The ligand versus solvent behavior of Ni+(C6H6)(3,4) complexes was studied using density functional theory all-electron calculations. Dispersion corrections were included with the BPW91-D2 method using the 6-311+ +G(2d,2p) basis set. The ground state (GS) for Ni+(C6H(6))(3) has three benzene rings 3d-pi bonded to the metal. A two-layer isomer with two moieties coordinated eta(3)-eta(2) with Ni+, and the other one adsorbed by van der Waals interactions to the Ni+(C6H6)(2) subcluster, i.e., a 2 + 1 structure, is within about 8.4 kJ/mol of the GS. Structures with 3 + 1 and 2 + 2 ligand coordination were found for Ni+(C6H6)(4). The binding energies (D-0) of 28.9 and 26.0 kJ/mol for the external moieties of Ni+(C6H6)(3,4) are much smaller than that for Ni+(C6H6)(2), 193.0 kJ/mol, obtained also with BPW91-D2. This last D-0 overestimates somehow the experimental value, of 146.7 +/- 11.6 kJ/mol, for Ni+(C6H6)(2). The abrupt fall for D-0(Ni+(C6H6)(3,4)) shows that such molecules are bound externally as solvent species. These results agree with the D-0(Ni+(C6H6)(3)) < 37.1 kJ/mol limit found experimentally for this kind of two-layer clusters. The ionization energies also decrease for m = 2, 3, and 4 (580.8, 573.1, and 558.6 kJ/mol). For Ni+(C6H6)(3,4), each solvent moiety bridges the benzenes of Ni+(C6H6)(2); their position and that of one internal ring mimics the tilted T-shape geometry of the benzene dimer (Bz(2)). The distances from the center of the external to the center of the internal rings for m = 3 (4.686 angstrom) and m = 4 (4.523 angstrom) are shorter than that for Bz(2) (4.850 angstrom). This and charge transfer effects promote the (C delta--H delta+)(int) dipole-pi(ext) interactions in Ni+(C6H6)(3,4); pi-pi interactions also occur. The predicted IR spectra, having multiplet structure in the C-H region, provide insight into the experimental spectra of these ions.