The synthesis of new paramagnetic phosphorus-containing compounds, (para-RAD-phenyl)diphenylphosphine and phosphine oxide (RAD = nitronylnitroxide, (BuNO)-Bu-t), is described, Complexation of these phosphines with diamagnetic metal centres yields, for example. intermolecular ferromagnetic interactions with (MO(CO)(5)(phosphine)), antiferromagnetic interactions with [AuCl(phosphine)} and {PdCl2(phosphine)(2)}, a complex with multiple paramagnetic ligands. Ligation of nitronyinitroxide-containing phosphines to paramagnetic metals is hindered by catalytic nitrogen to phosphorus oxo-transfer to form the corresponding iminonitroxide-substituted phosphine oxide. A molecular square containing two nitronylnitroxide-substituted phosphine oxide ligands and two Mn(hfac)(2) units is also described.