As a novel radical building block possessing multiple hydrogen bond functionality, we have designed and synthesised diaminotriazine-substituted nitronyl nitroxide (DAT-NN; 1). The diaminotriazine moiety of 1 forms two kinds of hydrogen bonding and molecule 1 forms an S = 1/2 uniform antiferromagnetic Heisenberg chain with the exchange interaction of J/k_B = −15.3 K in the crystalline solid, which is attributable to close contacts between the nitronyl nitroxide oxygen atoms. ¹H-ENDOR spectroscopy has shown that the triazine moiety has little significant spin density. Thus, the diaminotriazine moiety plays a role primarily in determining the molecular packing instead of propagating intermolecular magnetic interactions in the crystalline solid.