SHORT AND NEARLY SYMMETRICAL INTRA-MOLECULAR HYDROGEN-BOND - X-RAY AND NEUTRON-DIFFRACTION ANALYSIS OF 2,2'-(1,3-DIAMINOPROPANE)BIS(2-METHYL-3-BUTANONE OXIMATO)NICKEL(II) CHLORIDE HYDRATE

A combined room-temperature neutron and X-ray diffraction study of hydrated 2, 2ʹ-(l, 3-diaminopropane)bis(2-methyl-3-butanone oximato)nickel(II) chloride, [Ni(PnAO-H)]-xH20, [Ni(C13H27N4O2)]Cl-xH20 (x = 1 or 1.5), has been performed to investigate the influence of steric requirements of the ligand and the size of the metal ion on the short intramolecular O…O hydrogen bond. [Ni(PnA0-H)]Cl•xH20 crystallizes with four molecules in an orthorhombic unit cell of symmetry P212121with a = 10.997 (4) Å, b = 12.683 (5) Å and c = 13.369 (4) A for the monohydrated complex. Three-dimensional Patterson and Fourier methods followed by full-matrix least-squares refinement gave R(Fi) = 0.081 with 1637 neutron data and R(F2) = 0.064 with 2501 X-ray data. The complex cation has square-planar coordination about the nickel atom. The water molecule and chloride ion are extensively hydrogen bonded to each other and to the amine hydrogen atoms of the cation. The hydrogen atom in the intramolecular hydrogen bond is nearly symmetrically disposed in the O—H…O bond with a short (2.409 (10) A)… 0 distance. The O-H bond lengths for the hydrogen bond are 1.16 (2) and 1.26 (2.) A and the O-H-O angle is 170 (1)°. The potential for the intramolecular hydrogen bond apparently has a broad and nearly symmetrical single minimum. The methyl groups attached to sp2carbon atoms have large rotational amplitudes resulting in short apparent C-H bond lengths (1.04 (3) A average). Other average uncorrected bond distances involving hydrogen atoms are O-H (in H20) = 0.92 (4) Å N-H = 1.04 (1) Å and C-H = 1.08 (3) A for methyl groups attached to sp3carbon atoms. A comparison with the reported work on the a-amine oxime (AO) complexes has shown that the earlier conclusion about the resemblance of steric requirements of PnAO and two coordinated AO's is maintained. The Ni-N(amine) and Ni-N(oxime) distances in the present complex are 0.04-0.05 A longer than the corresponding distances in Ni(II)-AO and-EnAO complexes, whereas the O…O distance is about 0.06 A shorter than that observed in the EnAO-Ni(II) complex. The predicted thermodynamic stability based upon bond distances is in good agreement with the observed thermodynamic and spectral data on nickel(II)-a-amine oxime complexes. © 1979, American Chemical Society. All rights reserved.