Effects of Concurrent Sulfur and Phosphorus Incorporation in Nickel Cyclam-Based Complexes

We investigated the concurrent presence of S, P, and N donor atoms in isocyclam frameworks and their corresponding nickel complexes to get insight into the influence of these different heteroatoms on their structural and electronic properties. Structural elucidation of the complexes revealed both octahedral and square-planar coordination modes for Ni{PNSN} ({PNSN} = 8-phenyl-1-thia-5,11-diaza-8-phosphacyclotetradecane) and Ni{SNPN} ({SNPN} = 8-phenyl-1-thia-4,12-diaza-8-phosphacyclotetradecane). Moreover, it was found that in presence of different donor atoms, the one positioned between rigid ethyl moieties primarily controls the properties of the complexes. Thus, the transition between square-planar and octahedral conformers is slower for Ni{SNPN} as compared to Ni{PNSN}, which immediately adopts an octahedral geometry. A similar trend was observed when investigating the chemically generated NiI species via UV/vis/NIR and EPR spectroscopy: while Ni{SNPN} forms an intermediate NiI species that gradually converts to an undefined EPR-silent species, Ni{PNSN} exists as a stable NiI species.