H-bonded supramolecular synthon induced magnetic superexchange phenomenon results weak ferromagnetic and strong antiferromagnetic interactions in two new copper-orotate coordination network

摘要

Hydrothermal self-assembly of orotic acid (C5H4N2O4=OrH(3)) with metal salt Cu(Ac)(2)center dot H2O yielded a new OrH based hydrogen bonded coordination network of formula [Cu(OrH)(2NH(3))(H2O)]center dot H2O (1) and [Cu (OrH) (2NH(3))](2) (2). Single crystal X-ray study on 1 confirms that +2 charges on the metal ions (Cu2+) are balanced by OrH anion. N-H center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonding synthons are the only artifact for the resulting hydrogen bonded copper-OrH architecture. Temperature dependent measurements of magnetic susceptibility reveals the occurrence of competitive exchange interactions with a net ferromagnetic character in 1 (J = +0.48 cm(-1)) and strong antiferromagnetic interaction in 2 (J = -4.93 cm(-1)). Magnetic superexchange interaction transmitted through equatorial-axial hydrogen bridge system promotes weak ferromagnetic interactions in 1 while in 2 it is in basal-basal position, in which two d(x2-y2)orbitals is involved in exchange mechanism reveals the coexistence of two antiferromagnetic exchange pathways, intramolecular much stronger than intermolecular. The natural bond orbital (NBO) analysis applied separately to alpha and beta spin density matrices clearly shows two important magnetic superexchange pathway with shorter Cu center dot center dot center dot Cu contact 5.542(4) angstrom and 4.845(4) angstrom or 5.755(1) angstrom in (1) and inter dimer 6.665(1) angstrom and 4.6744(9) angstrom for (2). (C) 2017 Elsevier Ltd. All rights reserved.