Flexibility in co-ordinative behaviour of N-(3-hydroxypropyl)ethane-1,2-diamine toward cadmium(ii) halides: syntheses, crystal structures and solid state thermal studies

Abstract

One new two-dimensional and two one-dimensional organic/inorganic composite coordination polymers have been synthesised by the reaction of cadmium(II) halides with N-(3-hydroxypropyl)ethane-1,2-diamine (L) and structurally characterised. [Cd(L)Cl₂]_n (1) is a two-dimensional sheet which is built from intersecting zigzag chains and forms a honeycomb like (6,3) net where each octahedral cadmium is linked with two bridging chloride atoms, one pendant chloride atom, two chelated nitrogen atoms of L and an oxygen atom from a neighbouring ligand; each cadmium(II) acts as a branching centre. [Cd(L)Br₂]_n (2) is a bromo bridged one-dimensional chain in which the non-chelated part of ligand L binds a neighbouring cadmium(II) centre resulting in an alternating array of four- and twelve-membered rings. [Cd(L)I₂]_n (3) is an iodo bridged one-dimensional network of alternating octahedral (CdN₄I₂) and tetrahedral cadmium(II) (CdI₄) centres. Upon heating the complexes exhibit an irreversible endothermic phase transition [95–133 °C, ΔH = 29.5 kJ mol⁻¹ for (1); 83–128 °C, ΔH = 22.5 kJ mol⁻¹ for (2) and 91–128 °C, ΔH = 15.5 kJ mol⁻¹ for (3)] yielding transparent films of CdLCl₂ (1a), CdLBr₂ (1b) and CdLI₂ (1c) respectively. The derived species (1a, 1b and 1c) do not revert on keeping them in a humid atmosphere (relative humidity ≈ 60%) for several days but exhibit a glass transition upon heating.