Reaction of m- or p-pyridyl nitronyl nitroxide (m- or p-PYNN) with HBr gas gave a 2:1 complex between them. The IR spectra of (m- and p-PYNN)(2)HBr indicates an intermolecular [NHN](+) hydrogen bond between two pyridyl rings. (m-PYNN)(2)HBr shows ferromagnetic properties, while the p-isomer does antiferromagnetic properties. Furthermore, the HCl salt of phenyl-4-pyridylcarbene was generated by irradiation of the diazo precursor. The ESR spectrum shows signals of triplet and quintet spin species, latter of which indicates a ferromagnetic interaction between the triplet carbenes.