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 [Mn^II Mn^III Mn^IV(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.

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 Cu^II 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).

The new diamagnetic complex, [Zn₂(N₃)₄(C₆H₆N₂O)₂] or [Zn₂(pca)₂(μ_1,1-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.

In this study, the synthesis and characterization of three Cu­(II) complexes employing the Schiff base ligand 2-[(2-hydroxy-benzylidene)-amino]-2-hydroxymethylpropane-1,3-diol (H₄L), sodium azide (NaN₃), and Cu­(II) salts were investigated. This research led to the formation of [Cu₄(H₂L)₄(H₂O)] 1, previously reported, the first octa-nuclear cubane-like compound based on the {Cu₄O₃N} core, [Cu₄(μ₃-N₃)­(H₂L)₂(HL)­(H₂O)]₂ 2, and a polymeric compound [Cu₃(H₂L)₂(μ₂-N₃)₂]_n 3. Single-crystal X-ray diffraction analysis revealed that 1·CH₃OH possesses a ‘4 + 2’ cubane-type core, 2 is a double cubane of eight Cu­(II) ions including μ₃-alkoxido and μ₃-azido bridges, while 3 is a polymeric structure with three Cu­(II) ions conforming the monomeric unit. Temperature-dependent (2.9–300 K) magnetic susceptibility measurements demonstrate the coexistence of ferromagnetic and antiferromagnetic spin exchange interactions in 1, associated with Cu–O–Cu bridging angles ranging from 77.81(6)° to 112.77(8)°. Compounds 2 and 3 exhibited antiferromagnetic exchange coupling, attributed to their large Cu–O–Cu bond angles, the largest of which was 108.92°. The ESR spectra of 1–3 at 300 and 90 K are axial, accompanied by hyperfine splitting in g _∥ and coupling constants A _Cu in the range 169 × 10^–4 cm^–1 to 197 × 10^–4 cm^–1. In accordance with g _⊥ values >2.0023, the unpaired electron ground state is dx2−y2 , consistent with a Cu­(II) ion. Furthermore, for 2, a forbidden half-field transition was observed, which is characteristic of ΔM _S = ± 2 for antiferromagnetic exchange interaction of dimers of Cu­(II). These affirmations align with the ESR spectra area ratio and line width as the temperature decreases. The IR, absorption spectra, and magnetic studies of 1–3 were analyzed and compared to those of analogous complexes with the same geometry.

In this work we report the synthesis, structural, electronic and magnetic characterization of [Mn^IV₂Mn^II₂(HL)₂(H₂L)₂(H₂O)₄](NO₃)₂ 1. This novel compound was obtained from (E)-2-((2-hydroxybenzylidene)amine)-2-(hydroximethyl-propane-1,3-diol, (H₄L) and Mn(NO₃)₂. The UV-Vis and IR spectrophotometry showed the typical d-d transitions of Mn^IV in and octahedral geometry compounds ¹ and vibrational transitions in 477 cm^-1, which is assigned to the Mn-O group ². The c_M vs T gave J = 164 cm^{-1 3}. The ESR (g = 11.03, 4.87, 1.78, and g = 3.23, 2.03) analysis of 1 showed the presence of Mn^II (s = 5/2) and Mn^IV (s = 3/2) ions within the molecule. The hyperfine interaction is observed in ESR spectrum which showed two species of Mn ions⁴. An x ray diffraction suitable monocristal of 1 was obtained and its structure was possible to describe as a tetramer of [Mn^IV Mn^II Mn^II Mn^IV] building a 2D stepped supramolecular structure with a step of [Mn^IV–O-O-Mn^II] and a second step with [Mn^II–O-O-Mn^IV]. The structural study informed us that each magnetic box of [Mn^IV-O-O-Mn^II] have a superexchange antiferromagnetic interaction by the d_x2_-y2-sp³ (with more contribution of p orbitals) orbitals; however, among the boxes or steps there is a super-exchange ferromagnetic interaction, by oxo bonds Mn^II-O-Mn^II. Ye T., Li S., Wu X., Xu M., Wei X., Wang K., Bao H., Wang J. and Chen J. J. Mater. Chem. C, 2013, 1, 4327–4333. Lever A. B. P. Inorganic Electronic Spectroscopy. 2a Edition. Elsevier, 1997. Czernuszewicz S. R., Su O. Y., Stern K. M., Macor A. K., Kim D., Groves T. J. and Spiro G. T. Am. Chem. Soc. 1988, 110, 4158-4165. Nakamoto K. Infrared and Raman Spectra of Inorganic and Coordination Compounds. 6a edition, John Wiley & Sons, 2009. Yoo J., Brechin E., Yamaguchi A., Nakano M., Huffman C. J., Maniero L. A., Brunel L. C., Awaga K., Ishimoto H., Christou G. y Hendrickson D. Chem. 2000, 39, 3615-3623. Milios J. C., Piligkos S., Bell R. A., Laye H. R., Teat J. S., Vicente R., McInnes E., Escuer A., Perlepes P. S. y Winpenny P. E. R. Inorganic Chemistry Communications. 2006, 9, 638–641. Ramírez R. D., Zamorano U. R., Pérez M. O. Solid State Communications. 2001, 118, 371-376.