Abstract
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).
Highlights
Over the past two decades, the molecular magnetism community has advanced from studying the basic rules governing the magnetic coupling in paramagnetic molecules toward the design and synthesis of multifunctional molecular materials.[1]
We present the experimental and theoretical survey of the structural, electrochemical, and magnetic properties of three new CuII−td complexes with an increasing number of coordinated td·−
In the anionic radical form, on the other hand, it takes control of the magnetic properties of compounds 2 and 3 and enables the construction of magnetically challenging systems. This is due to its strong tendency to form π−π contacts which are very efficient magnetic interaction pathways as was demonstrated experimentally and by broken symmetry (BS) density functional theory (DFT) theoretical calculations
Summary
Over the past two decades, the molecular magnetism community has advanced from studying the basic rules governing the magnetic coupling in paramagnetic molecules toward the design and synthesis of multifunctional molecular materials.[1]. Among many different functionalities of radical-based magnetic compounds, the following seem to be the most popular: electronic conductivity,[12−14] long-range magnetic ordering,[15−19] valence tautomerism,[6,20−22] photomagnetism,[20,23−28] luminescence,[29−32] and single molecule and single chain magnet behavior (SMM and SCM).[3,33−36]
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