Mixed-Valence Tetrametallic Iridium Chains

Neutral [X-{Ir2 }-{Ir2 }-X] (X=Cl, Br, SCN, I) and dicationic [L-{Ir2 }-{Ir2 }-L]2+ (L=MeCN, Me2 CO) tetrametallic iridium chains made by connecting two dinuclear {Ir2 } units ({Ir2 }=[Ir2 (μ-OPy)2 (CO)4 ], OPy=2-pyridonate) by an iridium-iridium bond are described. The complexes exhibit fractional averaged oxidation states of +1.5 and electronic delocalization along the metallic chain. While the axial ligands do not significantly affect the metal-metal bond lengths, the metallic chain has a significant impact on the iridium-L/X bond distances. The complexes show free rotation around the unsupported iridium-iridium bond in solution, with a low-energy transition state for the chloride chain. The absorption spectra of these complexes show characteristic bands at 438-504 nm, which can be fine-tuned by varying the terminal capping ligands.

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

To study the electronic structures and properties of [Cr_n(L)₄Cl₂] (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 [Cr₇(teptra)₄Cl₂], 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.