A cyano and end-to-end azido bridged 3D copper(ii)–copper(i) mixed-valence coordination polymer and its transformation to copper nitride nanoparticles

Syntheses and characterization of a CN and end-to-end N₃ bridged three-dimensional Cu(II)–Cu(I) mixed valence polymer (1), with Cu-N₃ system without CN (2) and a CN-bridged Cu analogue without N₃ (3) are reported and solid-state transformation of the 1 to copper nitride nanoparticles performed.

Effect of phenylacetic acid coligands on the structures and magnetic properties of azido-bridged copper(ii)-chain compounds

To investigate how the structures and magnetic properties of azido–copper(ii) chain compounds are influenced by substituents on the phenylacetic acid coligands, three new azido-bridged Cu(ii) compounds have been successfully obtained, and structurally and magnetically characterized.

Role of dicarboxylate linkers in Mn(III)-salicylaldoximate based extended structures: synthesis, structures, and magnetic behavior

Four new oxo-centered Mn(III)-salicylaldoximate triangle-based extended complexes [Mn(III)6O2(salox)6(EtOH)4(phda)]n·(saloxH2)n·(2H2O)n (1), [Mn(III)6O2(salox)6(MeOH)5(5-I-isoph)]n·(3MeOH)n (2), [Mn(III)6O2(salox)6(MeOH)4(H2O) (5-N3-isoph)]n·(4MeOH)n (3) and [Mn(III)3NaO(salox)3(MeOH)4(5-NO2-isoph)]n·(MeOH)n (H2O)n (4) [salox=salicylaldoximate, phda=1,3-phenylenediacetate, isoph=isophthalate] have been synthesized under similar reaction conditions. Single crystal X-ray structures show that in 1, only one type of Mn6 cluster is arranged in 1D, whereas in 2 and 3 there are two types of clusters, differing in the way the triangle units are joined and assembled. In complex 4, however, the basic building structure is heteronuclear and based on Mn3 units extended in 2D. Susceptibility measurements (dc and ac) over a wide range of temperatures and fields show that the complexes 1, 2, and 3 behave as single molecule magnets (SMMs) with S=4 ground state, while 4 is dominantly antiferromagnetic with a ground spin state S=2. Density functional theory calculations have been performed on model complexes to provide a qualitative theoretical interpretation for their overall magnetic behavior.

Versatility of azide in serendipitous assembly of copper(II) magnetic polyclusters

Engineering at the molecular level is one of the most exciting new developments for the generation of functional materials. However, the concept of designing polynuclear extended structures from bottom up is still not mature. Although progress has been made with secondary building units (SBUs) in metal organic frameworks (MOFs), the control seems to be just an illusion when it comes to bridging ligands such as the azide ion. When we say that the azido ligand is versatile in its bridging capabilities, what we mean is that it would be difficult to predict or control its bridging properties. However, this kind of serendipity is not always bad news. For example, scientists have shown that the azido ligand can mediate magnetic exchanges between paramagnetic metals in a predictable fashion (usually depending upon the bonding geometries). Therefore, it is a well-respected ligand in polynuclear assemblies. Serendipitous assemblies offer new magnetic structures that we may not otherwise even think about synthesizing. The azido ligand forms a variety of complexes with copper(II) using different blocking amines or pyridine based ligands. Its structural nature changes upon changing the substitution on amine, as well as the amount of blocking ligand. In principle, if we take any of these complexes and provide more coordination sites to the bridging azido ligands by removing a fraction of the blocking ligands, we can get new complexes with intricate structural networks and therefore different magnetic properties with the same components as used for the parent complex. In this Account, we mainly discuss the development of a number of new topological and magnetic exchange systems synthesized using this concept. Not all of these new complexes can be grouped according to their basic building structures or even by the ratio of the metal to blocking ligand. Therefore, we divided the discussion by the nuclearity of the basic building structures. Some of the complexes with the same nuclearities have very similar or even almost identical basic structures. However, the way these building units are joined together (by the azido bridges) to form the overall extended structures differ almost in every case. The complexes having the Cu6 core are particularly interesting from a structural point of view. Although they have almost identical basic structures, some of them are extended in three dimensions, but two of them are extended in two dimensions by two different bridging networks. In the complexes having linear Cu4 basic units, we find that using similar ligands does not always give the same bridging networks even within the basic building structures. These complexes have also enriched the field of molecular magnetism. One of the complexes with a Cu3 building unit has provided us with the opportunity to study the competing behavior of two different kinds of magnetic exchange mechanism (ferromagnetic and antiferromagnetic) acting simultaneously between two metal ions. Through density functional theory calculations, we showed how they work independently and their additive nature to produce the overall effect. The exciting methodology for the generation of copper(II) polyclusters presented in this Account will provide the opportunity to explore analogous serendipitous assembly of diverse structures with interesting magnetic behavior using other transition metal ions having more than one unpaired electrons.