Coordination geometry of tetradentate Schiff's base nickel complexes: the effects of donors, backbone length and hydrogenation

The X-ray crystal structures of (N,N'-bis-(o-amidobenzilidene)-1,3-diaminopropane)nickel (Niambpr), (N,N'-bis-(o-amidobenzilidene)-1,4-diaminobutane)nickel (Niambut), (N,N'-bis-(o-thiobenzilidene)-1,4-diaminobutane)nickel(II) (Nitsalbut), {bis-acetonitrile-(N,N'-bis-(o-aminobenzyl)-1,2-diaminoethane)}nickel(II) tetrafluoroborate [Ni(H₄amben)(MeCN)₂] [BF₄]₂, {bis-O-acetato-(N,N'-bis-(o-aminobenzyl)-1,2-diaminoethane)}nickel(II) [Ni(H₄amben)(OAc)₂ · H₂O] and {bis-O-acetato-(N,N'-bis-(o-aminobenzyl)-1,3-diaminopropane)}nickel(II) [Ni(H₄ambpr)(OAc)₂] are presented. These structures complete the structural characterisation of the simple unsubstituted Schiff's base complexes with N₄ and N₂S₂ donor sets and allow us to assess the effects of donor groups and polymethylene chain length on the coordination geometries of nickel(II). The hydrogenated N4 complexes offer an insight into the effects of increased flexibility and character of the internal nitrogen donors. Unlike the parent N4 imine species the hydrogenated amine species do not deprotonate at the peripheral nitrogen donors and do not seem to be restricted to the meridial plane of the nickel.