PREPARATIONS AND STRUCTURAL CORRELATIONS FOR THE COMPLEXES OF M(III) HALIDES (M = AS, SB, BI) WITH CROWN-ETHERS - STRUCTURES OF ASCL3.12-CROWN-4, ASCL3.15-CROWN-5, SBCL3.12-CROWN-4 AND BICL3.15-CROWN-5-ASTERISK AND AN EVALUATION OF RELATIVE BINDING STRENGTHS FOR CROWN LIGANDS

The preparations and structures of four new complexes are reported in the family of MCl3.crown complexes (M = As, Sb, Bi; crown = 12-crown-4 , 15-crown-5, 18-crown-6). The structures of the eight isolable member s of the family are compared and trends established. The M-O bonding i s much weaker than the M-Cl bonding, becoming stronger in the order Bi > Sb > As and 12-crown-4 > 15-crown-5 > 18-crown-6. The Cl-M-Cl angle s are reduced compared to those in the free halides, but the M-Cl bond s are only slightly lengthened. The crown torsion angles show characte ristic patterns involving gauche C-C bonds and alternating gauche and anti C-O bonds.