/0
potentials approach those of [M(bpy)3]3+/2+ for later members of the series. The variation suggests a change in the
nature of the metal−pzb interaction upon crossing the first transition row.
%I ACS Publications