Metal-metal interaction in ligand-bridged dimolybdenum(0,0) and -(I,0) complexes with very small frontier orbital gaps: Electrochemistry and spectroscopic properties of three neighboring oxidation states
Complexes (m-L)[Mo(CO)2(PBu3)2]2 with cis-carbonyl ligands and sym. bridging bis(a-diimine) chelate ligands L = 2,2'-bipyrimidine (bpym) and 2,5-bis(2-pyridyl)pyrazine (2,5-bppz) were synthesized and studied in different oxidn. states by cyclic voltammetry, 1H NMR, EPR, IR and UV-visible-NIR absorption spectroscopy. The combination of two very electron rich d6 metal centers with one p accepting bridging ligand results in rather small HOMO-LUMO energy gaps, as evident from differences of $\sim$1 V between the potentials for reversible oxidn. and redn. and from intense charge transfer absorptions at $\sim$1 eV, i.e. in the near-IR (NIR) region. Whereas the shifts of the carbonyl vibrational bands are about equal for the redn. (low-energy shift) and the oxidn. (high-energy shift) of the more stable bpym complex, the EPR results reveal occupation of the a-diimine p* orbitals in the anionic forms and an Mo(I)/Mo(0) mixed-valent state with a comproportionation const. Kc \textgreater108 for (bpym)[Mo(CO)2(PBu3)2]2+. Electronic transitions obsd. by UV-visible-IR spectroelectrochem. confirm these assignments of the redox orbitals; the max. of the weak metal-to-metal charge transfer band of the mixed-valent complex (bpym)[Mo(CO)2(PBu3)2]2+ was found at 3700 nm (2700 cm-1). [on SciFinder(R)]
%0 Journal Article
%1 Kaim.1995
%A Kaim, Wolfgang
%A Bruns, Wolfgang
%A Kohlmann, Stephan
%A Krejcik, Michael.
%D 1995
%J Inorganica Chimica Acta
%K bipyrimidine bispyridyl bispyridylpyrazine bispyridylpyrazine;ESR bispyridylpyrazine;molybdenum carbonyl complex;electrochem complex;pyrazine complex;spectroelectrochem comproportionation diimine dinuclear molybdenum
%N 1-2
%P 143--151
%R 10.1016/0020-1693(94)04239-R
%T Metal-metal interaction in ligand-bridged dimolybdenum(0,0) and -(I,0) complexes with very small frontier orbital gaps: Electrochemistry and spectroscopic properties of three neighboring oxidation states
%V 229
%X Complexes (m-L)[Mo(CO)2(PBu3)2]2 with cis-carbonyl ligands and sym. bridging bis(a-diimine) chelate ligands L = 2,2'-bipyrimidine (bpym) and 2,5-bis(2-pyridyl)pyrazine (2,5-bppz) were synthesized and studied in different oxidn. states by cyclic voltammetry, 1H NMR, EPR, IR and UV-visible-NIR absorption spectroscopy. The combination of two very electron rich d6 metal centers with one p accepting bridging ligand results in rather small HOMO-LUMO energy gaps, as evident from differences of $\sim$1 V between the potentials for reversible oxidn. and redn. and from intense charge transfer absorptions at $\sim$1 eV, i.e. in the near-IR (NIR) region. Whereas the shifts of the carbonyl vibrational bands are about equal for the redn. (low-energy shift) and the oxidn. (high-energy shift) of the more stable bpym complex, the EPR results reveal occupation of the a-diimine p* orbitals in the anionic forms and an Mo(I)/Mo(0) mixed-valent state with a comproportionation const. Kc \textgreater108 for (bpym)[Mo(CO)2(PBu3)2]2+. Electronic transitions obsd. by UV-visible-IR spectroelectrochem. confirm these assignments of the redox orbitals; the max. of the weak metal-to-metal charge transfer band of the mixed-valent complex (bpym)[Mo(CO)2(PBu3)2]2+ was found at 3700 nm (2700 cm-1). [on SciFinder(R)]
@article{Kaim.1995,
abstract = {Complexes (\textgreek{m}-L)[Mo(CO)2(PBu3)2]2 with cis-carbonyl ligands and sym. bridging bis(\textgreek{a}-diimine) chelate ligands L = 2,2'-bipyrimidine (bpym) and 2,5-bis(2-pyridyl)pyrazine (2,5-bppz) were synthesized and studied in different oxidn. states by cyclic voltammetry, 1H NMR, EPR, IR and UV-visible-NIR absorption spectroscopy. The combination of two very electron rich d6 metal centers with one \textgreek{p} accepting bridging ligand results in rather small HOMO-LUMO energy gaps, as evident from differences of $\sim$1 V between the potentials for reversible oxidn. and redn. and from intense charge transfer absorptions at $\sim$1 eV, i.e. in the near-IR (NIR) region. Whereas the shifts of the carbonyl vibrational bands are about equal for the redn. (low-energy shift) and the oxidn. (high-energy shift) of the more stable bpym complex, the EPR results reveal occupation of the \textgreek{a}-diimine \textgreek{p}* orbitals in the anionic forms and an Mo(I)/Mo(0) mixed-valent state with a comproportionation const. Kc {\textgreater}108 for {(bpym)[Mo(CO)2(PBu3)2]2}+. Electronic transitions obsd. by UV-visible-IR spectroelectrochem. confirm these assignments of the redox orbitals; the max. of the weak metal-to-metal charge transfer band of the mixed-valent complex {(bpym)[Mo(CO)2(PBu3)2]2}+ was found at 3700 nm (2700 cm-1). [on SciFinder(R)]},
added-at = {2022-06-15T11:26:56.000+0200},
author = {Kaim, Wolfgang and Bruns, Wolfgang and Kohlmann, Stephan and Krejcik, Michael.},
biburl = {https://puma.ub.uni-stuttgart.de/bibtex/2b6310375385b612202c6b42c577e6e8f/huebleriac},
doi = {10.1016/0020-1693(94)04239-R},
interhash = {4d182c48dec9248737697061fc6e6bed},
intrahash = {b6310375385b612202c6b42c577e6e8f},
issn = {0020-1693},
journal = {Inorganica Chimica Acta},
keywords = {bipyrimidine bispyridyl bispyridylpyrazine bispyridylpyrazine;ESR bispyridylpyrazine;molybdenum carbonyl complex;electrochem complex;pyrazine complex;spectroelectrochem comproportionation diimine dinuclear molybdenum},
number = {1-2},
pages = {143--151},
timestamp = {2022-06-15T09:26:56.000+0200},
title = {Metal-metal interaction in ligand-bridged dimolybdenum(0,0) and -(I,0) complexes with very small frontier orbital gaps: Electrochemistry and spectroscopic properties of three neighboring oxidation states},
volume = 229,
year = 1995
}
