Chemisorption of Exchange‐Coupled [Ni2L(dppba)]+ 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 [Ni₂L(Cl)]ClO₄ ( 1 ClO₄), 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 ( 2 ClO₄) or tetraphenylborate [Ni₂L(dppba)]BPh₄ ( 2 BPh₄) salt. The auration of 2 ClO₄ was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni^II₂Au^I complex [Ni^II₂L(dppba)Au^ICl]ClO₄ ( 3 ClO₄). Metathesis of 3 ClO₄ with NaBPh₄ produces [Ni^II₂L(dppba)Au^IPh]BPh₄ ( 4 BPh₄), 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 ( 2 BPh₄ and 4 BPh₄), 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 2 ClO₄ and 4 BPh₄ (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.