Crystal Structure,Magnetic Exchange Interaction,and DFT Study of 2,2′‐(1‐Oxidopyridine‐2,6‐diyl)bis[4,5‐dihydro‐4,4,5,5‐tetramethyl‐3‐oxido‐1H‐imidazol‐1‐oxyl] Hydrate

The structure of a novel oxido‐aminoxyl (=`nitronyl nitroxide') biradical, 2,2′‐(1‐oxidopyridine‐2,6‐diyl)bis4,5‐dihydro‐4,4,5,5‐tetramethyl‐3‐oxido‐1H‐imidazol‐1‐oxyl] hydrate ( 1 ?H₂O) was established by X‐ray analysis in the solid state: monoclinic, space group P2₁/c, Z=4 with a=12.621(4), b=15.704(5), and c=13.001(4) Å, and β=115.202(6)°. Variable‐temperature magnetic susceptibilities show a weak antiferromagnetic interaction between the two oxido‐substituted aminoxyl moieties of 1 , indicative of a singlet ground state. AM1 Calculations located minima for the possible structure based on the X‐ray crystal structure. A hybride density‐functional‐theory calculation with the UB3LYP method from the X‐ray crystal structure establishes the same spin sign in the two aminoxyl moieties and shows that a small spin density is localized at the C‐atoms of the pyridine moiety. These theoretic results are in good agreement with the determined weak antiferromagnetic interaction of 1 .