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Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes.

ABSTRACT: We report the synthesis of [Mn(tacud)₂](OTf)₂ (1) (tacud = 1,4,8-triazacycloundecane), [Mn(tacd)₂](OTf)₂ (2) (tacd = 1,4,7-triazacyclodecane), and [Mn(tacn)₂](OTf)₂ (3) (tacn = 1,4,7-triazacyclononane). Electrochemical measurements on the Mn^III/II redox couple show that complex 1 has the largest anodic potential of the set (E _1/2 = 1.16 V vs NHE, ΔE _p = 106 mV) compared to 2 (E _1/2 = 0.95 V, ΔE _p = 108 mV) and 3 (E _1/2 = 0.93 V, ΔE _p = 96 mV). This is due to the fact that 1 has the fewest 5-membered chelate rings and thus is least stabilized. Magnetic studies of 1-3 revealed that all complexes remain high spin throughout the temperature range investigated (2 - 300 K). X-band EPR investigations in methanol glass indicated that the manganese(II) centers for 2 and 3 resided in a more distorted octahedral geometric configuration compared to 1. To ease spectral interpretation and extract ZFS parameters, we performed high-frequency high-field EPR (HFEPR) at frequencies above 200 GHz and a field of 7.5 T. Simulation of the spectral data yielded g = 2.0013 and D = -0.031 cm^-1 for 1, g = 2.0008, D = -0.0824 cm^-1, |E/D| = 0.12 for 2, and g = 2.00028, D = -0.0884 cm^-1 for 3. These results are consistent with 3 possessing the most distorted geometry. Calculations (PBE0/6-31G(d)) were performed on 1-3. Results show that 1 has the largest HOMO-LUMO gap energy (6.37 eV) compared to 2 (6.12 eV) and 3 (6.26 eV). Complex 1 also has the lowest HOMO energies indicating higher stability.

SUBMITTER: Banerjee A

PROVIDER: S-EPMC8112617 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes.

Banerjee Atanu A Tolla Azam S AS Stjepanovic Slavica S Sevilla Michael D MD Goodsell Justin L JL Angerhofer Alexander A Brennessel William W WW Loloee Reza R Chavez Ferman A FA

Inorganica chimica acta 20181113

We report the synthesis of [Mn(tacud)2](OTf)2 (1) (tacud = 1,4,8-triazacycloundecane), [Mn(tacd)2](OTf)2 (2) (tacd = 1,4,7-triazacyclodecane), and [Mn(tacn)2](OTf)2 (3) (tacn = 1,4,7-triazacyclononane). Electrochemical measurements on the MnIII/II redox couple show that complex 1 has the largest anodic potential of the set (E 1/2 = 1.16 V vs NHE, ΔE p = 106 ...[more]

PMID: 33981118

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Project description:The preparation, structures, and electrochemical and magnetic properties supported by density functional theory (DFT) calculations of three new copper(II) compounds with [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 1,1-dioxide (td) and its radical anion (td·-) are reported: {[CuIICl(td)](μ-Cl)2[CuIICl(td)]} (1), which incorporates only neutral td ligands; [CuIICl(td·-)(td)]·2MeCN (2), which comprises one neutral td and one radical td·-; and PPN[CuIICl(td·-)2]·2DMA (3), where CuII ions are coordinated by two radical anions td·- (DMA, dimethylacetamide; PPN+, the bis(triphenylphosphine)iminium cation). All three compounds show interesting paramagnetic behavior with low-temperature features indicating significant antiferromagnetic coupling. The magnetic properties of 1 are dominated by CuII···CuII interactions (JCuCu) mediated through the Cl- bridges, while the magnetic properties of 2 and 3 are governed mainly by the td·-···td·- (Jtdtd) and CuII-td·- (JCutd) exchange interactions. The structure of 2 features only two major magnetic coupling pathways enabling the fitting of experimental data with Jtdtd = -36.0(5) cm-1 and JCutd = -12.6(2) cm-1 only. Compound 3 exhibits a complex network of magnetic contacts. Attempt to approximate its magnetic behavior using only a local magnetic contacts model resulted in Jtdtd = -5.6(1) cm-1 and two JCutd constants, -12.4(2) and -22.6(4) cm-1. The experimental fitting is critically compared with the results of broken symmetry density functional theory (BS DFT) calculations for inter- and intramolecular contacts. More consistent results were obtained with the M06 functional as opposed to popular B3LYP, which encountered problems reproducing some of the experimental intermolecular exchange interactions. Electrochemical measurements of 2 and 3 in MeCN showed three reversible nearly overlapping redox peaks appearing in a narrow potential range of -600 to -100 mV vs Fc/Fc+. Small differences between the redox events suggest that such compounds may be good candidates for new switchable materials, where the electron transfer between the metal and the ligand center is triggered by temperature, pressure, or light (valence tautomerism).

Dataset Information

Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes.

Publications

Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes.

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