title: 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.
authors.affiliation: Institut für Anorganische Chemie, Universität Leipzig, 04103 Leipzig, Germany.
authors.forename: Matthias
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authors.lastname: Golecki
authors.forename: Jochen
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authors.lastname: Lach
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authors.lastname: Jeremies
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authors.lastname: Lungwitz
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authors.lastname: Fronk
authors.forename: Georgeta
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authors.lastname: Salvan
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authors.initials: DR
authors.lastname: Zahn
authors.forename: Jaena
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authors.forename: Yulia
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authors.lastname: Krupskaya
authors.forename: Vladislav
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authors.lastname: Kataev
authors.forename: Rüdiger
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authors.lastname: Klingeler
authors.forename: Bernd
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authors.lastname: Büchner
authors.forename: Benjamin
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authors.lastname: Mahns
authors.forename: Martin
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authors.lastname: Knupfer
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authors.lastname: Siles
authors.forename: Daniel
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authors.lastname: Grimm
authors.forename: Oliver G
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authors.lastname: Schmidt
authors.forename: Andreas
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authors.lastname: Reis
authors.forename: Werner R
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authors.lastname: Thiel
authors.forename: Daniel
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authors.lastname: Breite
authors.forename: Bernd
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authors.lastname: Abel
authors.forename: Berthold
authors.initials: B
authors.lastname: Kersting