Complexation of metal halides M′Cl_n by square-planar Schiff-base complexes, i.e. ML [M = Fe, Co, Ni, or Cu; L = acen =N,N′-ethylenebis(acetylacetoneiminate), salen =N,N′-ethylenebis(salicylideneiminate), or salphen =N,N′-o-phenylenebis(salicylideneiminate)] led to adducts which are intermediates in the exchange of the quadridentate ligand between M and M′. Exchange occurs if M′ is in an higher oxidation state than M. Concomitant redox and ionization reactions are observed. Reaction of [Fe(acen)], (1) with MCl₂·nthf (M = Fe or Zn) led to the bimetallic adducts [(thf)Fe(acen)MCl₂[M = Fe, (2); Zn, (3)] containing a square-pyramidal iron, while M has a tetrahedral co-ordination geometry. A complex analogous to (2), [ClFe(salphen)FeCl(thf)₂](4)(thf = tetrahydrofuran), was obtained by treating FeCl₂·1.5 thf with H₂ salphen in a 2:1 molar ratio in the presence of Na(OMe). This reaction gave some insight into the ligand-exchange pathway. The reaction of [M(acen)](M = Fe, Co, or Ni) complexes with TiCl₄·2thf in thf led to migration of the acen ligand to titanium and formation of [Ti(acen)Cl₂], (7) and the corresponding metal halide MCl₂·nthf. Related results have been obtained in the reaction of [M(acen)] and TiCl₃·3thf. When M = Ni or Cu complex (7) was obtained by exchange of the acen ligand and oxidation of titanium(III) by the corresponding metal halides. In the absence of a redox reaction, complexes of titanium (III) have been obtained: [Ti(acen)(thf)₂][CoCl₃(thf)], (10), and [Ti(acen)(thf)₂]₂[Fe₃Cl₈(thf)₂], (11), respectively. The structures of complexes (2)–(4), (10), and (11) have been determined by X-ray analysis: (2) space group P, a= 14.029(2), b= 9.854(1), c= 8.092(1)Å; α= 98.48(1), β= 90.96(1), γ= 107.44(1)°, Z= 2, and R= 0.065 for 1 360 observed reflections; (3), space group P, a= 14.006(3), b= 9.823(2), c= 8.077(2)Å, α= 98.49(1), β= 90.90(1), γ= 107.57(1)°Z= 2, and R= 0.072 for 2 347 observed reflections; (4), space group P2₁/c, a= 12.882(2), b= 11.940(2), c= 21.701 (3)Å, β= 95.40(1)°, Z= 4, R= 0.054 for 1991 observed reflections; (10), space group P, α= 12.735(3), b= 15.105(3), c= 8.935(2)Å, α= 95.30(2), β= 94.26(2), γ= 67.91 (2)°, Z= 2, and R= 0.055 for 2 576 observed reflections; (11), space group P, α= 14.109(3), b= 14.713(3), c= 9.203(2)Å, α= 99.98(2), β= 104.76(2), γ= 63.08(2)°Z= 1 for C₄₈H₈₄Cl₈Fe₃N₄O₁₀Ti₂ formula unit, and R= 0.050 for 2 685 observed reflections.