Cis- and trans-Dichloro-derivatives of six- and seven-co-ordinate zirconium and hafnium bonded to quadridentate Schiff-base ligands. Crystal structures of [Zr(acen)Cl2(thf)], [M(salphen)Cl2(thf)]·0.5thf, [M(acen)Cl2], (M = Zr or Hf), and [Zr(msal)Cl2][acen =N,N′-ethylenebis(acetylacetoneiminate), salphen =N,N′-o-phenylenebis(salicylideneiminate), msal =N-methylsalicylideneiminate, and thf = tetrahydrofuran

Abstract

The reaction of MCl4·2thf (thf = tetrahydrofuran) with the sodium salt of quadridentate Schiff bases [L =N,N′-ethylenebis(acetylacetoneiminate)(acen), N,N′-ethylenebis(salicylideneiminate)(salen), N,N′-ethylenebis(α-methylsalicylideneiminate)(dmsalen), or N,N′-o-phenylenebis(salicylideneiminate)(salphen)] yields the complexes [MLCl2(thf)]. X-Ray analyses showed for all of them that the metal ion is seven-co-ordinate with a pseudo-pentagonal bipyramidal geometry. Details of the structures of [Zr(acen)Cl2(thf)](5), [Zr(salphen)Cl2(thf)]·0.5thf (10), and of the corresponding isostructural hafnium complex [Hf(salphen) Cl2(thf)]·0.5thf (11) are reported. The equatorial plane of the bipyramid is defined by the N2O2 donor atoms and by the oxygen atom from thf, while the two chlorine atoms are trans to each other [Cl–Zr–Cl 169.1 (1), (5); 165.2(1), (10); Cl–Hf–Cl 166.3(1)°, (11)]. Recrystallization of the seven-co-ordinate complexes from toluene removed the thf leading to six-co-ordinate complexes. The structural determination of the isostructural [Zr(acen)Cl2](12) and [Hf(acen)Cl2](13) showed the six-co-ordination of the metal with the two chlorines assuming a cis arrangement [Cl–Zr–Cl 87.2(1), (12); Cl–Hf–Cl 87.4(1)°, (13)]. Bond lengths within the co-ordination sphere are significantly shorter in the six-co-ordinate complexes. The cis and trans isomers do not interconvert in solutions of non-co-ordinating solvents, i.e. C6H6 or CH2Cl2, as shown by their distinctive 1H n.m.r. spectra. In the absence of geometrical constraints zirconium(IV) prefers six-co-ordination and a cis arrangement of the chloride ligands. This was confirmed by synthesizing [Zr(msal)2Cl2](15)(msal =N-methylsalicylideneiminate), [Cl–Zr–Cl 97.9(1)°] containing a bidentate Schiff-base ligand. Its crystallization from thf gave the unsolvated six-co-ordinated form. Crystallographic details: complex (5), space group P, a= 8.401 (1), b= 15.987 (2), c= 7.805(1)A, α= 98.41 (1), β= 90.32(1), γ= 76.65(1)°, Z= 2, and R 0.042 for 3 713 observed reflections; (10), space group P, a= 12.759(2), b= 13.332(2), c= 7.587(1)A, α= 91.60(2), β= 98.45(1), γ= 85.30(1)°, Z= 2, and R 0.033 for 3 813 observed reflections; (11), space group P, a= 12.737(7), b= 13.269(7), c= 7.564(4)A, α= 91.48(1), β= 98.56(1), γ= 85.26(1)°Z= 2, and R 0.027 for 4 227 observed reflections; (12), space group P21/n, a= 24.150(5), b= 9.160(2), c= 7.282(1)A, β= 90.90(1)°, Z= 4, and R 0.034 for 1 894 observed reflections; (13), space group P21/n, a= 24.096(10), b= 9.161 (4), c= 7.262(3)A, β= 90.87(1)°, Z= 4, and R 0.024 for 2 124 observed reflections; (15), space group P, a= 13.024(3), b= 14.522(3), c= 9.797(2)A, α= 90.10(1), β= 93.14(1), γ= 96.09(1)°, Z= 4, and R 0.044 for 3 294 observed reflections.