A New Generation of Metal String Complexes: Structure, Magnetism, Spectroscopy, Theoretical Analysis, and Single Molecular Conductance of an Unusual Mixed‐Valence Linear [Ni₅]⁸⁺ Complex

Abstract

Two new linear pentanickel complexes [Ni5(bna)4(Cl)2][PF6]2 (1) and [Ni5(bna)4(Cl)2][PF6]4 (2; bna=binaphthyridylamide), were synthesized and structurally characterized. A derivative of 1, [Ni5(bna)4(NCS)2][NCS]2 (3), was also isolated for the purpose of the conductance experiments carried out in comparison with [Ni5(tpda)4(NCS)2] (4; tpda=tripyridyldiamide). The metal framework of complex 2 is a standard [Ni5]10+ core, isoelectronic with that of [Ni5(tpda)4Cl2] (5). Also as in 5, complex 2 has an antiferromagnetic ground state (J=-15.86 cm(-1)) resulting from a coupling between the terminal nickel atoms, both in high-spin sate (S=1). Complex 1 displays the first characterized linear nickel framework in which the usual sequence of NiII atoms has been reduced by two electrons. Each dinickel unit attached to the naphthyridyl moieties is assumed to undergo a one-electron reduction, whereas the central nickel formally remains NiII. DFT calculations suggest that the metal framework of the mixed-valence complex 1 should be described as intermediate between a localized picture corresponding to NiII-NiI-NiII-NiI-NiII and a fully delocalized model represented as (Ni2)3+-NiII-(Ni2)3+. Assuming the latter model, the ground state of 1 results from an antiferromagnetic coupling (J=-34.03 cm(-1)) between the two (Ni2)3+ fragments, considered each as a single magnetic centre (S=3/2). An intervalence charge-transfer band is observed in the NIR spectrum of 1 at 1186 nm, suggesting, in accordance with DFT calculations, that 1 should be assigned to Robin-Day class II of mixed-valent complexes. Scanning tunnelling microscopy (STM) methodology was used to assess the conductance of single molecules of 3 and 4. Compound 3 was found approximately 40% more conductive than 4, a result that could be assigned to the electron mobility induced by mixed-valency in the naphthyridyl fragments.

Two Linear Undecanickel Mixed‐Valence Complexes: Increasing the Size and the Scope of the Electronic Properties of Nickel Metal Strings

“…As proposed in a previous study, [8] the extra electron was initially accommodated in the d x 2 Ày 2 orbital of squareplanar nickel centers Ni2 or Ni10. This reduction step induced a partial transfer to the d z 2 orbital of pyramidal nickel centers Ni1 or Ni11 through the s antibonding fragment orbital, leading to a spin state S = 3/2 for the Ni 2 3+ unit.…”

“…[5] Using this strategy, [6] we obtained a series of stable, low-oxidation-state-nickel string complexes combining mixed-valency, a property important in the development of novel electronic materials, [7] with an enhanced electron mobility, which is able to increase the conductance of molecular metal wires. [8] We report a new tetranaphthyridyltriamine ligand,…”

Construction of a Planar Tetrapalladium Cluster by the Reaction of Palladium(0) Bis(isocyanide) with Cyclic Tetrasilane

“…To overcome these drawbacks, a new methodology called template synthesis has recently been introduced [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. In this method, the products are synthesized by clustering multiple metal atoms To overcome these drawbacks, a new methodology called template synthesis has recently been introduced [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

“…In this method, the products are synthesized by clustering multiple metal atoms To overcome these drawbacks, a new methodology called template synthesis has recently been introduced [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. In this method, the products are synthesized by clustering multiple metal atoms on the template.…”

“…The structure of the clusters obtained in this method is highly controllable by using template molecules with appropriate structures; the yield of the product is generally high. Using this synthetic strategy, many transition metal clusters having 1D chain-like structures have been prepared by employing polyenes [10][11][12][13], multidentate phosphines [14][15][16][17], and nitrogen-containing compounds as templates [18][19][20][21][22]. Similarly, the use of (poly)cyclic aromatic hydrocarbons as a template led to the formation of metal clusters with 2D sheet-like structures [23][24][25][26][27][28].…”