Thioether-terminated nickel(ii) coordination clusters with {Ni6} horseshoe- and {Ni8} rollercoaster-shaped cores

Abstract

We report two polynuclear nickel(II) compounds whose supramolecular structures are controlled by small inorganic templating anions and π-conjugated Schiff-base ligands (L·SMe³⁻ and HL·SMe²⁻) with peripheral, structurally exposed methylthioether groups. The central component of the compound [Ni₆(L·SMe)₃(CO₃)(MeOH)₆(THF)₂]Cl·2MeOH (1, monoclinic space group P2/c) displays a horseshoe-shaped {Ni₆} core templated by μ₆-CO₃²⁻ moiety due to the fixation of atmospheric carbon dioxide. According to thermogravimetric analysis, compound 1 retains the structural integrity of its carbonate-bonded metal core [Ni₆(L·SMe)₃(CO₃)]⁺ up to ca. 390 °C. In the crystal lattice, compound 1 features an one-dimensional hydrogen-bonded chain structure [{CO₃ ⊂ Ni₆}⋯Cl⋯{CO₃ ⊂ Ni₆}]_∞. The structure of the compound [Ni₈(HL·SMe)₂(L·SMe)₂(OH)₄(MeCN)₄(H₂O)₄](NO₃)₂·11MeCN·2PhCN (2, triclinic space group P) consists of a dicationic crown-like {Ni₈} metallamacrocycle hosting two NO₃⁻ anions in the upper and lower cavities. The {Ni₆} complex is characterised by antiferromagnetic exchange interactions, whereas {Ni₈} reveals predominantly ferromagnetic exchange coupling between the spin-1 Ni(II) centres. The presence of terminal thioether anchoring groups at the periphery of complex 1, coupled with high thermal stability and solubility in several common organic solvents, renders this compound an interesting candidate for molecular surface-deposition from solution using electrospray ionisation mass spectrometry approach and, possibly, for supported-transition metal complex heterogeneous catalysis.