Molecular magnetic materials : design, synthesis and characterization

Abstract

Much attention has been devoted to increase dimensionality to one, two- and/or three-dimensional network complex systems with the aim of understanding the mechanism of magnetic interactions and enhancing bulk magnetic properties. In this connection, the bridging ligands which can mediate magnetic couplings between paramagnetic metal centers have played a crucial role in improvement of molecular structure. Our research is directed toward the use of three kinds of bridging ligands such as bpe (=1,2-bis(4-pyridyl)ethane), tp (=terephthalate) and azide. The treatment of Mn(II) ion with bpe ligand and dipotassium tp produced a novel three-dimensional complex, $[Mn(bpe)(H_{2}O)_{4}]_{n}(tp)_{n}(bpe)_{2n}$ ($bf{1}) whose solid-state structure is spread out via hydrogen bonds of packing bpe ligands and tp counter dianion. The use of sodium azide as another bridge instead of tp caused two dimensional sheet, $[Mn(bpe)(N_{3})_{2}]_{n}$ ($bf{4}) in which the azide group covalently links Mn(bpe) chain via end-to-end mode. A useful way to fabricate higher dimensional compounds is to use both one-dimensional polymers and additional bridging ligands. From this background a precursor compound was prepared by the reaction of Mn(II) ion with bpe (=1,2-bis(4-pyridyl)ethane) ligand, giving a one-dimensional bpe-bridged complex, $[Mn(bpe)(H_{2}O)_{4}]_{n}(ClO_{4})_{2n}(bpe)_{4n}(H_{2}O)_{n}$ ($bf{2}$) which has four water molecules around Mn(II) ion. To improve the molecular dimensionality, the treatment of this one-dimensional precursor with another bridging ligand, tp (=terephthalate) was attempted, affording a novel three-dimensional network, $[Mn(bpe)_{1.5}(tp)(H_{2}O)]_{n}(H_{2}O)_{n}$ ($bf{3}$) whose molecular structure reveals that tp ligands with two kinds of binding modes of unidentate and bridging form two-dimensional sheets which are linked via bpe ligands, leading to three-dimensional network. In order to explore the conformational availability of the long and flexible...