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).