Journal
CRYSTENGCOMM
Volume 16, Issue 29, Pages 6730-6744Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4ce00387j
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Funding
- IISER, Mohali
- MHRD
- CSIR, India
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In exploring the chemistry of reduced Schiff base derivatives of amino acids with Cu(II) ions, a series of homochiral two-dimensional (2D) coordination polymers (CPs) with a unique loop-like structure comprised of five Cu(II) centers, {[Cu-2(Hsersal)(2)(H2O)]center dot 2.5H(2)O}(n), (1), {[Cu-2(Hser-5OMe-sal)(2)(H2O)]center dot DMF}(n) (2), [Cu-2(Hser-5NO(2)-sal)(2)(H2O)](n) (3), {[Cu-2(Hser-5Cl-sal)(2)(H2O)]center dot 2H(2)O}(n) (4), {[Cu-2(Hser-3Cl-sal)(2)(H2O)]center dot 3H(2)O}(n) (5) and {[Cu-2(Hser-o-Van)(2)(H2O)]center dot 3H(2)O}(n) (6) [where H(3)sersal = N-(2-hydroxybenzyl)-serine, H(3)ser-5OMe-sal = N-(2-hydroxy-5-methoxybenzyl)-serine, H(3)ser-5NO(2)-sal = N-(2-hydroxy-5-nitrobenzyl)-serine, H(3)ser-5-Cl-sal = N-(2-hydroxy-5-chlorobenzyl)-serine, H(3)ser-3-Cl-sal = N-(2-hydroxy-3-chlorobenzyl)-serine, H(3)ser-o-van = N-(2-hydroxy-3-methoxybenzyl)-serine], have been isolated in good yields from the reaction of a methanolic solution of CuSO4 center dot 5H(2)O and potassium salt of the respective ligands (in a 1 : 1 ratio) either at room temperature or under reflux. In these CPs, the two Cu(II) centers have different coordination environments with one coordinated to a water molecule. Using a bifunctional linker, such as 4,4'-bipyridine, four of these 2D CPs are converted in methanol under reflux to the corresponding 2D supramolecular coordination complexes (SCCs) constructed through very strong hydrogen bonding interactions, [Cu-2(4,4'-bpy)(Hsersal)(2)]center dot 2H(2)O (7), [Cu-2(4,4'-bpy)(Hser-5-OMe-sal)(2)]center dot 6H(2)O (8), [Cu-2(4,4'-bpy)(Hser-5-NO2-sal)(2)]center dot H2O (9) and [Cu-2(4,4'-bpy)(Hser-5-Cl-sal)(2)]center dot 4H(2)O DMF (10). This chemical conversion of a CP to an SCC is unknown in the literature and indicates the hierarchical importance of coordination and hydrogen bonds in their formation. The complexes are structurally characterized by elemental analysis, UV-Vis spectroscopy, circular dichroism, IR and Raman spectroscopy, ESI mass spectrometry, single crystal and powder X-ray diffraction, polarimetry and thermogravimetric analysis. A magneto-structural correlation for the change from 1 to 7 is established through variable temperature magnetic susceptibility measurements (2-390 K) indicating strong antiferromagnetic coupling (2J = -278 cm(-1)) in 1 and no interaction in 7 between the Cu(II) centers. As an example, water adsorption studies of 1 and 7 were carried out to demonstrate the porous nature of the SCCs compared to the CPs.
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