A series of stable and genuinely organic open-shell systems, 7r-conjugated plienoxyl nitro)ride free radicals (hybrid phenoJql riitroxide radicals), have been synthesized and their magnetic properties in the crystalline state investigated, revealing their usefulness as new building blocks for molecular magnetic materials. The salient electronic structure of the hybrid phenoxyl nitroxide radicals is extended Tr-spin delocalization from the nitroxide moiety, mediating the localization effect intrinsic to nitroxide radicals. Five representative hybrid radicals containing an aliphatic, aromatic, and heteroaromatic substituent inthe sidepart wof the compact hybrid radical centers ere synthesized, andtheir lectflar/crYstal structures in theccwrYstall_ine state. were determine X-raY diffraction analyses..sPYectroscoPY). and D rXthbeanhclYbErid radicals.confirmedd. that an unpaired spin delocalizes over, the whole molecular FT calculations for; SR 1H-ENDOR frame including the.nollconiugate.d fragments, suggestingthe possibility of tuning their electronic properties throughsubstituefft effects in the crystalline state. Significant influence of the phenoxylmoiety on the electronic, structure was analyzedin terms of the gtensor calculations. The_.SQUID magffetizatiori measurements revealed that(AFM) (CJ hearing alkyl or aromatic substituefft: behave as 3D Curie Weiss paramagnets. with weak antiferromagne 1 to 2.6 K) or ferromagnetic (FM) ( +0.33 K) spin-spin exchange interactions. On the other hand, heteroaro tically substituted hybrid phenoxyl nitroxide showedsignificant AFM interactions with J/k1 7-25-6 K. The analysis;of the bulk amagnetic Pr Perties based on. the.crYstall graPhic data and DFT calculations revealed competition between the intermolecular. AFM and FM interactions which originate fromthdeirnCer s (l/henofql)"'"Me(flitr.ofti'de) (N)O C. (arom.) infinite ID head -to -tail chains and the C(arom) Carom) head-over-tail forming'; 3D networks in their crystal lattices.