The adducts AsX3 . nL (where L is 2,2’-bipyridine (Bipy) or 2,2’-bipyridine N,N’-dioxide (BipyO2), X is Cl, Br or I and n is 1, 1.5 or 2) have been synthesized and characterized by melting points, elemental analysis, thermal studies and infrared spectroscopy. By means of calorimetric measurements in solution, the following thermochemical parameters have been determined : the standard enthalpies for the Lewis acid/base reaction (DELTA(r)H(PHI)), the standard enthalpies of formation (DELTA(f)H(PHI)), the standard enthalpies of decomposition (DELTA(D)H(PHI)), the lattice standard enthalpies (DELTA(M)H(PHI)) and the enthalpies of the Lewis acid/base reactions in the gaseous phase (DELTA(r)H(PHI)(g)). The mean standard enthalpies of arsenic-nitrogen and arsenic-oxygen bonds have been estimated.