Remote Effects of Axial Ligand Substitution in Heterometallic Cr≡Cr···M Chains

Abstract

The heterometallic complexes CrCrM(dpa)(4)Cl(2) (dpa = 2,2'-dipyridylamide) featuring linear Cl-Cr≡Cr···M-Cl chains can regiospecifically be modified via axial ligand substitution to yield OTf-Cr≡Cr···M-Cl chains (OTf = triflate) with M being Fe, Mn, or Co. The effect of OTf substitution on the Cr side of the molecule has an unusual and profound structural impact on the square-pyramidal transition metal M. Specifically, elongation of the four equatorial M-N(py) bonds and the axial M-Cl bonds by 0.03 and 0.09 Å for Fe and 0.07 and 0.11 Å for Mn is observed. The longer M-Cl and M-N(py) bonds result from subtle interactions between the equatorial dpa ligand and the three metal ions. The equatorial dpa ligand responds to the introduction of the more labile OTf ligand at Cr by binding more strongly to this Cr ion which in turn weakens bonding to M. The ligand field experienced by M can be tuned by changing the Cr axial ligand, and this effect is observed in electrochemical measurements of the iron compounds.

Extraordinarily Large Ferromagnetic Coupling (J≥150 cm−1) by Electron Delocalization in a Heterometallic Mo≣Mo−Ni Chain Complex

“…Additionally, a recent report of unusually large single molecule conductance behavior of Mo≣Mo−Ni(npo) 4 (NCS) 2 (Hnpo=(1,8‐naphthyridin‐2(1 H )‐one) prompts an investigation into the electronic structures of Mo≣Mo−Ni chain compounds. Oxidation of M A ≣M A −M B HEMACS with M A =Mo has been proposed to remove an electron from the Mo 2 δ‐bonding orbital but until this report, we have been unable to stabilize such an oxidized complex . The only HEMACs that have been amenable to chemical oxidation have had a different type of electronic structure .…”

From Homonuclear Metal String Complexes to Heteronuclear Metal String Complexes

“…This remote influence is induced by a tilting of the dpa -ligands around their central amido nitrogen atoms in response to the variable ligand-field strength at the terminal Cr atom. [45] Scheme 9. The remote influence for the preparation of 41 and 42 in the work of Berry.…”

“…The remote influence for the preparation of 41 and 42 in the work of Berry. [45] [MoMoRu(dpa) 4 Cl 2 ] (44) and [WWRu(dpa) 4 Cl 2 ] (45) represent the first HMSCs that do not contain first-row transition metals. [46] Crystallographic studies reveal very short Mo-Ru and W-Ru distances of 2.38 and 2.39 Å, respectively, which suggest significant electron delocalization along the M-M-Ru chain.…”

A multiconfigurational approach to the electronic structure of trichromium extended metal atom chains

“…Otherwise an asymmetric structure is preferred, the most extreme examples being with very poor donors such as NO 3 − and BF 4 − . [24][25][26][27] Recent reports of heterometallic Cr 2 M EMACs (M = Mn, Fe, Co, Ni, Zn) from the laboratories of Berry [28][29][30][31][32] and Nuss 33 confirm that highly asymmetric structures containing a quadruply bonded Cr 2 unit weakly coupled to a third metal centre, are ubiquitous. This suggests that the symmetric structures of Cr 3 (dpa) 4 (CN) 2 and Cr 3 (dpa) 4 (CCR) 2 are the exception rather than the rule.…”

“…The latter can be used to tune the electronic properties of the chain, and, in the case of the cyanide and thiocyanate ligands, CN − and NCS − , attach the complex to metallic electrodes. Measurements of the electrical conductivity through the EMACs show a strong dependence on the identity of the metal, 22,[24][25][26][27][28][29][30][31][32] suggesting that metal-metal bonding may play an important role in controlling electron transport.…”