Intermolecular antiferromagnetism is a type of magnetic behaviour in which the magnetic moments associated with metal atoms or ions belonging to neighbouring molecules become aligned in opposite directions. As a result, the magnetic moments tend to cancel each other, producing a low net magnetic moment. This phenomenon arises from exchange interactions between unpaired electrons of neighbouring paramagnetic centres. The interaction may occur through direct metal–metal contact or through intervening atoms or ligands. A suitable example is provided by compounds containing pairs of metal centres with partially filled (d)-orbitals. In a system containing two neighbouring metal ions, each having one or more unpaired electrons, the magnetic moments can arrange themselves either parallel or antiparallel. If the antiparallel arrangement has lower energy, the compound exhibits antiferromagnetism. The simplest illustration can be represented as [ M^{n+}; \uparrow \qquad M^{n+}; \downarrow ] where the arrows represent the spins of unpaired electrons on neighbouring metal centres. In contrast, a ferromagnetic arrangement would be [ M^{n+}; \uparrow \qquad M^{n+}; \uparrow ] In antiferromagnetic substances,