Chemisorption of Exchange‐Coupled [Ni₂L(dppba)]⁺ Complexes on Gold by Using Ambidentate 4‐(Diphenylphosphino)benzoate Co‐Ligands

Abstract

A new strategy for the fixation of redox-active dinickel(II) complexes with high-spin ground states to gold surfaces was developed. The dinickel(II) complex [Ni2L(Cl)]ClO4 (1ClO4), in which L(2-) represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, reacts with ambidentate 4-(diphenylphosphino)benzoate (dppba) to form the carboxylato-bridged complex [Ni2L(dppba)](+), which can be isolated as an air-stable perchlorate [Ni2L(dppba)]ClO4 (2ClO4) or tetraphenylborate [Ni2L(dppba)]BPh4 (2BPh4) salt. The auration of 2ClO4 was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni(II)2Au(I) complex [Ni(II)2L(dppba)Au(I)Cl]ClO4 (3ClO4). Metathesis of 3ClO4 with NaBPh4 produces [Ni(II)2L(dppba)Au(I)Ph]BPh4 (4BPh4), in which the Cl(-) is replaced by a Ph(-) group. The complexes were fully characterized by ESI mass spectrometry, IR and UV/Vis spectroscopy, X-ray crystallography (2BPh4 and 4BPh4), cyclic voltammetry, SQUID magnetometry and HF-ESR spectroscopy. Temperature-dependent magnetic susceptibility measurements reveal a ferromagnetic coupling J = +15.9 and +17.9 cm(-1) between the two Ni(II) ions in 2ClO4 and 4BPh4 (H = -2 JS1S2). HF-ESR measurements yield a negative axial magnetic anisotropy (D<0), which implies a bistable (easy axis) magnetic ground state. The binding of the [Ni2L(dppba)]ClO4 complex to gold was ascertained by four complementary surface analytical methods: contact angle measurements, atomic-force microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. The results indicate that the complexes are attached to the Au surface through coordinative Au-P bonds in a monolayer.

Synthesis and Characterization of Pentanuclear Complexes Composed of Pairs of Macrocyclic Ni2L and Zn2L Complexes Linked by cis‐[PtCl2(dppba)2] and trans‐[RhCl(CO)(dppba)2] [dppba = (4‐Diphenylphosphanyl)benzoate, L = Macrocyclic Ligand]

“…[2] Further support comes from the electronic absorption bands at 651 and 1121 nm attributable to spin-allowed ν 2 and ν 1 transitions of a six-coordinate NiN 3 S 2 O carboxylate chromophore. The IR and UV/Vis data closely compare with those of the known [(Ni 2 L)(μ-dppba)] + complex 2, [10] showing that coordination of the Pt 2+ ion to the dppba ligand has little (if any) influence on the spectroscopic properties of the [Ni 2 L] 2+ entity.…”

“…[10] The aim of the presented work was to examine whether pentanuclear complexes are accessible. 2 ] via replacement of the platinum bound acetonitrile ligands followed by precipitation with LiClO 4 .…”

“…[8,9] ARTICLE They have also been utilized for the immobilization of paramagnetic transition metal complexes to metal surfaces. [10] We have already shown that dppba can be used to form trinuclear Ni 2 Au complexes in a sequential fashion as illustrated in Scheme 1. Thus, complex [Ni 2 L(μ-Cl)] + (1) reacts in a first step with the carboxylate group of the dppba anion by replacement of the bridging chloride to form the carboxylato complex [Ni 2 L(μ-dppba)]…”

Synthesis and Characterisation of Luminescent [CrIII2L(μ‐carboxylato)]3+ Complexes with High‐Spin S=3 Ground States (L=N6S2 donor ligand)

“…The doubly deprotonated form, L 2− , is an effective dinucleating ligand that readily forms bioctahedral complexes of the type [M 2 L( μ ‐L′)] + with various first‐row transition metal ions (M=Mn 2+ , Fe 2+ , Co 2+ , Co 3+ , Ni 2+ , Figure 1 ). [38] Several co‐ligands such as L′=Cl − , OH − , [39] HS − , [40] and RCO 2 − ,[ 41 , 42 , 43 , 44 , 45 , 46 ] to name just a few, can be accommodated between the divalent metal ions. Complexes of this kind offer the opportunity to investigate intramolecular magnetic super‐exchange interaction as a function of the electronic configuration of the metal ions and the type of the coligand.…”

Deposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands

“…The ambidentate phosphane-carboxylato [ 38 ] and thiol-carboxylato coligands H 2 L 2 and H 1 L 3 ( Fig. 1 ) were found to bind selectively via their carboxylate function to form the carboxylato-bridged complexes [Ni 2 L(HL 2 )](ClO 4 ) ( 2 ) and [Ni 2 L(L 3 )](ClO 4 ) ( 3 ) [ 39 – 40 ] such that an exposed thiol or phosphane group is available for further functionalization. Indeed, 2 dimerizes via a disulphide bond upon oxidation in air to generate a tetranuclear [{Ni 2 L} 2 (O 2 CC 6 H 4 S) 2 ] 2+ complex, while “auration” of 2 and 3 with Au I sources leads to the trinuclear Ni II 2 Au I species 4 and 5 .…”