Chemically Separable Co(II) Spin-State Isomers.

The phenomenon of spin crossover involves coordination complexes with switchable spin states. This spin state change is accompanied by significant geometric changes such that low and high spin forms of a complex are distinct isomers that exist in equilibrium with one another. Typically, spin-state isomers interconvert rapidly and are similar enough in polarity to prevent their independent separation and isolation.

Metal-Metal Bond in Heterometallic Extended Metal Atom Chains.

Understanding the fundamental properties governing metal-metal interactions is crucial to understanding the electronic structure and thereby applications of multimetallic systems in catalysis, material science, and magnetism. One such property that is relatively underexplored within multimetallic systems is metal-metal bond polarity, parameterized by the electronegativities (χ) of the metal atoms involved in the bond. In heterobimetallic systems, metal-metal bond polarity is a function of the donor-acceptor (Δχ) interactions of the two bonded metal atoms, with electropositive early transition metals acting as electron acceptors and electronegative late transition metals acting as electron donors.

Paramagnetic Metal-Metal Bonded Heterometallic Complexes.

Significant progress has been made in the past 10-15 years on the design, synthesis, and properties of multimetallic coordination complexes with heterometallic metal-metal bonds that are paramagnetic. Several general classes have been explored including heterobimetallic compounds, heterotrimetallic compounds of either linear or triangular geometry, discrete molecular compounds containing a linear array of more than three metal atoms, and coordination polymers with a heterometallic metal-metal bonded backbone. We focus in this Review on the synthetic methods employed to access these compounds, their structural features, magnetic properties, and electronic structure.

Facile Axial Ligand Substitution in Linear Mo≣Mo-Ni Complexes.

Clean axial ligand substitution reactions of heterometallic extended metal atom chains (HEMACs) supported by the dpa ligand (dpa = 2,2'-dipyridylamine) have been synthetically challenging due to side reactions that alter the trimetallic core. Following the hypothesis that a heterometallic core containing second-row transition metals would be more robust toward ligand substitution, we report the synthesis of three new heterotrimetallic compounds, MoNi(dpa)(OTf) (1), MoNi(dpa)(NCS) (2), and MoNi(dpa)(NCSe) (3) that are obtained cleanly and in good yield. Compound 1 may be synthesized either directly by reaction of Ni(OTf) with Mo(dpa) (4) or indirectly, by reaction of MoNi(dpa)Cl (5) with 2 equiv of TlOTf.

Extraordinarily Large Ferromagnetic Coupling (J≥150 cm ) by Electron Delocalization in a Heterometallic Mo≣Mo-Ni Chain Complex.

The new heterometallic chain compounds Mo Ni(dpa) Cl (1) and [Mo Ni(dpa) Cl ]OTf (2) (dpa=2,2'-dipyridylamine) have been prepared and studied by crystallography and magnetic susceptibility, among other methods. Oxidation of 1 to 2 removes an electron from the multiply bonded Mo unit, consistent with the formulation of 2 containing a (Mo ) ⋅⋅⋅(Ni) core. While 1 contains an S=1, pseudo-octahedral Ni ion, 2 has an S=3/2 ground state, in which the two Ni unpaired electrons, one in a localized δ-orbital and one in a heavily delocalized σ -orbital are joined by an unpaired electron in a Mo-Mo δ-orbital.