%0 Journal Article %1 Sanyal.2007 %A Sanyal, Anasuya %A Chatterjee, Sudipta %A Castineiras, Alfonso %A Sarkar, Biprajit %A Singh, Priti %A Fiedler, Jan %A Zalis, Stanislav %A Kaim, Wolfgang %A Goswami, Sreebrata. %D 2007 %J Inorganic Chemistry %K 6 Group arylamidophenylazopyridine crystal diradical diradical;Group diradical;electronic electrochem metal prepn redox singlet structure %N 21 %P 8584--8593 %R 10.1021/ic700584x %T Singlet Diradical Complexes of Chromium, Molybdenum, and Tungsten with Azo Anion Radical Ligands from M(CO)6 Precursors %V 46 %X The homoleptic diamagnetic complexes M(mer-L)2, M = Cr, Mo, W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO)6 with the tridentate ligands 2-(2-N-arylamino)phenylazopyridine (HL = NH4C5N:NC6H4N(H)C6H4(H) (HLa) or NH4C5N:NC6H4N(H)C6H4Me (HLb)) in refluxing n-octane. In the case of M = Mo, dinuclear Mo(L)(pap)2(m-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction anal. for Cr(Lb)2 (1b), Mo(La)2 (2a), and W(La)2 (4a) reveals considerably distorted octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyl-N and anilido N atoms. Whereas the Nazo-M-Nazo angle is larger than 170°, the other two trans angles are smaller, at $\sim$155° (M = Cr, 1b) or 146° (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by \textgreater0.08 \AA than those to the anilido or azo N atoms, reflecting neg. charge on the latter. The N-N bond distances vary between 1.339(2) \AA for 1b and 1.373(3) \AA for 4a, clearly indicating the azo radical anion oxidn. state. Considering the addnl. neg. charge on anilido-N, the mononuclear complexes are thus formulated as MIV(L.bul.2-)2. The diamagnetism of the complexes as shown by magnetic susceptibility and 1H NMR expts. is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The exptl. structures are well reproduced by d. functional theory calcns., which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) \AA for La and 1.340(9) \AA for pap is also formulated as an azo anion radical-contg. Mo(IV) species, i.e., MoIV(L.bul.2-)(pap.bul.-)2(m-O). All compds. can be reversibly reduced; the Cr complexes 1a,b are also reversibly oxidized in two steps. ESR spectroscopy indicates metal-centered spin for 1a+ and 1a- and g $\approx$ 2 signals for 2a-, 3a+, 3a-, and 4a-. Spectroelectrochem. in the UV-visible-NIR region showed small changes for the redn. of 2a, 3a, and 4a but extensive spectral changes for the redn. and oxidn. of 1a. on SciFinder(R)

@article{Sanyal.2007, abstract = {The homoleptic diamagnetic complexes M(mer-L)2, M = Cr, Mo, W (1a,b, 2a,b, and 4a,b), were obtained by reacting the hexacarbonyls M(CO)6 with the tridentate ligands 2-[(2-N-arylamino)phenylazo]pyridine (HL = NH4C5N:NC6H4N(H)C6H4(H) (HLa) or NH4C5N:NC6H4N(H)C6H4Me (HLb)) in refluxing n-octane. In the case of M = Mo, dinuclear [Mo(L)(pap)]2(\textgreek{m}-O) (3a,b) (pap = 2-(phenylazo)pyridine), were obtained as second products in moist solvent. X-ray diffraction anal. for Cr(Lb)2 (1b), Mo(La)2 (2a), and W(La)2 (4a) reveals considerably distorted octahedral structures with trans-positioned azo-N atoms and cis-positioned 2-pyridyl-N and anilido N atoms. Whereas the Nazo-M-Nazo angle is larger than 170°, the other two trans angles are smaller, at $\sim$155° (M = Cr, 1b) or 146° (M = Mo, W; 2a, 4a), due to the overarching bite of the mer-tridentate ligands. The bonds from M to the neutral 2-pyridyl-N atoms are distinctly longer by {\textgreater}0.08 {\AA} than those to the anilido or azo N atoms, reflecting neg. charge on the latter. The N-N bond distances vary between 1.339(2) {\AA} for 1b and 1.373(3) {\AA} for 4a, clearly indicating the azo radical anion oxidn. state. Considering the addnl. neg. charge on anilido-N, the mononuclear complexes are thus formulated as MIV(L.bul.2-)2. The diamagnetism of the complexes as shown by magnetic susceptibility and 1H NMR expts. is believed to result from spin-spin coupling between the trans-positioned azo radical functions, resulting in a singlet diradical situation. The exptl. structures are well reproduced by d. functional theory calcns., which also support the overall electronic structure indicated. The dinuclear 3a with N-N distances of 1.348(10) {\AA} for La and 1.340(9) {\AA} for pap is also formulated as an azo anion radical-contg. Mo(IV) species, i.e., [MoIV(L.bul.2-)(pap.bul.-)]2(\textgreek{m}-O). All compds. can be reversibly reduced; the Cr complexes 1a,b are also reversibly oxidized in two steps. ESR spectroscopy indicates metal-centered spin for 1a+ and 1a- and g $\approx$ 2 signals for 2a-, 3a+, 3a-, and 4a-. Spectroelectrochem. in the UV-visible-NIR region showed small changes for the redn. of 2a, 3a, and 4a but extensive spectral changes for the redn. and oxidn. of 1a. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Sanyal, Anasuya and Chatterjee, Sudipta and Castineiras, Alfonso and Sarkar, Biprajit and Singh, Priti and Fiedler, Jan and Zalis, Stanislav and Kaim, Wolfgang and Goswami, Sreebrata.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/26c562fff7aafd3326ae925336280fe71/huebleriac}, doi = {10.1021/ic700584x}, interhash = {412e0b435c810a4b3f4b91984d70c292}, intrahash = {6c562fff7aafd3326ae925336280fe71}, issn = {0020-1669}, journal = {Inorganic Chemistry}, keywords = {6 Group arylamidophenylazopyridine crystal diradical diradical;Group diradical;electronic electrochem metal prepn redox singlet structure}, number = 21, pages = {8584--8593}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {Singlet Diradical Complexes of Chromium, Molybdenum, and Tungsten with Azo Anion Radical Ligands from M(CO)6 Precursors}, volume = 46, year = 2007 }