Using different spectroscopic techniques and computational calculations, we describe the structural and electromagnetic relationship that causes many interesting phenomena within a novel coordination compound with mixed valence manganese (II, III and IV) in its crystal and powder state. The novel compound [MnII MnIII MnIV(HL)2(H2L)2(H2O)4](NO3)2(H2O) 1 was obtained with the Schiff base (E)-2-((2-hydroxybenzylidene)amine)-2-(hydroximethyl)propane-1,3-diol, (H4L), and Mn(NO3)2.4H2O. The coordination reaction was promoted by the deprotonation of the ligand by the soft base triethylamine. The paper’s main contribution is the integration of the experimental and computational studies to explain the interesting magnetic behavior that the mixed valence manganese multimetallic core shows. The results presented herein, which are rarely found for Mn(II), (III) and (IV) complexes, will contribute to the understanding of the magnetic communication generated by the valence electrons and its repercussion in the local geometry and in the overall crystalline structure.

Two compounds [Co2(pa)2(μ1,1‐N3)2]n (1) and [Co4(pa)6(μ1,1‐N3)6] (2), (pa=picolinamide) were obtained and studied by electronic and magnetic spectroscopies. 1 is a polymer and 2 is a tetramer of mixed‐valence CoII/III. The N3− anions act as bridges between cobalt ions in the μ1,1 coordination mode. UV‐Vis spectrum analysis showed the octahedral distortion of the compounds. ESR solution spectra revealed a low‐spin ground state, s=1/2 (dz2 ) for CoII. The energy gap was J>kT between levels, S=0 to S=±1 , of 2; consequently, its transition would not be observed. 1 showed zero‐field splitting of the excited level S=±1 with D∼0.31 cm−1. Hyperfine (59Co, I=7/2) and superhyperfine (14N, I=1) couplings were observed. Magnetic susceptibility studies (3–300 K) revealed antiferromagnetic exchange interactions in 1 and 2 with exchange coupling constants, J1=−108 cm−1 and J2=−20 cm−1, g=2 and s=1/2 , for the Co(2)‐Co(2) magnetic exchange pathways.

Tautomeric equilibria at room temperature were studied for three aromatic imine polyol compounds, previously reported 2-((2-hydroxybenzylidene)amino)-2-(hydroxymethyl)propane-1,3diol 1 and two new compounds 2-(((1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)imino)methyl)benzene-1,4-diol 2 and 3-(((1,3-dihydroxy-2-(hydroxymethyl)propan-2 yl)imino) methyl)benzene-1,2-diol 3. The dynamic behavior of these equilibria is described by a combination of IR, UV-Vis and NMR spectroscopic measurements with DFT and TDDFT calculations in condensed phase. Among the different approaches, the combination of UV-Vis experimental spectra with the oscillator strengths values estimated from TDDFT calculations allowed for the assessment of the tautomeric populations in DMSO and methanol. These results were consistent with different functionals employed GGA, Hybrid and MetaGGA.

The new diamagnetic complex, [Zn2(N3)4(C6H6N2O)2] or [Zn2(pca)2(μ1,1-N3)2(N3)2] was synthesized using pyridine-2-carboxamide (pca) and azido ligands, and characterized using various techniques: IR spectroscopy and single-crystal X-ray diffraction in the solid state, and nuclear magnetic resonance (NMR) in solution. The molecule is placed on an inversion centre in space group P\overline{1}. The pca ligand chelates the metal centre via the pyridine N atom and the carbonyl O atom. One azido ligand bridges the two symmetry-related Zn2+ cations in the end-on coordination mode, while the other independent azido anion occupies the fifth coordination site, as a terminal ligand. The resulting five-coordinate Zn centres have a coordination geometry intermediate between trigonal bipyramidal and square pyramidal. The behaviour of the title complex in DMSO solution suggests that it is a suitable NMR probe for similar or isostructural complexes including other transition-metal ions. The diamagnetic nature of the complex is reflected in similar 1H and 13C NMR chemical shifts for the free ligand pca as for the Zn complex.

The heterometallic coordination compound [Cu(Lys)(phen)]2V4O12·4H2O (Lys is the amino acid lysine, C6H14N2O2, and phen is 1,10-phenanthroline, C12H8N2) lies across an inversion centre. Two [Cu(Lys)(phen)]2+ units coordinate to the cyclo-vanadate fragment and the formula unit is completed by four solvent water molecules. The lysine ligand is in the zwitterionic form and chelates the CuII atom via the α-NH2 and α-COO− donor groups, while the ∊-NH3 + group is involved in intramolecular hydrogen bonds with the central [V4O12]4− core and with solvent water molecules. In the crystal, N—H...O and O—H...O hydrogen bonds connect the components of the structure to form a three-dimensional network. The crystal structure is further stabilized by π–π interactions involving the phen ligands. The lysine group is disordered over two sets of sites with refined occupancies of 0.534 (11) and 0.466 (11).