A Solvent-Controlled Switch of Manganese Complex Assemblies with a β-Diketonate-Based Ligand

Abstract

The coordination properties of the new polynucleating ligand H 3 L1 (1,3-bis(3-oxo-3-phenylpropionyl)-2-hydroxy-5-methylbenzene) with Mn II/III are described. Depending on the solvent used, the reaction of H 3 L1 with Mn(OAc) 2 yields either of the two new multinuclear assemblies [Mn 2 (HL1) 2 (py) 4 ] (1) and [Mn 3 (HL1) 3 ] (2), as revealed by X-ray crystallography. The structure of 2 is remarkable in that it shows a unique asymmetric triple-stranded helicate. Complexes 1 and 2 can be interconverted by controlling the solvent of the reaction system, and therefore, this ensemble constitutes an interesting externally addressable switch. In the presence of Mn III /pyridine, partial degradation of H 3 L1 occurs via oxidative cleavage, and the new complex [Mn 2 (L2) 2 (py) 4 ] (3) is formed. The crystal structure of this complex has shown the fully deprotonated form of the new donor H 3 L2 (3-(3-oxo-3-phenylpropionyl)-5-methylsalicylic acid). From the same reaction, the Mn II complex 1 is also obtained. A rational synthesis of H 3 L2 is reported, and this has been used to prepare 3 in high yields, directly from its components. Variable-temperature magnetic susceptibility ( m ) measurements were performed on complexes 1−3 under a magnetic field of 1 kG. The data for each complex were fit to the appropriate m vs T theoretical equation, respectively. In 1, the Mn II ions are uncoupled, with g ) 2.01. The data from 2 were fit by assuming the presence of an exchange coupled Mn II ‚‚‚Mn II pair next to a magnetically isolated Mn II center. The fit gave J ) −2.75 cm -1 , g 12 ) 1.97, and g 3 ) 1.92, respectively. In 3, two models fit the experimental data. In the most satisfactory, the Mn III ions are coupled antiferromagnetically with J ) −1.48 cm -1 and g ) 1.98 and a term for weak ferromagnetic intermolecular exchange is included with zJ′ ) 0.39 cm -1 . The other model contemplates the presence of two uncloupled zero field split Mn III ions.

Complexes of a novel multinucleating poly-β-diketonate ligand

“…Their single crystal X-ray structure shows that the ligand is deprotonated preferentially at the diketone units to chelate the metals, the phenol moieties retaining their protons. Therefore, a direct comparison can be established between the series of compounds presented here and the analogous series previously reported with H 3 L, 15,17,20 in terms of structure and magnetic properties. (2 g) were activated at 180 °C under vacuum over 2 h in a 500 mL three-necked round-bottom flask.…”

Dinuclear manganese(iii) complexes with bioinspired coordination and variable linkers showing weak exchange effects: a synthetic, structural, spectroscopic and computation study

“…Of note are the di-Mn III complexes with two salen-type ligands separated by one or two xanthene spacer(s), in which the Mn⋯Mn separation was ∼5.1 Å, 26 and with two salicaldehyde/diketonatederived ligands in which the Mn⋯Mn separation was ∼5.3 Å, and Mn-Mn exchange interactions were observed. 27,28 Also notable are di-Mn II expanded porphyrins with Mn-Mn distance of 5.4 Å, 29 and di-Mn II complexes of bis( pentadentate) ligands derived from bis-tacn species with longer Mn⋯Mn distances (≥6.8 Å) 30 with no evidence of coupling between paramagnetic centres.…”

Synthetic, structural, electrochemical and solvent extraction studies of neutral trinuclear Co(ii), Ni(ii), Cu(ii) and Zn(ii) metallocycles and tetrahedral tetranuclear Fe(iii) species incorporating 1,4-aryl-linked bis-β-diketonato ligands

“…2 More recently, there has also been increasing interest in the metallosupramolecular structural aspects of such systems. 3,4 In a parallel development, several groups have extended the chemistry of such systems by incorporating more than one b-diketone motif, [5][6][7][8][9][10][11][12] or a related malonate motif, 13 into extended ligand structures before investigating their metal ion chemistry. For example, we [14][15][16][17][18][19] and others 20,21 have recently reported the use of a series of bis-bdiketone ligands of types H 2 L 1 and H 2 L 2 for the construction of a variety of new metallo-supramolecular arrays.…”