Versatile Reactivity of Mn^II Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates

• Main Authors: Ruslan A. Polunin, Igor S. Evstifeev, Olivier Cador, Stéphane Golhen, Konstantin S. Gavrilenko, Anton S. Lytvynenko, Nikolay N. Efimov, Vadim V. Minin, Artem S. Bogomyakov, Lahcène Ouahab, Sergey V. Kolotilov, Mikhail A. Kiskin, Igor L. Eremenko
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Molecules
• Subjects: polynuclear complexes; manganese; pyridines; coordination polymers; porous materials; magnetic properties
• Online Access: https://www.mdpi.com/1420-3049/26/4/1021
• ISSN: 1420-3049

<b> </b>Reaction of 2,2′-bipyridine (2,2′-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)₂(EtOH)]_n led to the formation of binuclear complexes [Mn₂(Piv)₄L₂] (L = 2,2′-bipy (<b>1</b>), phen (<b>2</b>); Piv^- is the anion of pivalic acid). Oxidation of <b>1</b> or <b>2</b> by air oxygen resulted in the formation of tetranuclear Mn^II/III complexes [Mn₄O₂(Piv)₆L₂] (L = 2,2′-bipy (<b>3</b>), phen (<b>4</b>)). The hexanuclear complex [Mn₆(OH)₂(Piv)₁₀(pym)₄] (<b>5</b>) was formed in the reaction of [Mn(Piv)₂(EtOH)]_n with pyrimidine (pym), while oxidation of <b>5 </b>produced<b> </b>the coordination polymer [Mn₆O₂(Piv)₁₀(pym)₂]_n (<b>6</b>). Use of pyrazine (pz) instead of pyrimidine led to the 2D-coordination polymer [Mn₄(OH)(Piv)₇(µ₂-pz)₂]_n (<b>7</b>). Interaction of [Mn(Piv)₂(EtOH)]_n with FeCl₃ resulted in the formation of the hexanuclear complex [Mn^II₄Fe^III₂O₂(Piv)₁₀(MeCN)₂(HPiv)₂] (<b>8</b>). The reactions of [MnFe₂O(OAc)₆(H₂O)₃] with 4,4′-bipyridine (4,4′-bipy) or <i>trans</i>-1,2-(4-pyridyl)ethylene (bpe) led to the formation of 1D-polymers [MnFe₂O(OAc)₆L₂]_n·2<i>n</i>DMF, where L = 4,4′-bipy (<b>9</b>·2DMF), bpe (<b>10</b>·2DMF) and [MnFe₂O(OAc)₆(bpe)(DMF)]_n·3.5<i>n</i>DMF (<b>11</b>·3.5DMF). All complexes were characterized by single-crystal X-ray diffraction. Desolvation of <b>11</b>·3.5DMF led to a collapse of the porous crystal lattice that was confirmed by PXRD and N₂ sorption measurements, while alcohol adsorption led to porous structure restoration. Weak antiferromagnetic exchange was found in the case of binuclear Mn^II complexes (<i>J</i>_Mn-Mn = −1.03 cm⁻¹ for <b>1</b> and <b>2</b>). According to magnetic data analysis (<i>J</i>_Mn-Mn = −(2.69 ÷ 0.42) cm⁻¹) and DFT calculations (<i>J</i>_Mn-Mn = −(6.9 ÷ 0.9) cm⁻¹) weak antiferromagnetic coupling between Mn^II ions also occurred in the tetranuclear {Mn₄(OH)(Piv)₇} unit of the 2D polymer <b>7</b>. In contrast, strong antiferromagnetic coupling was found in oxo-bridged trinuclear fragment {MnFe₂O(OAc)₆} in <b>11</b>·3.5DMF (<i>J</i>_Fe-Fe = −57.8 cm⁻¹, <i>J</i>_Fe-Mn = −20.12 cm⁻¹).