The Crystal Structure of Ethylenebis(biguanidine)nickel(II) Dichloride Monohydrate

The crystal structure of ethylenebis(biguanidine)nickel(II) dichloride monohydrate, Ni(C_6H_(16)N_(10))Cl_2.H_2O, has been determined and refined on the basis of three-dimensional intensity data collected on an automated diffractometer. The crystals are monoclinic, space group P2_1/c, with cell dimensions ɑ = 6-911, b = 11·678, c = 18·055 Å, β = 101·39°; there are four molecules in the cell. The structure was determined by Patterson methods and refined by least-squares to an R index of 0·048 and a goodness-of-fit of 1·11 for 2879 reflections of non-zero weight. The resulting standard deviations in the atomic positions are about 0·002-0·003 A for the C, N and 0 atoms, 0·02-0·03 Å for the H atoms and less than 0·001 Å for Ni and CI-. The organic ligand is tetradentate and forms a square-planar array about the central nickel atom; the average Ni-N distance is 1 ·865 Å. Chemically equivalent bonds are equal in length within experimental error, and the bond distances have been satisfactorily correlated with molecular-orbital and valencebond descriptions of the cation. All available hydrogen atoms are involved in hydrogen bonds to chloride ions or water molecules. An interesting feature is that, in spite of considerable double-bond character in the C-N bonds, many of the hydrogen atoms are displaced appreciably from the plane of the cation toward the hydrogen-bond acceptors; the bonding about the nitrogen atoms thus becomes pyramidal