Solutions of BF3 in liquefied Ar, N-2, and Ar/N-2 mixtures have been investigated using Monte Carlo simulations and infrared cryospectroscopy. The simulations show that in pure liquefied Ar only solvation of BF3 occurs, but that in solutions that contain N-2, also van der Waals complexes of the types BF3. N-2 and N-2. BF3. N-2 are formed. The fractions of monomer and complexes are calculated to vary with temperature and with concentration of N-2. In the infrared spectra of BF3 issolved in liquid Ar/N-2 mixtures, the BF3 bands have complex structures, which in the case of upsilon(3) clearly resolve into triplets. This is attributed to the formation of 1:1 and 1:2 complexes of BF3 with N-2 molecules. The evolution of the relative intensities of the components of the BF3 multiplets as a function of temperature and as a function of concentration agree with the Monte Carlo predictions. From a temperature-dependent study, the complexation enthalpy for BF3. N-2 in liquefied argon was determined to be -4.8(5) kJ mol(-1).