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<p>A nine-coordinated hydrazinium holmium(III)–EDTA hydrated complex, formulated as (N<sub>2</sub>H<sub>5</sub>)[Ho(EDTA)(H<sub>2</sub>O)<sub>3</sub>]·2.5H<sub>2</sub>O, was synthesized through two related synthetic routes involving hydrazine hydrate, H₄EDTA, and holmium nitrate in aqueous medium. The crystalline complex was characterized using single-crystal X-ray diffraction (SCXRD), TG–DTA thermal analysis, emission and absorption spectroscopy, CHN analysis and FT–IR spectroscopy. Elemental analysis supports the proposed molecular formula. The electronic spectrum shows ligand-centered UV bands and weak Ho<sup>3</sup>⁺ 4f–4f transitions, confirming the + 3-oxidation state. Fluorescence exhibits characteristic green emission (<sup>5</sup>F₄/<sup>5</sup>S₂ → <sup>5</sup>I₈), indicating efficient ligand-to-metal energy transfer. FT–IR confirms multidentate EDTA coordination and water molecules, while TG–DTA reveals stepwise dehydration and ligand decomposition, forming stable Ho₂O₃ as the final residue. SCXRD analyses revealed the orthorhombic nature of the holmium(III) complex, with crystallization in space group Fdd2. The unit cell parameters are: a = 19.4686(12) nm, b = 35.335(2) nm, c = 12.2845(7) nm, with α = β = γ = 90°. The crystal has Z = 16 formula units per unit cell, a calculated density (Dc) of 1.843&#xa0;mg&#xa0;m⁻<sup>3</sup> and an F(000) value of 4672. Structural analysis revealed that the Ho<sup>3</sup>⁺ ion adopts a nine-coordinated by two tertiary nitrogen atoms from the EDTA ligand, four carboxylate oxygen atoms and three coordinated water molecules, resulting in a distorted dodecahedral geometry. Extensive hydrogen bonding among hydrazinium cations, coordinated and lattice water molecules and EDTA anions stabilizes the crystal packing. In addition, the complex exhibited significant antimicrobial activity against both Gram-positive and Gram-negative bacterial strains, including <i>Escherichia coli</i>, <i>Salmonella typhi</i>, <i>Klebsiella pneumoniae</i> and <i>Pseudomonas</i> species. The compound also demonstrated promising antifungal activity against <i>Aspergillus niger</i> and <i>Candida albicans</i>, indicating its potential as a biologically active lanthanide-based coordination compound.</p> Graphical abstract <p></p> <p>Scheme1: Synthesis method of (N₂H₅)[Ho(EDTA)(H₂O)₃]·2.5H₂O</p>

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Molecular structure and characterization of a novel nine-coordinated hydrated holmium(III)–EDTA complex with hydrazinium cation

  • 期刊论文

  • 发表日期：

    2026年7月7日

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  • K. Naresh,
  • A. Mani,
  • B. Archana,
  • N. Muthulakshmi,
  • S. Jayasree,
  • B. N. Sivasankar,
  • B. Preethi,
  • C. Sivakumar

摘要

A nine-coordinated hydrazinium holmium(III)–EDTA hydrated complex, formulated as (N2H5)[Ho(EDTA)(H2O)3]·2.5H2O, was synthesized through two related synthetic routes involving hydrazine hydrate, H₄EDTA, and holmium nitrate in aqueous medium. The crystalline complex was characterized using single-crystal X-ray diffraction (SCXRD), TG–DTA thermal analysis, emission and absorption spectroscopy, CHN analysis and FT–IR spectroscopy. Elemental analysis supports the proposed molecular formula. The electronic spectrum shows ligand-centered UV bands and weak Ho3⁺ 4f–4f transitions, confirming the + 3-oxidation state. Fluorescence exhibits characteristic green emission (5F₄/5S₂ → 5I₈), indicating efficient ligand-to-metal energy transfer. FT–IR confirms multidentate EDTA coordination and water molecules, while TG–DTA reveals stepwise dehydration and ligand decomposition, forming stable Ho₂O₃ as the final residue. SCXRD analyses revealed the orthorhombic nature of the holmium(III) complex, with crystallization in space group Fdd2. The unit cell parameters are: a = 19.4686(12) nm, b = 35.335(2) nm, c = 12.2845(7) nm, with α = β = γ = 90°. The crystal has Z = 16 formula units per unit cell, a calculated density (Dc) of 1.843 mg m⁻3 and an F(000) value of 4672. Structural analysis revealed that the Ho3⁺ ion adopts a nine-coordinated by two tertiary nitrogen atoms from the EDTA ligand, four carboxylate oxygen atoms and three coordinated water molecules, resulting in a distorted dodecahedral geometry. Extensive hydrogen bonding among hydrazinium cations, coordinated and lattice water molecules and EDTA anions stabilizes the crystal packing. In addition, the complex exhibited significant antimicrobial activity against both Gram-positive and Gram-negative bacterial strains, including Escherichia coli, Salmonella typhi, Klebsiella pneumoniae and Pseudomonas species. The compound also demonstrated promising antifungal activity against Aspergillus niger and Candida albicans, indicating its potential as a biologically active lanthanide-based coordination compound.

Graphical abstract

Scheme1: Synthesis method of (N₂H₅)[Ho(EDTA)(H₂O)₃]·2.5H₂O