Structural Diversity in a New Series of Halogenated Quinolyl Salicylaldimides-Based FeIII Complexes Showing Solid-State Halogen-Bonding/Halogen•••Halogen Interactions

A new series of tridentate N-8-quinolyl-salicylaldimine ligands, Hqsal-5,7-X-2 [X = Cl(1), Br(2), I(3)] halosubstituted at the 5,7 position of the aminoquinoline moiety and their corresponding complexes with Fe in were synthesized and formulated as [Fe(qsal-5,7-X-2)(NCS)(MeO)](2)center dot solv. (X = Cl (1a), Br (2a), I (3a, solv = 1/2 MeOH), [Fe-4 (qsal-5,7-X-2)(4) (NCS)(2)(-)(MeO)(2)]center dot solv. (X = Br (2b), I (3b; solv = 4CH(2)Cl(2))) by single-crystal X-ray diffraction analysis. la and 2a are isostructural dimers where each Fe in metal ion, showing a distorted octahedral environment, is bound by a N,N,O tridentate (qsal-5,7-X-2)(-) (X = Cl and Br) ligand, a N-coordinated SCN- anion, and a bridging methanolate anion. 2b and 3b are centrosymmetric tetramers where each Fe m is bound by three nitrogen atoms and three oxygen atoms derived from a tridentate (qsal-5,7-X-2)(-) (X = Br and I), a SCN-, a bridging methanolate anion, and a bridging mu(2) - oxy moiety. In 3b, the iodine atoms dominate the packing interactions through the establishment of a halogen-bonding network. The magnetic behavior of 1a-3a dimers and 2b-3b tetramers indicate the presence of strong antiferromagnetic interactions between Fe in centers (S = 5/2), mediated by the alkoxy bridges. Experimental data can be modeled with an isotropic Hamiltonian, H = -2J(S-1 . S-2) for dimers U = -15 cm(-1)) and H = -2J(S-2 . S-3) - 2j'(S-1 . S-2 + S-3 . S-4), for tetramers (J = -24 cm(-1), = -11 cm(-1)). The magnetic behavior of 1a-3a dimers indicates the presence of strong antiferromagnetic interactions between Fe-III in centers (S = 5/2), mediated by the alkoxy bridges. 2b and 3b show the same magnetic behavior since they contains analogous bridges between paramagnetic centers, but for a linear tetramer. Density functional theory (DFT) calculations, based on hybrid functional mPW1PW paralleled by the Def2SVP all-electron split-valence basis sets, support the experimental results, showing that monomers could possibly show a spin crossover (SCO) behavior, even though the formation of complexes with an even number of metal ions results in the strong antiferromagnetic interactions. Accordingly, broken symmetry DFT calculations carried out on la clearly show that the antiferromagnetic coupling of the two HS Fe-III centers results in the lowest energy electron configuration of the complex.