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The hexakis(N,N ‘-dimethylurea)cobalt(II) cation: A flexible building
block for the construction of hydrogen bonded networks
Papaefstathiou, GS
Keuleers, R
Milios, CJ
Raptopoulou, CP
and Terzis, A
Desseyn, HO
Perlepes, SP
The ligand N,N’-dimethylurea (DMU) is used to propagate the octahedral
coordination geometry 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-dimethoxypropane. Crystal structure
determinations demonstrate the existence of [Co(DMU)(6)](2+) cations
and ClO4- 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 1D
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 spectroscopy (IR, far-IR, low-frequency Raman). The
spectroscopic data are discussed in terms of the nature of bonding and
the known structures.
(EN)
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