Spin states of the cobalt(II) complex with bis(pyrazol-3-yl)pyridine and pH-sensitive functional groups and its deprotonated derivatives

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Abstract

The reaction of 2,6-bis(pyrazol-3-yl)pyridine H2L bearing pH-sensitive imino groups with cobalt perchlorate hexahydrate followed by the addition of 1,8-diazabicyclo[5.4.0]undec-7-ene affords the cobalt(II) complex [Co(H2L)2](ClO4)2 (I) and its doubly deprotonated analog [Co(HL)2]0 (II). The compounds are characterized by NMR spectroscopy, mass spectrometry, and XRD. The influence of the deprotonation of ligand H2L with a chosen base on the spin state of the cobalt(II) ion in a solution is studied by in situ NMR spectroscopy. Complex I is shown to retain its high-spin state in the whole temperature range accessible in deuterated methanol (200–325 K) both before and after the deprotonation of all pH-sensitive imino groups. However, the doubly deprotonated form of complex I (complex II–2MeOH) exists in the crystal (CIF file CCDC no. 2351546) in the low-spin state, which is the first example of the pH-induced stabilization of this state for the cobalt(II) complexes with 2,6-bis(pyrazol-3-yl)pyridines.

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About the authors

E. S. Safiullina

Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences; Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences

Author for correspondence.
Email: fluflucat@gmail.com
Russian Federation, Moscow; Moscow

I. A. Nikovskii

Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences

Email: fluflucat@gmail.com
Russian Federation, Moscow

A. A. Dan’shina

Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences; Moscow Institute of Physics and Technology (National Research University)

Email: fluflucat@gmail.com
Russian Federation, Moscow; Dolgoprudnyi, Moscow oblast

Yu. V. Nelyubina

Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences

Email: fluflucat@gmail.com
Russian Federation, Moscow

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Supplementary files

Supplementary Files
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2. Scheme 1. Scheme for the synthesis of the [Co(H2L)2](ClO4)2 complex (I).

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3. Fig. 1. NMR spectra 1H of complex I obtained by mixing the ligand H2L with cobalt perchlorate in deuteromethanol, at different temperatures.

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4. Scheme 2. Proposed scheme for deprotonation of the [Co(H2L)2](ClO4)2 (I) complex under the action of DBU (counterions omitted).

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5. Fig. 2. 1H NMR spectra of complex I obtained by mixing the H2L ligand with cobalt perchlorate in deuteromethanol before (a) and after adding 2 (b), 4 (c), and 6 (d) equiv. of base.

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6. Fig. 3. General view of complex II in the crystal of [Co(HL)2]0 2MeOH. Hydrogen atoms, except for those belonging to the imino groups of the ligands and the hydroxy groups of the solvate molecules of methanol, are not shown, and the remaining atoms are presented as thermal vibration ellipsoids (p = 30%). Numbering is given only for the metal ion and heteroatoms.

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7. Fig. 4. 1H NMR spectra of the in situ deprotonation product of complex I obtained by mixing the H2L ligand with cobalt perchlorate in deuteromethanol, 4 equiv. base at different temperatures.

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8. Fig. 5. Dependences of paramagnetic chemical shifts on the reciprocal temperature for complex I obtained by mixing the H2L ligand with cobalt perchlorate in deuteromethanol (a) and the product of its in situ deprotonation of 4 equiv. base (b). The lines in the figure are linear approximations of the obtained dependences. The signal designations correspond to the designations in Fig. 1: 3-Py (■), Pz (●), t-Bu (▲), 4-Py (▼).

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