Synthesis and magnetic properties of stable nitroxyl tri-radicals

Several stable nitroxyl tri-radicals, such as tris-α, α′, α″-(t-butylnitroxyl alkyl)mesitylene (1) and N,N′,N″-mesitylenylidenetris (4-amino-2,2,6,6-tetramethylpiperidinyloxy) (2), were synthesized by either an addition reaction of alkyl Grignard reagents with corresponding trinitrone molecules or the condensation reaction of 4-amino-2,2,6,6-tetramethylpiperidinyloxy with 1,3,5-benzenetricarboxaldehyde (trimesic aldehyde). The χmT (χm = molar magnetic susceptibility) value was found to increase slightly as the temperature decreased. It reached a maximum value of 1.01 emu-mol−1K at 45 K followed by a sharp decline of the χmT value, indicating the existence of intermolecular antiferromagnetic interactions (θ = −1.91 K) in this molecular system. The effective magnetic moment was found to be 2.85 μB.