The complex p-NPNN . Cu(hfac)(2) (p - NPNN =p-nitrophenyl nitronylnitroxide and hfac=hexafluoroacetylacetonate) crystallizes into the triclinic P (1) over bar space group [a=12.515(3) Angstrom, b=12.540(2) Angstrom, c=11.610(3) Angstrom, alpha=106.18(2)degrees, beta=119.15(2)degrees, gamma=91.14(2)degrees, V=1501.7(6) Angstrom(3), Z=2]. The structure consists of an alternating chain of p-NPNN and Cu(hfac)(2) in which p-NPNN bridges two nonequivalent copper ions occupying the axial positions. The chains are connected by a pi-pi and head-to-tail overlap of the p-NPNN molecules, resulting in a two-dimensional network. The high-temperature magnetic susceptibilities can be interpreted in terms of a ferromagnetic intrachain interaction of J/k(B)=14.3 K and an antiferromagnetic interchain interaction of zJ’/k(B)=-2.6 K. The observed interchain interaction which would originate in the overlap of p-NPNN is much stronger than those in the related Cu(II) materials reported so far. The low-temperature magnetic susceptibilities indicate an antiferromagnetic order at T-N=1.22+/-0.01 K, followed by an enhancement of the susceptibility below T-c=0.6+/-0.1 K, probably due to a spin canting.