Crystal structures, magnetic properties and DFT study of cobalt(II) azido complexes with the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent
Graphical abstract
Crystal structures of mono- and dinuclear cobalt(II) azido complexes with the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent. DFT-BS explanation of ferromagnetic exchange coupling in dinuclear Co(II) complex. Magnetic properties of mononuclear Co(II) complex.
Introduction
Investigation of azido bridged polynuclear d-metal complexes is an attractive field of research due to their interesting structural, spectroscopic and magnetic properties [1]. The azido ligand is one of the most extensively used pseudohalide building block for preparation of mono- [2] and polynuclear d-metals coordination compounds of different dimensionalities [3]. It can acts as monodentate [2] or exhibits many bridging coordination modes: single and double μ1,3-N3 (end-to-end, EE) and μ1,1-N3 (end-on, EO), μ1,1,3-N3, μ1,1,1-N3, μ1,1,1,1-N3, μ1,1,3,3-N3, and μ1,1,1,3,3,3-N3 [1](a), [4]. A relatively large number of dinuclear azido bridged Cu(II), Ni(II) and Mn(II) [3], [5] complexes have been reported, while the end-on azido bridged Co(II) complexes are rare [6], probably due to the synthetic problems to obtain good quality single crystals and oxidation to Co(III) complexes. DFT calculations on EO and EE azido bridged dinuclear transition metal complexes provide good predictions of their magnetic properties. Also, these systems are excellent examples for theoretical analysis of exchange coupling [7]. Low spin Co(II) complexes are very rare. In contrast to octahedral Co(II) complexes, the number of the reported square-planar and five coordinated Co(II) complexes is higher. Very strong-field ligands are required to undergo spin pairing in Co(II) complexes. The Jahn-Teller effect favorizes the loss of some ligand to give four- or five- rather than six-coordinate complexes [8], [9]. Complexes of d-metals with the condensation product of 2-quinolinecarboxaldehyde and trimethylammonium acetohydrazide chloride (Girard’s T reagent) (HLCl) and pseudohalides have recently been the subject of study of our research group [10], [11]. The ligand (HLCl) is a quaternary ammonium salt, which acts as a potentially tridentate ligand and can be coordinated via quinoline nitrogen, azomethine nitrogen and carbonyl oxygen atoms. Also, this ligand exhibits keto-enol tautomerism and can coordinate metal ions in non-deprotonated positively charged form or deprotonated formally neutral zwitter-ionic form. Recently, we reported the synthesis and characterization of dinuclear end-on azido bridged Ni(II) complex [Ni2L2(μ-1,1-N3)2(N3)2] [10] and mononuclear azido Zn(II) complex [ZnL(N3)2] [10] with this ligand. Here, we present synthesis, structural characterization and magnetic properties of mononuclear azido Co(II) complex [CoHL(N3)3] (1) and dinuclear end-on azido bridged Co(II) complex [Co2L2(μ-1,1-N3)2(N3)2] (2) with the same ligand.
Section snippets
Materials and methods
2-Quinolinecarboxaldehyde (97%) and Girard’s T reagent (99%) were obtained from Aldrich. IR spectra were recorded on a Nicolet 6700 FT-IR spectrometer using the ATR technique in the region 4000–400 cm−1 (s-strong, m-medium, w-weak). Elemental analyses (C, H, and N) were performed by standard micro-methods using the ELEMENTARVario ELIII C.H.N.S.O analyzer. The temperature dependence of magnetic susceptibility was measured on the powder sample using a Quantum Design MPMS-XL-5 SQUID magnetometer,
Synthesis
The ligand (E)-N,N,N-trimethyl-2-oxo-2-(2-(quinolin-2-ylmethylene)hydrazinyl)ethan-1-aminium chloride (HLCl), was obtained in the condensation reaction of 2-quinolinecarboxaldehyde and Girard’s T reagent using the previously described method, Scheme 1 [10]. Reaction of the ligand HLCl with Co(BF4)2·6H2O and NaN3 in molar ratio 1:1:4 in methanol/acetonitrile mixture results in formation of mononuclear octahedral azido Co(II) complex (1) [CoHL(N3)3], as a main product, and a dinuclear double
Conclusions
Complex 1 was obtained as a main product in the reaction of the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent (HLCl) with Co(BF4)2·6H2O and NaN3 in molar ratio 1:1:4 in methanol/acetonitrile mixture together with a dinuclear double end-on azido bridged Co(II) complex (2). The octahedral Co(II) complex (1) with three azido ligands in meridional alignment favors low-spin configuration and the magnetic moment very close to the spin-only value. Octahedral surrounding
Acknowledgements
This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grant OI 172055) and Slovenian Research Agency (P-0175). We thank the EN-FIST Centre of Excellence, Ljubljana, Slovenia, for use of the SuperNova diffractometer. Part of this work was supported by COST Action CM1305 “Explicit Control Over Spin-states in Technology and Biochemistry (ECOSTBio)” and was done during STSM, reference number COST-STSM-CM1305-37566.
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