Hexacyanometalate Molecular Chemistry: Di‐, Tri‐, Tetra‐, Hexa‐ and Heptanuclear Heterobimetallic Complexes; Control of Nuclearity and Structural Anisotropy

Abstract

Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)(6)](3-) cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)(n)(CN-M'L)(6-n)](m+) (with n=0-5; M=Cr(III), Co(III), M'=Ni(II); L=pentadentate ligand). Thus, with M=Cr(III), d(3), S=3/2, a dinuclear complex [Cr(III)(CN)(5)(CN-NiL(n))](9+), (L(n)=polydentate ligand) was built and characterised, showing a spin ground state, S(G)=5/2, with a ferromagnetic interaction J(Cr,Cu)=+18.5 cm(-1). With M=Co(III) (d(6), S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi(2), CoNi(3), CoNi(5) and CoNi(6). By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.

Unusual Magnetic Metal–Cyanide Cubes of ReII with Alternating Octahedral and Tetrahedral Corners

“…Chemie interactions [9] did not entirely reproduce the gradual slope of c m T, but the data are reproducible for pure batches of crystals, thereby ruling out the presence of impurities. Further efforts are underway to develop a model for this system that accounts for the behavior of 1 over the entire temperature range.…”

Photomagnetic Effects in Polycyanometallate Compounds: An Intriguing Future Chemically Based Technology?

“…Molecules containing up to six paramagnetic metal ions coordinated to a polycyanometallate anion have been isolated. [39] If such compounds are highly anisotropic, these molecules may behave as photochromic single-molecule magnets (SMMs). [40] The way for obtaining this kind of system has been recently traced by Marvaud, MathoniØre, and co-workers.…”

Synthesis and Redox‐Induced Structural Isomerization of the Pentagonal Bipyramidal Complexes [W(CN)5(CO)2]3− and [W(CN)5(CO)2]2−

“…As evident from the HOMO depictions in Figure 3, the driving force for the oxidationinduced ligand isomerization can be traced to a preference for the less-electron-rich W III center to engage in extensive p backbonding with just one rather than two axial CO ligands. The isomerization of this low-spin d 3 complex can further be viewed as a Jahn-Teller distortion associated with the loss in degeneracy of the pair of e 1 '' orbitals to give a fully occupied 1a 1 '' orbital 0.003 eV below a half-occupied 2a 1 '' orbital. This loss of orbital degeneracy may also account for the anisotropy of the g tensor observed by EPR spectroscopy being less than anticipated.…”

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There has been a surge of interest in the use of cyanometalate complexes for the synthesis of magnetic molecules [1] and solids.[2] The variation of the metal electron configuration and coordination geometry enables adjustment of magnetic properties, such as the spin ground state, magnetic anisotropy, and the strength of the exchange coupling. Second-and thirdrow transition-metal ions are of particular interest, owing to a large magnetic anisotropy stemming from spin-orbit coupling, as well as to their diffuse valence d orbitals, which can result in strong magnetic exchange.

[3] Owing to poorly understood reactivity patterns and the preference for low-spin electron configurations, however, there are relatively few examples of simple, paramagnetic building units containing these metals.

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