Structural and electronic properties of solid Cu-2(NO3)(OH)(3) are investigated via first-principle calculations combined with a self-consistent geometry optimization of the atomic positions. The calculated structure is in very good agreement with available X-ray experimental determination. Wt found that for total spin S = 0, each layer containing the Cu atoms has an antiferromagnetic character, resulting from parallel or antiparallel alignment between spin densities located on the Cu centers. The implications of these findings on the manifestation of three-dimensional antiferromagnetic order at low temperatures are discussed in connection with experimental work.