The new Schiff base ligand 2-chlorobenzaldehyde thiosemicarbazone (L, 1) has been synthesized and characterized by spectral techniques and single-crystal X-ray analysis. Crystals of 1 are monoclinic, space group P21/n with a=12.964(4) Å, b=5.131(5) Å, c=4.970(1) Å, β=94.32(2)°, and Z=4. The thiosemicarbazone moiety adopts a configuration with N(1) cis to N(3) and places the E configuration about both the bonds C(1)-N(2) and C(2)-N(3). The monodentate behavior of the neutral ligand (L) has been investigated in two cadmium halides CdL2 Br2 (2) and CdL2I2 (3). Compound 2 crystallizes in space group Cc with a =8.175(1) Å, b=14.176(1) Å, c=21.073(1) Å, β=94.02(1)°, and Z=4. Compound 3 crystallizes in space group P1h with a=10.9577(1) Å, b=16.174(1) Å, c=7.878(1) α=100.50(1)°, β=109.39(1)°, γ =83.67(1)°, and Z= 2. The coordination geometry about the cadmium(II) atom in compound 2 conforms to a tetrahedral configuration with two sulfur atoms from two unequivalent neutral ligands and two bromide atoms. Whereas the coordination geometry about the cadmium(II) atom in compound 3 is (4+1) distorted trigonal bipyramidal with two iodide atoms and one sulfur atom in the equatorial plane, the other thiosemicarbazone sulfur and the iodide atom I(1a) of an adjacent moiety occupy the axial positions. Compound 2 exhibits powder SHG efficiencies ca. 20 times that of urea, whereas compound 3 does not exhibit any SHG efficiency. Theory and experiment suggested that intermolecular contact is the main factor controlling the SHG efficiencies of compounds.