The compounds formed by SbCl₃ and the 1-halonaphthalene in the crystalline state may provide information on some of the factors involved in molecular complex formation. The gradation in both the size and the electronegativity of the naphthalene substituent permits comparisons internally and externally with the parent 2SbCl₃.naphthalene complex. Other molecular complexes are briefly surveyed. (l:l) SbCl₃ l-bromonaphthalene forms triclinic crystals, PT. with a=9.08, b=11.98, c=12.72 Å, ∝=113.1, β=93.6, γ 91.5° V=1268 ų, z=4. Photographic Mo data refined to R=0.14 for 591 reflections. The crystal structure is built up of double lawyers of SbCl₃ molecules alternating in the "c" direction with double layers of 1-bromonaphthalene molecules, tilted 25° to [010] . The SbCl₃ molecules form dimers, further bridged into infinite chains. The Sb atoms are in a distorted pentagonal bipyramid environment, with Å bonded chlorine atom and the aromatic π-system in axial positions at 2.38 and 3.32 Å. The lone pair of electrons is stereochemically inactive. (2:l)SbCl₃.l-chloronaphthalene forms monoclinic crystals, Cc, with a=16.059, b=9.525, c=11.674 Å, β=98-63°, V=1765 ų, z=4 , Diffractometer Mo data refined to R=0.l25 for 1035 reflections. The structure is built up of double layers of SbCl₃ molecules alternating in the "a" direction with single layers of l-chloronaphthalene molecules, tilted 25° to [00l] . SbCl₃ molecules form dimers, further bridged into infinite chains. Two non-equivalent SbCl₃ molecules are situated near to the l-chloronaphthalene molecule (?3.32 Å) - Sb(l) is close to the ring carrying the chlorine atom whereas ,Sb(2) is close to the other ring on the opposite side. The Sb atom is in-a distorted, pentagonal bipyramid environment, with a bonded chlorine atom and the aromatic π-system in axial positions at 2.32 and 3.32 Å respectively. Again the lone pair of electrons is stereochemically inactive. ,(l:l)SbCl₃.1-iodonaphthalene forms triclinic crystals, PI, with a=l3.15, b=7.65, C=15-01 Å, ∝ -104.7°, β =102.2°, γ =108-5°, V=1312 ų,Z-4. Photographic Mo data refined to R=0.20 for 678 reflections having l even. With l odd serious streaks appear suggesting a partly disordered structure. The crystal structure is built up of double layers of SbCl₃ molecules alternating in the "a" direction with double layers, of l-iodonaphthalene molecules, tilted ~ 25° to [010] . The two SbCl₃ molecules are linked to one another by Sb...Cl bridging, which are Part of an infinite chain. Plane-to-plane molecular stacking of l-C₁₀H₇I is observed. The Sb environment is similar to that in the l-bromonaphthalene compound. It seems that the SbCl₃:l-halonaphthalene complexes may be linked by an electron-donor-acceptor interaction where an electron donation occurs from the π-system to the antimony atom.