Synthesis, spectroscopic and structural properties of 2,2-dimethyl-propane-1,3-diamine copper(II) complexes. Temperature dependent tetragonal distortion in some thermochromic complexes. Crystal and molecular structure of bis(2,2-dimethylpropane-1,3-diamine)-diperchloratecopper(II)

Some compounds of the type [Cu(dmpd)2X2](dmpd = 2,2-dimethylpropane-1,3-diamine and X = Cl, Br, or ClO4) have been prepared and characterized by means of magnetic moments, e.s.r., electronic, and i.r. spectra. For one of them, bis(2,2-dimethylpropane-1,3-diamine) diperchloratocopper(II), the crystal structure has been determined by three-dimensional X-ray diffraction. Crystals are monoclinic, space group P21/c, with unit-cell dimensions: a= 9.724(2), b= 6.287(1), c= 16.191(3)Å, β= 97.66(1)°, and Z= 2. The structure has been refined to R= 0.036 8. Co-ordination around the copper is distorted tetragonal bipyramidal; two centrosymmetric chelate ligands form the base [Cu–N(1) 2.028(3), Cu–N(2) 2.021 (3)Å], and the two centrosymmetric unidentate perchlorate ions form the apices [Cu–O(1) 2.602(3)Å]. The electronic and i.r. spectra of the [Cu-(dmpd)2X2] complexes are temperature-dependent suggesting reversible continuous thermochromism arising through a temperature-dependent axial interaction between the anion and the CuN4 plane, with a more square form being favoured at higher temperature. Other complexes of the types [Cu(dmpd)X2] and [Cu(H2dmpd)X4](X = Cl or Br) were also prepared and investigated and their possible stereochemistries discussed.