Structural, spectroscopic and magnetic properties of a novel copper(ii) l-tyrosinato complex

Abstract

The complex [Cu(L-Tyr)₂(H₂O)]·H₂O (1) (L-Tyr = L-tyrosine) was obtained as crystals and characterized by X-ray, spectroscopic (FT-IR, FT-Raman, NIR-vis-UV, and EPR) and magnetic methods. The monomeric complex crystallized in the monoclinic P2₁ symmetry with a = 11.967 (1) Å, b = 5.9986 (4) Å, c = 14.936 (1) Å. The amino N and carboxylate O atoms of chelating L-tyrosinate anions together with the O atom of water molecules create a slightly distorted square pyramidal environment around the Cu(II) ions (τ = 0.11). The distance of about 5.998(1) Å [Cu(L-Tyr)₂(H₂O)] units is involved in a polymeric chain based on N(1)–H⋯O(4)^vi and N(2)–H⋯O(5)^vi hydrogen bonds. The d–d band found in the polycrystalline-reflectance spectrum at 15 700 cm⁻¹ is composed of three ²B₁(d_x2–y2) → ²A₁ (d_z2), ²B₁ → ²B₂(d_xy) and ²B₁ → ²E (d_xz ≈ d_yz) transitions with energies 14 880, 15 800 and 19 950 cm⁻¹, respectively. In DMSO solution the complex preserves its square pyramidal geometry as evidenced by an intensive band at ca. 16 400 cm⁻¹. The EPR spectral parameters for powder (g_‖ = 2.236 and g_⊥ = 2.063) and DMSO frozen solution (g_‖ = 2.250, g_⊥ = 2.055, and A_‖ = 180 G) correspond to an axial symmetry of the Cu(II) coordination geometry with the d_x2–y2 orbital as a ground state of the unpaired electron. Furthermore, the frozen solution spectrum revealed signals corresponding to S = 1 spin states of Cu(II) ions coupled by dipole–dipole interactions with distinctly resolved hyperfine splitting due to two copper nuclei (|D| = 0.0468 cm⁻¹, g_‖ = 2.238, g_⊥ = 2.06 and A_‖ = 85 G). The variable-temperature magnetic susceptibility measurements revealed the existence of a weak ferromagnetic interaction between neighboring copper(II) ions through the N–H⋯O hydrogen bonds.