Bis(triphenylphosphine)iminium Salts of Dioxothiadiazole Radical Anions: Preparation, Crystal Structures, and Magnetic Properties

Abstract

Phenanthroline dioxothiadiazoles are redox active molecules that form stable radical anions suitable for the construction of supramolecular magnetic materials. Herein, the preparation, structures and magnetic properties of bis(triphenylphosphine)iminium (PPN) salts of [1,2,5]thiadiazole[3,4-f][1,10]phenanthroline 1,1-dioxide (L), [1,2,5]thiadiazole[3,4-f][4,7]phenanthroline 1,1-dioxide (4,7-L), 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (BrL), and 5,10-dibromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (diBrL) are reported. The preparation of new bromo derivatives of the L: 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (BrL) and 5,10-dibromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (diBrL)—suitable starting materials for further derivatization—are described starting from a commercially available and cheap 1,10-phenanthroline. All PPN salts show antiferromagnetic interactions between the pairs of radical anions, which in the case of PPN(diBrL) are very strong (−116 cm−1; using Ĥ = −2JSS type of exchange coupling Hamiltonian) due to a different crystal packing of the anion radicals as compared to PPN(L), PPN(4,7-L), and PPN(BrL).

1,2,5-Thiadiazole 1,1-dioxides and Their Radical Anions: Structure, Properties, Reactivity, and Potential Use in the Construction of Functional Molecular Materials

“…The most popular methods for the calculation of dioxothiadiazole properties is standard and involve DFT with B3LYP hybrid functional and a 6-311G++(d,p) or 6-311G++(3df,3pd) basis set. As in the case of most organic molecules, it is fast and reliable in reproducing data for UV-vis and IR interpretation that closely resemble experimental results [ 21 , 42 , 45 , 51 , 59 , 60 ]. For EPR spectra simulations, usually a B98 hybrid functional is used instead.…”

“…Table 1 supplements Figure 1 b by providing references to the CSD database and the relevant publications, where the respective compounds are reported [ 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Sulfonyl (>SO 2 ) is a very strong electron-withdrawing group; therefore, compared to thiadiazoles, their dioxidized analogues containing this sulfonyl group are superior when it comes to negative charge accommodation within the heterocyclic ring and the resulting radical anion formation and their stability.…”

“…Several 13 C NMR spectra have been reported for 3,4-disubstituted derivatives; carbon signals originating from 1,2,5-thiadiazole 1,1-dioxide ring appear in the 150–170 ppm range [ 59 , 60 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ] as compared to the 130–160 ppm range for 1,2,5-thiadiazoles [ 69 , 70 , 71 ]. Many compounds were not characterized by 13 C NMR spectroscopy due to their relatively low solubility in common deuterated solvents [ 43 , 45 , 51 , 67 ].…”

Influence of the Increasing Number of Organic Radicals on the Structural, Magnetic, and Electrochemical Properties of the Copper(II)–Dioxothiadiazole Family of Complexes

“…According to DFT calculations, the unpaired electron of the td ·– radical anion is mostly delocalized over the thiadiazole ring and partially localized on the nitrogen atoms of the 1,10-phenanthroline backbone, suggesting the possibility of medium-to-strong metal–radical magnetic interactions in the case of its coordination to paramagnetic metal centers. 54 , 56 In this context, we decided to investigate the magnetic exchange interactions between the paramagnetic transition-metal center and the td ·– radical anions by using a combined experimental and theoretical approach. This is the first report where the dioxothiadiazole-type radical ligand is coordinated to a paramagnetic transition-metal center.…”

Molecular Magnets

“…An important group of molecular magnets are purely organic molecular materials, as they show electric conductivity and non-trivial magnetic properties New examples of organic magnetic materials are presented by Pinkowicz et al [7]. The paper reports the synthesis, crystal structures and magnetic characterizations of a series of six dioxothiadiazole-based radical compounds.…”