Realization of Unusual Ligand Binding Motifs in Metalated Container Molecules: Synthesis, Structures, and Magnetic Properties of the Complexes [(LMe)Ni2(μ‐L′)]n+ with L′=NO3−, NO2−, N3−, N2H4, Pyridazine, Phthalazine, Pyrazolate, and Benzoate

Abstract

A series of dinickel(II) complexes with the 24-membered macrocyclic hexaazadithiophenol ligand H₂L^Me was prepared and examined. The doubly deprotonated form (L^Me)²⁻ forms complexes of the type [(L^Me)Ni (μ-L′)]ⁿ⁺ with a bioctahedral N₃Ni^II(μ-SR)₂(μ-L′)Ni^IIN₃ core and an overall calixarene-like structure. The bridging coordination site L′ is accessible for a wide range of exogenous coligands. In this study L′=NO₃⁻, NO₂⁻, N₃⁻, N₂H₄, pyrazolate (pz), pyridazine (pydz), phthalazine (phtz), and benzoate (OBz). Crystallographic studies reveal that each substrate binds in a distinct fashion to the [(L^Me)Ni₂]²⁺ portion: NO₂⁻, N₂H₄, pz, pydz, and phtz form μ_1,2-bridges, whereas NO₃⁻, N₃⁻, and OBz⁻ are μ_1,3-bridging. These distinctive binding motifs and the fact that some of the coligands adopt unusual conformations is discussed in terms of complementary host–guest interactions and the size and form of the binding pocket of the [(L^Me)Ni₂]²⁺ fragment. UV/Vis and electrochemical studies reveal that the solid-state structures are retained in the solution state. The relative stabilities of the complexes indicate that the [(L^Me)Ni₂]²⁺ fragment binds anionic coligands preferentially over neutral ones and strong-field ligands over weak-field ligands. Secondary van der Waals interactions also contribute to the stability of the complexes. Intramolecular ferromagnetic exchange interactions are present in the nitrito-, pyridazine-, and the benzoato-bridged complexes where J=+6.7, +3.5, and +5.8 cm⁻¹ (H=−2 JS₁S₂, S₁=S₂=1) as indicated by magnetic susceptibility data taken from 300 to 2 K. In contrast, the azido bridge in [(L^Me)Ni₂(μ_1,3-N₃)]⁺ results in an antiferromagnetic exchange interaction J=−46.7 cm⁻¹. An explanation for this difference is qualitatively discussed in terms of bonding differences.