Theoretical Studies on the Structures of Metal String Complexes Cr_n(L)₄Cl₂ (n = 3, 5, 7; L = Oligo-α-Pyridylamide) under the Effect of an Electric Field

Abstract

To study the electronic structures and properties of [Cr n (L) 4 Cl 2 ] (n = 3, L = dpa: di(2-pyridyl)amido; n = 5, L = tpda: tripyridyldiamido; n = 7, L = teptra: tetrapyridyltriamine) metal string complexes, the BP86 method was used by considering the influence of the electric field (EF) applied parallel to the metal axis. As the EF increases, the migration of more positively charged Cr odd is more significant than that of Cr even , which results in alternating long−short Cr−Cr bonds. This happens because of the natural charges on the Cr odd of 1−3, which are more electropositive than those on Cr even . The electrons are pulled to the Cr and Cl(r) atoms at the high-potential side from Cl(l) at the low-potential side by the EF, which leads to asymmetrical FMOs. After the critical electric field (E c ), the configuration turns into a remarkably asymmetric one with alternating Cr−Cr quadruple bonds and weak interactions. The electrons are transferred from equatorial ligands (L) to metal chains. In the meantime, the asymmetry of the FMOs increases and the delocalization is further reduced, which affects the conductivity. Especially for [Cr 7 (teptra) 4 Cl 2 ], the delocalized electrons of HOMO are completely transformed into a localized model after the critical electric field. It is observed that this supports the electric switching phenomenon ascribed to the conformations of delocalized and localized electrons. In addition, the longer the length of the metal chain, the smaller the E c and the easier is for the complexes to be polarized by the EF.

The structure of a pentachromium(II) extended metal atom chain at 3 K: Cotton’s conjecture proven

“…The longer heptachromium(II) congener of 1 19 as well as penta-, 20 hepta-, 21 and nonachromium 22 species with pyrazinemodulated ligands showed similar features. This dual interpretation of X-ray data is presumably at the origin of the claimed existence of both symmetric and unsymmetric forms 12,23,24 to explain some electric and spectroscopic data. For instance, the bimodal singlemolecule conductance of 2 measured in break-junction experiments 12 was attributed to coexisting symmetric and unsymmetric isomers.…”

The structure of a pentachromium(ii) extended metal atom chain at 3 K: Cotton's conjecture proven

“…The longer heptachromium(II) congener of 1 19 as well as penta-, 20 hepta-, 21 and nonachromium 22 species with pyrazinemodulated ligands showed similar features. This dual interpretation of X-ray data is presumably at the origin of the claimed existence of both symmetric and unsymmetric forms 12,23,24 to explain some electric and spectroscopic data. For instance, the bimodal single-molecule conductance of 2 measured in break-junction experiments 12 was attributed to coexisting symmetric and unsymmetric isomers.…”

Structure and redox behaviour of a paramagnetic Rh–Pt–Cu–Pt–Rh heterometallic-extended metal-atom chain

“…Extended metal-atom chains (EMACs) comprising multiple metal ions connected by metal–metal bonds are useful platforms for nanometre-sized wires. 1–9 Synthetic efforts have been launched to fabricate heterometallic EMACs with two, three, and four different metals. 10–13 These materials exhibit unique physical properties, 14–16 which depend on the composition of the metal-atom backbone.…”