18-Crown-6 ether templated transition-metal dicyanamido complexes: Synthesis, structural characterization and DFT studies

Reaction of ethanolic solution of hydrated metal salts Mn(NO3)(2)/Fe(BF4)(2) with sodium dicyanamide (dca) and 18-crown-6 ether (18C6) in water results in the isolation of 1:1 associates [Mn(dca)(2)(H2O)(4)]center dot 18C6 (1) and [Fe(dca)(2)(H2O)(4)]center dot 18C6 (2). Single crystal X-ray structure analysis revealed a high degree of iso-structurality between the two 18C6 templated metal complexes (1) and (2) exhibiting second sphere coordination via intermolecular O (water)-H center dot center dot center dot O (crown) hydrogen bonds. The octahedral Mn(II)/Fe(II) complexes are sandwiched between adjacent 18C6 molecules into one-dimensional polymeric chains along the [100] directions, which are further linked through intermolecular O (water)-H center dot center dot center dot N (dca) hydrogen bonds, thus forming a two-dimensional supramolecular framework. The electronic structures of the complexes calculated at the DFT level showed a HOMO-LUMO energy separation of 2.45 eV in (1) and 0.83 eV in (2), which implied a higher kinetic stability of complex (1) than that of (2). (C) 2012 Elsevier B.V. All rights reserved.