A new hybrid salt (C₅H₉N₂)[Cr(C₂O₄)₂ (H₂O)₂].3H₂O, 3,5-dimethylpyrazole Cis diaquadioxala-tochromate(III) trihydrate, has been prepared by slow evaporation at room temperature and characterized by single crystal X-ray diffraction, IR, UV–visible spectroscopies, PXRD and thermogravimetric analyses. Furthermore, the observed crystal morphology was compared to the simulated one using the Bravais-Friedel, Donnay-Harker model. The structure of the title compound consists of [Cr(C₂O₄) ₂ (H₂O) ₂]⁻ mononuclear anions, 3,5-dimethylpyrazole cations and three uncoordinated water molecules. The Cr³⁺ ion is six coordinated in a slightly distorted octahedral environment, by two O atoms from two water molecules and four O atoms of two oxalate anions acting as chelating ligands. The cohesion of the structure is established by intermolecular O–H...O, N–H...O hydrogen bonds which connect ionic entities and water molecules and also by 𝜋–𝜋 stacking interactions between the rings of 3,5-dimethylpyrazole cations. Hence, both coordinated and uncoordinated water molecules play an important role in the hydrogen-bonding system and stabilize the structure.

Tetraaqua bismaleato iron(II) [Fe(C₄H₃O₄)₂ (H₂O)₄], (1) is a new synthetic antimicrobial agent. Thermal analysis shows that the dehydration of the compound occurs in agreement with the structure. The single crystal salt crystallizes in the triclinic space group 𝑃-1 with 𝑎 = 5.171(2) Å, 𝑏 = 7.309(3) Å, 𝑐 = 9.731(3) Å, 𝛼 = 109.15(2)^°, 𝛽 = 115.02(2)^°, 𝛾 = 92.42(1)^°, 𝑉 = 313.6(3) ų and Z = 1. Three dimensional network is formed by strong intermolecular O – H . . . O hydrogen bonds. Magnetic susceptibility measurements of 1 in the range 2–300 K exhibited paramagnetic behavior at high temperature. However, at low temperature, the susceptibility data showed weak antiferromagnetic interactions between the local spins. Antimicrobial activity of 1 was tested. It showed high response against gram-positive and gram-negative bacteria as well as fungi and the MIC and IC50 values ranged from 8 to 256 𝜇g.mL⁻¹ and from 1.38 to 22.19 𝜇g.mL⁻¹, respectively.

Besides the fact that direct synthesis of oxalate-based Mn(II) complexes did not succeed a lot due to the high insolubility of manganese oxalate (Mn^II(C₂O₄) · 2H₂O), a new 2D polymeric Mn(II) salt has been synthesized by slow evaporation at room temperature and its structure has been determined by single-crystalX-ray diffraction. The structure was solved by direct methods and refined to conventional agreement indices. The crystal structure is built from anionic, two-dimensional, honeycomb networks formed by the oxalatebridged Mn(II) ions, interleaved by 2,6-diaminopyridinium cations that are entrapped between the layers. The interactions between adjacent layers result from the extended network of intermolecular hydrogen bonds created by the mentioned cations and water molecules. The complex has been fully characterized by single crystalX-ray diffraction, FT-IR and UV–Vis spectroscopy, Rietveld refinement, TGA–DSC analysis and magnetic susceptibility. The title compound exhibits antiferromagnetic coupling between Mn(II) centres