Synthesis and characterization of two stable paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands and of a chromium(III) complex with a ONO donor ligand

Koley, Manjuri K. ; Sivasubramanian, Seshadri C. ; Varghese, Babu ; Manoharan, Periakaruppan T. ; Koley, Aditya P. (2008) Synthesis and characterization of two stable paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands and of a chromium(III) complex with a ONO donor ligand Inorganica Chimica Acta, 361 (5). pp. 1485-1495. ISSN 0020-1693

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S00201...

Related URL: http://dx.doi.org/10.1016/j.ica.2007.09.033

Abstract

Two novel paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands containing extended p-system have been synthesized while only a paramagnetic octahedral chromium(III) complex is obtained when a related dianionic tridentate ONO donor ligand is used under similar conditions. These bischelate complexes [Cr(abtsal)2] (1) (abtsalH2 is the Schiff base of o-aminobenzenethiol and salicylaldehyde), [Cr(4-PhTSCsal)2] · H2O (2) (4-PhTSCsalH2 is the Schiff base of 4-phenylthiosemicarbazide and salicylaldehyde) and K[Cr(sap)2]· H2O (3) (sapH2 is the tridentate Schiff base of salicylaldehyde and o-aminophenol) are characterized by elemental analyses, magnetic moment measurements, IR, UV-Vis and EPR spectroscopic studies. Compound 3 has been structurally characterized by X-ray crystallography. Measured room temperature (RT) magnetic moment values are 2.98 BM for 1 and 2.83 BM for 2 indicating a d2 system with a triplet ground state in both the cases. On the other hand, the magnetic moment value for 3 is found to be 3.74 BM at RT and is consistent with the presence of three unpaired electrons for a d3 Cr(III) ion. The magnetic moment values rule out the large spin-orbit coupling which is substantiated by the presence of RT EPR signals. Compounds 1 and 2 exhibit very similar powder EPR spectra at RT and LNT, which show the allowed transition ΔMs = ±1 (g = 2.004 for both 1 and 2) as well as the "forbidden" half-field transition (ΔMs = ±2) at g = 4.105 for 1 and g = 4.318 for 2, respectively. The X-band LNT frozen glass EPR spectrum of 1 in DMF shows the presence of zero-field split rhombic symmetry character, and results in the parameters g 2.0, D = 740 G, and E = 260 G. It suggests that the intensity ofΔMs = ±2 forbidden transition is large due to the large D value. The X-band frozen glass EPR spectrum of compound 3 in DMF is found to be very similar to that reported for trans-[Cr(py)4F2]+ in DMF-H2O-MeOH glass. The large difference (~700 mV) in the reduction potential for the two octahedral complexes 1 (-1.40 V) and 3 (-0.70 V) is attributed to the difference in their metal ion oxidation states.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Chromium(IV) and Chromium(III) Complexes; SNO and ONO Donors; EPR and Electronic Spectra; X-ray Structure; Electrochemistry; Cyclic Voltammetry
ID Code:19894
Deposited On:22 Nov 2010 11:42
Last Modified:06 Jun 2011 12:03

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