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Self‐Assembly of Cobaloximes and Rhodoximes with 3‐Aminophenylboronic Acid: A Molecular Triangle and a Polymer
Author(s) -
Dreos Renata,
Nardin Giorgio,
Randaccio Lucio,
Siega Patrizia,
Tauzher Giovanni
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200211)2002:11<2885::aid-ejic2885>3.0.co;2-5
Subject(s) - chemistry , crystallography , supramolecular chemistry , pyridine , cobalt , dissolution , boron , inorganic chemistry , crystal structure , medicinal chemistry , organic chemistry
The reactions of methylaquacobaloxime and ethylaquacobaloxime with 3‐aminophenylboronic acid in water produce supramolecular triangles 3a and 3b respectively, through the reaction of boron with the oxime oxygens of the alkylcobaloxime and the coordination of pyridine to cobalt. The reaction is reversible and strongly pH dependent. The complexes 3a and 3b precipitate immediately from the solution at pH 7, but dissolve quickly at both acidic (below 4) and basic (above 9) pH values. The aggregates are re‐formed by readjusting the pH to neutrality and the precipitation‐dissolution cycle may be repeated several times without an apparent decrease in yield. The complexes were fully characterised by 1 H and 13 C NMR spectroscopy. The X‐ray structure shows that the neutral chiral supramolecule 3a is a triangle of cobalt atoms with an approximate C 3 symmetry. The side of the triangle is about 9.5 Å. The ring closure is ensured by the torsion angles around the B−C and C−NH 2 bonds, which vary in the range 25−30° and 97−109°, respectively. The reaction of methylaquarhodoxime with 3‐aminophenylboronic acid in water at pH 7 results in the displacement of H 2 O by 3‐aminophenylboronic acid only. The polymeric form 4 precipitates from CD 3 OD in the NMR tube with time. The X‐ray structure shows that 4 is a polymeric species with a zig‐zag chain arrangement, with Rh ··· Rh distances of 9.2 Å. The chain arrangement is characterized by torsion angles around the B−C and C‐NH 2 bonds of 61° and 92°, respectively. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)