Di- and trinuclear complexes derived from hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P-O bond cleavage in the formation of [{(L'CuCl)₂(Co(NO₃)}Cl] (L' = N₃P₃(OC₅H₄N)₅(O))

Abstract

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl₃)], [L(CuCl)(ZnCl₃)], [L(CoCl)(ZnCl₃)], and [L(ZnCl₂)₂]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a η ⁵-gem-N₅ mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an η ¹-N₁ fashion. In the homobimetallic derivative, [L(ZnCl₂)₂], one of the zinc ions is five-coordinate (η ³-nongem-N₃), while the other zinc ion is tetracoordinate(η ²-gem-N₂). The reaction of L with CuCl₂ followed by Co(NO₃)₂·6H₂O yields a trinuclear heterobimetallic complex [{(L'CuCl)₂Co(NO₃)}Cl] [L' = N₃P₃(OC₅H₄N)₅(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)₂Co(NO₃)}Cl] [L' = N₃P₃(OC₅H₄N)₅(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens).