Dissimilarities in trans-di(4-methoxybenzoato-O)-bis(1,3-diaminopropane-N,N′)M(II) (M = Cu, Ni) complexes

Article abstract of DOI:10.1016/S0020-1693(97)05532-1

The structures of trans-di(4-methoxybenzoato-O)bis(1,3-diaminopropane-N,N′)Cu(II) (1) and the corresponding nickel(II) analogue (2) were determined by single-crystal X-ray diffraction methods. The compounds crystallise in the monoclinic system, space group P2₁la (No. 14). 1:C₂₂H₃₂CuN₄O₆,M_r = 514.25,a = 10.318(2), b = 9.620(2), c = 12.7296(14) A, β = 103.910(14)°, V = 1226.5(4) A³,Z=2; 2: C₂₂H₃₂NiN₄O₆, M_r = 509.22, a = 10.100(2), b = 9.7220(11), c = 12.741 (5) A, β = 99.86(3)°, V = 1232.5(5) A³, Z=2. The compounds display crystal chemical isotypism. They are composed of discrete complex units connected by hydrogen bonds mediated by amino and carboxylate groups. Each complex unit consists of a central metal ion located at a centre of symmetry, six-membered chelate rings formed by 1,3-diaminopropane and axially coordinated para-methoxybenzoate anions. The most notable difference between the nickel (II) and copper(II) complex units is found in the axial M-O bond lengths, which are 2.144(2) and 2.497(4) A, respectively. The EHMO calculations assisted by ESR and magnetic susceptibility measurements give the values of 7 and 1% for the d-s mixing to explain the axial elongation in 1 and 2, respectively. Another difference is seen in the different skewness of the chelate rings. Although the hydrogen bonding network is similar in both compounds, there are clear differences in the N-H stretchings in the IR spectra. Differences in the relative thermal motions of the noncoordinated oxygen atoms of the carboxylate groups are probably dependent primarily on the central metal atom and secondarily on hydrogen bonding.