Structural and magnetic properties of heptacoordinated Mn-II complexes containing a 15-membered pyridine-based macrocycle and halido/pseudohalido axial coligands

摘要

A series of heptacoordinated Mn-II compounds with a pentadentate 15-membered pyridine-based macrocycle 15-pyN(3)O(2)(3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1(18),14,16-triene) and two axially coordinated halido/pseudohalido coligands (X), having a monomeric [Mn(15-pyN(3)O(2))X-2] (X = Br- (1), I- (2), N-3(-) (3), NCS- (4)) or polymeric {[Mn(15-pyN(3)O(2))X](ClO4)}(n) (X = CN- (5)) composition, was prepared and thoroughly characterized. Single crystal X-ray analysis of 2, 3 and 4 determined the distorted pentagonal-bipyramidal geometry of the complexes. The analysis of the magnetic data of complexes 1-4 revealed non-zero values of the axial zero-field splitting parameter D (vertical bar D vertical bar < 0.7 cm(-1)) and weak antiferromagnetic intermolecular interactions (molecular field correction parameter zj approximate to -0.1 cm(-1)). As for the 1D polymeric complex 5, a small antiferromagnetic exchange coupling was found between Mn-II centres, with J = -1.72 cm(-1). The experimentally obtained magnetic parameters (J or zj) were compared with those theoretically calculated at the DFT level in order to reveal the magnetic exchange pathways in 2-4 and to support the polymeric structure of 5 (J(EXP) = -2.79 cm(-1) vs. J(R)/J(Y) = -2.54/-3.06 cm(-1), when the dinuclear spin Hamiltonian was used). It has been also found that extensive systems of hydrogen bonds, non-covalent contacts and pi-pi stacking interactions present in the crystal structures of 2, 3 and 4 have an impact on the formation of supramolecular 1D chains, and as a consequence of this on the magnetic properties of the complexes. Contrary to non-covalent contacts, the influence of the axial ligands on the magnetic nature of the complexes seems to be negligible.