Group 12 metal complexes of tetradentate N 2O 2–Schiff-base ligands incorporating pyrazole : Synthesis, characterisation and reactivity toward S-donors, N-donors, copper and tin acceptors

Abstract

New [M(Q) 2(X)] derivatives (where M=Zn, Cd or Hg; Q=1-phenyl-3-methyl-4-R(C=O)-pyrazolon-5-ato; in detail: Q L, R=C 6H 5; Q B, R=CH 2C(CH 3) 3; Q S, R=CH(C 6H 5) 2; X=EtOH or H 2O) have been synthesised and characterised. These compounds undergo a condensation reaction with the appropriate diamine in ethanol, affording novel Schiff-base metal derivatives [M(diaquo)bis(1-phenyl-3methyl-4-R(C=N)-pyrazolone)(CH 2) n diimmine] (L nH 2, R=C 6H 5, n=2, 3 or 4; B nH 2, R=CH 2C(CH 3) 3, n=2, 3 or 4; S nH 2, R=CH(C 6H 5) 2, n=2 or 3; M=Zn, Cd or Hg). These compounds possess a six-coordinate metal environment. A 113Cd NMR study has been carried out on cadmium derivatives. The derivative [Zn(L 2)(H 2O) 2] reacted with CuCl 2 and with Cu(ClO 4) 2 affording [Cu(Q L) 2] and [Cu(en) 2](ClO 4) 2 (en=ethylendiamine), respectively, upon breaking of the C=N bond in the Schiff-base donor. In addition [Zn(L 2)(H 2O) 2] reacted with 1,10-phenanthroline (phen), yielding the derivative [Zn(Q L) 2(phen)]. Whereas when [Zn(L 2)(H 2O) 2] reacted with CdCl 2, formation of [Cd(L 2)(H 2O) 2] due to exchange of the metal centre was observed. Finally the derivative [Zn(L 2)(Hmimt)], likely containing a five-coordinate ZnN 2O 2S central core, has been obtained from the exchange reaction between [Zn(L 2)(H 2O) 2] and 1-methylimidazolin-2-thione (Hmimt).