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Complexes of Acridine and 9‐Chloroacridine with I 2 : Formation of Unusual I 6 Chains through Charge‐Transfer Interactions Involving Amphoteric I 2
Author(s) -
Rimmer Elizabeth L.,
Bailey Rosa D.,
Hanks Timothy W.,
Pennington William T.
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20001117)6:22<4071::aid-chem4071>3.0.co;2-#
Subject(s) - acridine , chemistry , dimer , molecule , stereochemistry , crystallography , photochemistry , organic chemistry
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⋅I 2 units. In the acridine derivative [(acridine⋅I 2 ) 2 ⋅I 2 , 1 ], the dimer has a “zigzag” conformation, while in the 9‐chloroacridine derivative [(9‐Cl‐acridine⋅I 2 ) 2 ⋅I 2 , 2 ], the dimer is “C‐shaped”. The thermal decomposition of the two complexes is very different. Compound 1 loses one molecule of I 2 to form an acridine⋅I 2 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 ⋅I 2 , 3 ]. Compound 3 consists of two 9‐Cl‐acridine molecules bridged through N⋅⋅⋅I charge‐transfer interactions 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.