Chemisorption of Exchange-Coupled [Ni sub(2)L(dppba)] super(+) Complexes on Gold by Using Ambidentate 4-(Diphenylphosphino)benzoate Co-Ligands

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 [Ni sub(2)L(Cl)]ClO sub(4) (1ClO sub(4)), in which L super(2-) represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, reacts with ambidentate 4-(diphenylphosphino)benzoate (dppba) to form the carboxylato-bridged complex [Ni sub(2)L(dppba)] super(+), which can be isolated as an air-stable perchlorate [Ni sub(2)L(dppba)]ClO sub(4) (2ClO sub(4)) or tetraphenylborate [Ni sub(2)L(dppba)]BPh sub(4) (2BPh sub(4)) salt. The auration of 2ClO sub(4) was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni super(II) sub(2)Au super(I) complex [Ni super(II) sub(2)L(dppba)Au super(I)Cl]ClO sub(4) (3ClO sub(4)). Metathesis of 3ClO sub(4) with NaBPh sub(4) produces [Ni super(II) sub(2)L(dppba)Au super(I)Ph]BPh sub(4) (4BPh sub(4)), in which the Cl super(-) is replaced by a Ph super(-) group. The complexes were fully characterized by ESI mass spectrometry, IR and UV/Vis spectroscopy, X-ray crystallography (2BPh sub(4) and 4BPh sub(4)), cyclic voltammetry, SQUID magnetometry and HF-ESR spectroscopy. Temperature-dependent magnetic susceptibility measurements reveal a ferromagnetic coupling J=+15.9and +17.9cm super(-1) between the two Ni super(II) ions in 2ClO sub(4) and 4BPh sub(4) (H=-2JS sub(1)S sub( 2)). HF-ESR measurements yield a negative axial magnetic anisotropy (D