Complexes of Acridine and 9-Chloroacridine with I2: Formation of Unusual I6 Chains through Charge-Transfer Interactions Involving Amphoteric I2

✍ Scribed by Elizabeth L. Rimmer; Rosa D. Bailey; Timothy W. Hanks; William T. Pennington

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 248 KB
• Volume: 6
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20001117)6:22<4071::aid-chem4071>3.0.co;2-#

✦ Synopsis

Acridine and 9-chloroacridine form charge-transfer complexes with iodine in which the nitrogen-bound I 2 molecule is amphoteric; one end serves as a Lewis acid to the heterocyclic donor, while the other end acts as a Lewis base to a second I 2 molecule that bridges two acridine ´I2 units. In the acridine derivative [(acridine ´I2 ) 2 ´I2 , 1], the dimer has a ªzigzagº conformation, while in the 9-chloroacridine derivative [(9-Cl-acridine ´I2 ) 2 ´I2 , 2], the dimer is ªC-shapedº. The thermal decomposition of the two complexes is very different. Compound 1 loses one molecule of I 2 to form an acridine ´I2 intermediate, which has not been isolated. Further decomposition gives acridine as the form II polymorph, exclusively. Decomposition of 2 involves the loss of two molecules of I 2 to form a relatively stable intermediate [(9-Cl-acridine) 2 ´I2 , 3]. Compound 3 consists of two 9-Cl-acridine molecules bridged through N ´´´I charge-transfer interac-tions by a single I 2 molecule. This compound represents the first known example, in which both ends of an I 2 molecule form interactions in a complex that is not stabilized by the extended interactions of an infinite chain structure. The ability of the terminal iodine of an N-bound I 2 to act either as an electron donor (complexes 1 and 2) or as an electron acceptor (complex 3) can be understood through a quantum mechanical analysis of the systems. Both electrostatic interactions and the overlap of frontier molecular orbitals contribute to the observed behavior.