TY - JOUR
T1 - Trigonal Mn 3 and Co 3 clusters supported by weak-field ligands
T2 - A structural, spectroscopic, magnetic, and computational investigation into the correlation of molecular and electronic structure
AU - Fout, Alison R.
AU - Xiao, Dianne J.
AU - Zhao, Qinliang
AU - Harris, T. David
AU - King, Evan R.
AU - Eames, Emily V.
AU - Zheng, Shao Liang
AU - Betley, Theodore A.
PY - 2012/10/1
Y1 - 2012/10/1
N2 - Transamination of divalent transition metal starting materials (M 2(N(SiMe 3) 2) 4, M = Mn, Co) with hexadentate ligand platforms RLH 6 ( RLH 6 = MeC(CHNPh-o- NR) 3 where R = H, Ph, Mes (Mes = Mesityl)) or H,CyLH 6 = 1,3,5-C 6H 9(NHPh-o-NH) 3 with added pyridine or tertiary phosphine coligands afforded trinuclear complexes of the type (RL)Mn 3(py) 3 and ( RL)Co 3(PMe 2R′) 3 (R′ = Me, Ph). While the sterically less encumbered ligand varieties, HL or PhL, give rise to local square-pyramidal geometries at each of the bound metal atoms, with four anilides forming an equatorial plane and an exogenous pyridine or phosphine in the apical site, the mesityl-substituted ligand (MesL) engenders local tetrahedral coordination. Both the neutral Mn 3 and Co 3 clusters feature S = 1/2 ground states, as determined by direct current (dc) magnetometry, 1H NMR spectroscopy, and low-temperature electron paramagnetic resonance (EPR) spectroscopy. Within the Mn 3 clusters, the long internuclear Mn-Mn separations suggest minimal direct metal-metal orbital overlap. Accordingly, fits to variable-temperature magnetic susceptibility data reveal the presence of weak antiferromagnetic superexchange interactions through the bridging anilide ligands with exchange couplings ranging from J = -16.8 to -42 cm -1. Conversely, the short Co-Co interatomic distances suggest a significant degree of direct metal-metal orbital overlap, akin to the related Fe 3 clusters. With the Co 3 series, the S = 1/2 ground state can be attributed to population of a single molecular orbital manifold that arises from mixing of the metal- and o-phenylenediamide (OPDA) ligand-based frontier orbitals. Chemical oxidation of the neutral Co 3 clusters affords diamagnetic cationic clusters of the type [( RL)Co 3(PMe 2R) 3] +. Density functional theory (DFT) calculations on the neutral (S = 1/2) and cationic (S = 0) Co 3 clusters reveal that oxidation occurs at an orbital with contributions from both the Co 3 core and OPDA subunits. The predicted bond elongations within the ligand OPDA units are corroborated by the ligand bond perturbations observed by X-ray crystallography.
AB - Transamination of divalent transition metal starting materials (M 2(N(SiMe 3) 2) 4, M = Mn, Co) with hexadentate ligand platforms RLH 6 ( RLH 6 = MeC(CHNPh-o- NR) 3 where R = H, Ph, Mes (Mes = Mesityl)) or H,CyLH 6 = 1,3,5-C 6H 9(NHPh-o-NH) 3 with added pyridine or tertiary phosphine coligands afforded trinuclear complexes of the type (RL)Mn 3(py) 3 and ( RL)Co 3(PMe 2R′) 3 (R′ = Me, Ph). While the sterically less encumbered ligand varieties, HL or PhL, give rise to local square-pyramidal geometries at each of the bound metal atoms, with four anilides forming an equatorial plane and an exogenous pyridine or phosphine in the apical site, the mesityl-substituted ligand (MesL) engenders local tetrahedral coordination. Both the neutral Mn 3 and Co 3 clusters feature S = 1/2 ground states, as determined by direct current (dc) magnetometry, 1H NMR spectroscopy, and low-temperature electron paramagnetic resonance (EPR) spectroscopy. Within the Mn 3 clusters, the long internuclear Mn-Mn separations suggest minimal direct metal-metal orbital overlap. Accordingly, fits to variable-temperature magnetic susceptibility data reveal the presence of weak antiferromagnetic superexchange interactions through the bridging anilide ligands with exchange couplings ranging from J = -16.8 to -42 cm -1. Conversely, the short Co-Co interatomic distances suggest a significant degree of direct metal-metal orbital overlap, akin to the related Fe 3 clusters. With the Co 3 series, the S = 1/2 ground state can be attributed to population of a single molecular orbital manifold that arises from mixing of the metal- and o-phenylenediamide (OPDA) ligand-based frontier orbitals. Chemical oxidation of the neutral Co 3 clusters affords diamagnetic cationic clusters of the type [( RL)Co 3(PMe 2R) 3] +. Density functional theory (DFT) calculations on the neutral (S = 1/2) and cationic (S = 0) Co 3 clusters reveal that oxidation occurs at an orbital with contributions from both the Co 3 core and OPDA subunits. The predicted bond elongations within the ligand OPDA units are corroborated by the ligand bond perturbations observed by X-ray crystallography.
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U2 - 10.1021/ic301278m
DO - 10.1021/ic301278m
M3 - Article
C2 - 22991939
AN - SCOPUS:84868140173
SN - 0020-1669
VL - 51
SP - 10290
EP - 10299
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 19
ER -