The role of steric constraints in the formation of rare aqua bridged coordination polymers: Synthesis, characterization and X-ray structures of polymeric, [Cu(2-chlorobenzoate)2(β-picoline)2(μ-H2O)]n and monomeric, [Cu(2-chlorobenzoate)2(γ-picoline)2(H2O)

• Rare aqua bridged polymer and discrete monomer complexes have been synthesized.
• Suitably substituted phenyl rings of both the organic ligands play a key role.
• FT-IR, TG analyses indicate varied strength of bonding of water in two complexes.
• Single crystal X-ray structures confirm the polymeric and monomeric structures.

Reaction of hydrated copper(II) 2-chloro-benzoate with β-/γ-picoline in methanol: water mixture (4:1 v/v) yielded polymeric [Cu(2-chlorobenzoate)2(β-picoline)2(μ-H2O)]n; 1 and monomeric [Cu(2-chlorobenzoate)2(γ-picoline)2(H2O)]; 2. The newly synthesized complexes have been characterized by elemental analyses, FT-IR spectroscopy, UV–Visible spectroscopy, TGA and single crystal X-ray structure determination. X-ray crystallographic analysis revealed that both complexes crystallize in the monoclinic crystal system with space group and unit cell dimensions: C2/c; a = 51.71 Å, b = 10.58 Å, c = 10.02 Å and β = 100.5° for 1 and P21/c; a = 11.81 Å, b = 16.33 Å, c = 13.79 Å and β = 90.77° for 2. Whereas in 1 the presence of constituent and mediating water molecules running along a-axis gives rise to 1-dimensional zig-zag polymer chains, in complex 2, the presence of square pyramidal arrangement of ligands around copper(II) center results in monomeric structure. Various non-covalent interactions like OH⋯O, CH⋯O and CH⋯л have been observed to play a decisive role in the stabilization of crystal lattices in both complexes.

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