A new nickel(II) complex Ni_2(L)_2(2,2?-bipy)_2·5.5H_2O with methy-bicycle[2.2.1]hept- 5-ene-2,3-dicarboxylic acid (H_2L) and 2,2?-bipyridine (2,2?-bipy) as ligands has been synthesized in the mixed solvent DMF and water (v:v = 5:2). It crystallizes in the triclinic space group P1 with a = 10.414(2), b = 12.884(3), c = 16.176(4) A, α = 70.715(5), β = 80.599(5), γ = 77.383(6)o, V = 1989.4(8) A~3, D_c = 1.531 g/cm~3, Z = 2, F(000) = 958, GOOF = 1.028, the final R = 0.0808 and w_R= 0.2036. The crystal structure shows that the whole molecule co...