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The Hexakis(N,N'-Dimethylurea)Cobalt(Ii) Cation: A Flexible Building Block for the Construction of Hydrogen Bonded Networks

  • Giannis S. Papaefstathiou , Robby Keuleers , Constantinos J. Milios , Catherine P. Raptopoulou , Aris Terzis , Herman O. Desseyn and Spyros P. Perlepes EMAIL logo

Abstract

The ligand N.N'-dimethylurea (DMU) is used to propagate the octahedral coordination geom- etry of [Co(DMU)6]2+ into 1D and 2D assemblies via a combination of coordinative bonds and interionic hydrogen-bonding. Compounds [Co(DMU)6](ClO4)2 (1), [Co(DMU)6](BF4)2 (2) and [Co(DMU)6](NO3)2 (3) have been prepared from the reactions of DMU and the appropriate hydrated cobalt(II) salts in EtOH. MeCN or Me2CO (only for 1) in the presence of 2,2-di- methoxypropane. Crystal structure determinations demonstrate the existence of [Co(DMU)6]2+ cations and CIO4- , BF4- or NO3- counterions. The great stability of the [Co(DMU)6]2+ cation in the solid state is attributed to a pseudochelate effect which arises from the existence of strong intracationic N-H···O(DMU) hydrogen bonds. The [Co(DMU)6]2+ cations and counterions self- assemble to form a hydrogen-bonded ID architecture in 1, and different 2D hydrogen-bonded networks in 2 and 3. The precise nature of the resulting supramolecular structure is influenced by the nature of the counterion. Two main motifs of intermolecular (interionic) hydrogen bonds have been observed: N-H ···O(ClO4-, NO3-) or N-H ··· F(BF4-) and weak C-H F(BF4- ) or C-H-O(NO3- ) hydrogen bonds. The complexes were also characterized by vibrational spec- troscopy (IR, far-IR. low-frequency Raman). The spectroscopic data are discussed in terms of the nature of bonding and the know;n structures.

Received: 2002-9-9
Published Online: 2014-6-2
Published in Print: 2003-1-1

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