Anion-directed template synthesis and hydrolysis of mono-condensed Schiff base of 1,3-pentanediamine and o-hydroxyacetophenone in Ni^II and Cu^II complexes

Abstract

Bis(o-hydroxyacetophenone)nickel (II) dihydrate, on reaction with 1,3-pentanediamine, yields a bis-chelate complex [NiL₂]•2H₂O (1) of mono-condensed tridentate Schiff baseligand HL {2-[1-(3-aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the Ni^II as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)₂•4H₂O furnishing the complex [NiL(NCS)] (2) and with CuCl₂•2H₂O in the presence of NaN₃ or NH₄SCN producing [CuL(N₃)]₂ (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO₄)₂•6H₂O and Cu(NO₃)₂•3H₂O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H₂O)]ClO₄ (5) and [Cu(hap)(pn)(H₂O)]NO₃ (6), respectively (Hhap = o-hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO₄)₂•6H₂O or Ni(NO₃)₂•6H₂O to yield [Ni(hap)₂] (7). The structures of the complexes 2, 3, 5, 6 and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, Ni^II possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group. The coordination environment around Cu^II in complex 3 is very similar to that in complex 2 but here two units are joined together by end-on, axial-equatorial azide bridges to result in a dimer in which the geometry around Cu^II is square pyramidal. In both 5 and 6, the Cu^II atoms display the square-pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3-pentanediamine and two oxygen atoms of o-hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square-planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one-dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2-D net-like open frameworks.