A new copper(II) chelate complex with tridentate ligand: Synthesis, crystal and molecular electronic structure of aqua-(diethylenetriamine-N, N′, N′′)-copper(II) sulfate monohydrate and its fire retardant properties

• The crystals of a new chelate compound of [Cu(deta)H2O]SO4⋅H2O (1) have been synthesized.
• The X-ray (single crystal and powder) structure of 1 has been determined.
• The molecular electronic structure of 1 has been calculated by quantum-chemical method.
• The fire-retardant properties of 1 in solid state have been considered.

The crystals of a new aqua-(diethylenetriamine-N, N′, N′′)-copper(II) sulfate monohydrate have been synthesized by direct interaction of solid copper(II) sulfate pentahydrate with diethylenetriamine (deta). The crystal structure of [Cu(deta)H2O]SO4⋅H2O (1) has been determined by X-ray diffraction methods at 100 K and characterized using X-ray powder diffraction pattern: space group P  1¯, a = 7.2819(4), b = 8.4669(4), c = 8.7020(3) Å, α = 83.590(3), β = 89.620(4), γ = 84.946(4)°, Z = 2. The environment of the Cu(II) atom is a distorted, elongated square pyramid which consists of three nitrogen atoms of the deta molecule and oxygen atom of the water molecule in the basal plane of the square pyramid (the average lengths of the in-plane Cu–N and Cu–O bonds are 2.00 Å). The apical position of the coordination polyhedron is occupied by complementary oxygen atom of the sulfate anion (the length of the axial Cu–O bond is 2.421(1) Å). The crystal packing is governed by strong hydrogen bonds of O–H⋯O and N–H⋯O types. The ab initio quantum-chemical calculations have been performed by the restricted Hartree–Fock method with a basis set 6-31∗G using the structural data of [Cu(deta)H2O]SO4⋅H2O. It has been ascertained that the degenerate d-orbitals of the Cu2+ ion split under the co-action of both the square-pyramidal coordination and the chelation. It is significant that visually observed crystals color (blue-violet) of the [Cu(deta)H2O]SO4⋅H2O complex is in good agreement with the calculated value of wavelength of visible light (λ = 5735 Å) which is closely related to the energy of the absorbed photon (Δ = 2.161 eV). Furthermore, the stereo-chemical aspect of influence of the CuSO4 upon combustibility of modified epoxy-amine polymers has been scrutinized.

X-ray and quantum-chemical investigation of 1: (a) view of the synthesized single crystals; (b) discrete unit of copper(II) chelate complex; (c) 3d-AOs splitting by square-pyramidal crystal field in chelate-bonded Cu2+ ion.Figure optionsDownload as PowerPoint slide