Crystal and molecular structure of chloro[NN′-di-(3-aminopropyl)-piperazine]nickel(II) chloride

Abstract

The structure of the title compound has been determined by a three-dimensional X-ray structural analysis, by use of 1967 independent reflections obtained photographically. Crystals are monoclinic with a= 7·85(3), b= 14·47(3), C= 14·14(3), β= 110·00(5)°, space group P2₁/c, and Z= 4. The structure was solved by conventional Patterson and Fourier techniques and refined by block-diagonal least-squares methods to R 0·084. The cation is five-co-ordinate with a geometry approximating to a square pyramid. The four nitrogens of the tetra-amine are closely co-planar, with the nickel 0·34 Å out of this plane towards the covalently bound chlorine [Ni–N(primary) 2·103(7) and 2·107(7); Ni–N(tertiary) 2·052(8) and 2·053(8); Ni–Cl 2·338(3)Å]. The N₄ plane, however, is distorted from a square by ligand constraints, so that N–Ni–N angles (between adjacent nitrogens) are 72·0(3)–95·2(3)°. Bond lengths within the cation have normal covalent values; the chloride ion forms a specific hydrogen-bonded ion-pair with the cation so as to be near the (sterically hindered)‘sixth co-ordination site’ of the nickel [Ni–Cl 3·395(3)Å]. The analysis shows the steric over-crowding of the ligand system (B-strain) which accounts for the low stability constants of its metal compounds.