Crystallography and magnetism of radicals with hindered hydroxyl groups: 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl.
Radicals form networks of OH... ON and OH...Me(nitroxide) interactions. In 2, a frustrated network forms with insufficient N-O units to form extended chain interactions. The magnetism of 1 fits a 1-D Heisenberg model with J/k=-25 J mol(-1), while 2 shows more complex exchange behaviour consistent with its disordered crystal lattice.
Crystal structure and magnetic properties of hydrogen bonded charge-transfer compound – TMPD:TCNB
Abstract 1,2,4,5-Tetracyanobenzene (TCNB), a moderate electron acceptor, reacts readily with N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), a strong electron donor, to form black colored TMPD:TCNB complex when treated in 1:1 molar ratio. Single crystal X-ray diffraction studies on this complex showed that molecule of TMPD and TCNB are alternately stacked with an interplanar distance of 3.4 A between them. The structure of the complex does not seem to show usual π–π interaction between the two aromatic rings, but indicates the presence of n–π interaction localized between the nitrogen atoms of TMPD and the cyano groups of TCNB. Along with this a prominent presence of CN···HAr hydrogen bonded ribbon network between nitrogen of cyanide moiety and hydrogen of neighboring aromatic carbon is observed with distance of 2.610 A and angle of 147.19°. Magnetic measurements on the powdered compound using SQUID magnetometer (5–20 K) showed that the complex is weakly antiferromagnetic (θ = −0.85 K). To my best knowledge CN···HAr interaction amongst electron acceptor molecules, to form a ribbon-like network, has not been observed before for a magnetic complex.
Atomic parameters for paramagnetic resonance data
Abstract The atomic parameter ψ2(0) and the isotropic hyperfine interaction A for unit spin density in the corresponding s orbital are calculated for the most abundant nuclei of the elements from helium to bismuth from the Hermann-Skillman wavefunction. Angular factors for p, d, and f orbitals are also given, and the application of the results is illustrated by the interpretation of the hyperfine intractions in the radicals PbF63− and YbH.