Abstract
Two Mn(III)-based dimers, [Mn2(bpad)2(CH3O)4]n (1) and [Mn2(bpad)2(pa)2]n·2H2O (2) (Hbpad = N3-benzoylpyridine-2-carboxamidrazone, H2pa = phthalic acid), have been assembled from a tridentate Schiff-base chelator and various anionic coligands. Noteworthily, compound 1 could be identified as a reaction precursor to transform to 2 in the presence of phthalic acid, resulting in a rarely structural conversion process in which the bridges between intradimer Mn(III) ions alter from methanol oxygen atom with μ2-O mode in 1 (Mn Mn distance of 3.046 Å) to syn-anti carboxylate in 2 (Mn Mn distance of 4.043 Å), while the Mn(III) centers retain hexa-coordinated geometries with independently distorted octahedrons in two compounds. The dc magnetic determinations reveal that ferromagnetic coupling between two metal centers with J = 1.31 cm−1 exists in 1, whereas 2 displays weak antiferromagnetic interactions with the coupling constant J of −0.56 cm−1. Frequency-dependent ac susceptibilities in the absence of dc field for 1 suggest slow relaxation of the magnetization with an energy barrier of 13.9 K, signifying that 1 features single-molecule magnet (SMM) behavior. This work presents a rational strategy to fine-tune the magnetic interactions and further magnetization dynamics of the Mn(III)-containing dinuclear units through small structural variations driven by the ingenious chemistry.
Highlights
Two Mn(III) ions is regarded as a sensible operation when the motifs of the dimeric Mn(III) units are taken into consideration
The structure of compound 1 is characterized by single-crystal X-ray diffraction analysis, it crystallizes in the monoclinic system space group P21/c
The apical positions are occupied by two deprotonated oxygen atom (Mn1-O2 = 1.951(2) Å, Mn1-O3 = 1.855(2) Å) from two independent CH3O− anions
Summary
Two Mn(III) ions is regarded as a sensible operation when the motifs of the dimeric Mn(III) units are taken into consideration. Regulating the structure and properties of compounds at molecular level still remains the particular challenge that is resulted from the reaction conditions such as pH, solvent, and temperature exerting significant effects on the structures of target compounds[19,20]. Inspired by the aforesaid considerations, employing an versatility tridentate Schiff-base derivative (N3-benzoylpyridine-2-carboxamidrazone, Hbpad), derived from the condensation of benzoyl hydrazine and 2-cyanopyridine (Fig. 1), two new cases of dimeric Mn(III) units, [Mn2(bpad)2(CH3O)4]n (1) and [Mn2(bpad)2(pa)2]n·2H2O (2), were synthesized with deprotonated methanol molecule and phthalic acid (H2pa) as bridged coligands, respectively. 1 undergoes a self-assembly process depending on subtle reaction condition to yield compound 2 with the methanol species interchanged by pa2− anion (Fig. 2). Compound 1 possesses intramolecular ferromagnetic coupling and slow magnetic relaxation of typical SMMs, while the two Mn(III) centers are antiferromagnetically exchanged in compound 2
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