A new molecule-based weak ferromagnet of formula Fe[C6H5PO3]·H2O was synthesized. It was characterized by thermogravimetric analysis and UV−visible and infrared spectroscopy, and the magnetic properties were studied using a superconducting quantum interference device magnetometer. The crystal structure of the compound was determined “ab initio” from X-ray powder diffraction data and refined by the Rietveld method. The crystals of Fe[C6H5PO3]·H2O are orthorhombic, space group Pmn21, with a = 5.668(8) Å, b = 14.453(2) Å, c = 4.893(7) Å, and Z = 2. The title compound is isostructural with the previously reported lamellar M[C6H5PO3]·H2O, M = Mn(II), Zn(II), and Cd(II). The inorganic layers are made of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from oxygen of the water molecule. These layers are then separated by bilayers of the phenyl groups, and van der Waals contacts are established between them. The refinement has shown that the phenyl rings are disordered in the lattice. The oxidation state of the metal ion is +2, and the electronic configuration is d6(S = 2) high-spin, as determined from dc magnetic susceptibility measurements from 150 K to room temperature. Below 100 K, the magnetic moment of Fe[C6H5PO3]·H2O rises rapidly to a maximum at TN = 21.5 K, and then it decreases again. The peak at TN is associated with the 3D antiferromagnetic long-range ordering. Below the critical temperature, the title compound behaves as a “weak” ferromagnet, which represents the third type of magnetic materials characterized by having a finite zero-field magnetization, ferromagnets and ferrimagnets being the other two types. The large coercive field (i.e., 6400 G) observed in the hysteresis loop at T = 10 K is rare in molecule-based materials; it can be ascribed to a pronounced spin−orbit coupling for the 5T2g ground state of the Fe(II) ion in the octahedral environment.

Solution equilibria of the binary and ternary systems involving Mn+ ion, adenosine 5‘-triphosphate, and some mono- and dicarboxylic amino acids (Mn+ = CuII, NiII, CoII, LaIII, and CeIII) have been investigated potentiometrically at (25 ± 0.1) °C and I = 0.10 mol dm-3 (KNO3). The formation of the different binary and ternary complexes is inferred from the corresponding titration curves. The stability constants of the various complexes formed were determined and discussed in terms of the nature of both the metal ion and the ligand. Moreover, the stability of the mixed ligand complexes is discussed in relation to that of the corresponding binary complexes of amino acids.

The effect of different organic solvent + water mixtures on the acid dissociation constants of protonated 5-amino-4-(arylazo)-3-methyl-1-phenylpyrazole derivatives were studied. The organic solvents used are methanol, ethanol, acetone, and dimethylformamide. The results obtained were discussed in terms of the solvent characteristics.The pKBH+ values of the dyes in question were determined and found to depend on both the amount and nature of the organic cosolvent. The decrease of the pKBH+ values as the amount of organic solvent in the medium is increased can be accounted for in terms of the high stabilization of the protonated form of the compounds by dispersion forces rather than by hydrogen bonding. Also the effect of solvent polarizability and hydrogen-bonding interaction on the pKBH+ values and thus on the spectra of the charge-transfer band observed have been discussed. The absolute pKBH+ value for each compound despite the presence of more than one basicity center has also been discussed.