A rod-like hexanuclear nickel cluster based on a bi(pyrazole-alcohol) ligand: structure, electrospray ionization mass spectrometry, magnetism and photocurrent response

Abstract

The reaction of one equivalent of 1,2-bis-(3,5-dimethylpyrazol-1-yl)-ethane-1,2-diol (H₂bdped) with two equivalents of Ni(OAc)₂·4H₂O afforded a hexanuclear nickel(II) cluster [Ni₆(bdped)₂(OAc)₈(H₂O)₄]·6EtOH (SD/Ni6a). The single-crystal X-ray diffraction (SCXRD) structural analysis reveals the one-dimensional zig-zag arrangement of six Ni(II) atoms that are in a slightly distorted octahedral coordination geometry. Two bdped²⁻ ligands show folded configurations to coordinate to Ni(II) atoms. Interestingly, the multi intra- and inter-cluster hydrogen bonds in and between the clusters could be favorable for the stability of the cluster and the cluster packing in the crystal. Electrospray ionization mass spectrometry (ESI-MS) reveals that the Ni₆ core structure keeps intact in solution and coexists with some fragments of Ni₄ and Ni₅ species. This fragmentation should be occurring in solution instead of the gas phase as indicated by in-source voltage dependent ESI-MS. Furthermore, SD/Ni6a displayed ferromagnetic exchange behavior arising from the interactions between the nickel(II) centers. UV-vis absorption presents typical Ni(II) species with octahedral coordination geometry and the photocurrent measurement gave fast and stable responses upon visible light illumination.