No abstract

A series of linear primary polyamines H2N–CH2–(CH–NH2)n–CH2–NH2 (1 ≤ n ≤ 3) was prepared from the corresponding polyalcohols. The polyamines were isolated as HCl adducts and the acidity constants in aqueous solution were determined. The crystal structure of the fully protonated tetraamine (n = 2) was elucidated by an X‐ray diffraction study. Complex formation of the triamine (n = 1) with Ni2+, Cu2+, Zn2+, Cd2+ was re‐investigated in aqueous solution. The pH‐dependent formation of a variety of species MxLyHz was established by potentiometric titrations and was compared with previous reports. The crystal structure of the Cu complex [CuL2]Cl2 exhibited a chain structure with a five‐coordinate CuII centre in which two amino groups of the triamine ligands are coordinated to one Cu centre, while the third amino group of one of the ligands is bonded to a neighbouring Cu atom. The compound shows weak antiferromagnetic coupling interactions between the CuII centres within the chain.

Keywords: Amine ligands / Chelates / Ligand design / Stability constantsThe protonation and metal complex formation of the branched pentaamine ligand 2,2,6,6-tetrakis(aminomethyl)-

The structures of 3-amino-1,2R,4S,5-tetraammoniopentane tetrachloride monohydrate, C 5 H 21 N 5 4+ Á4Cl À ÁH 2 O, and 1,2R,3,4S,5-pentaammoniopentane tetrachlorozincate trichloride monohydrate, (C 5 H 22 N 5 )[ZnCl 4 ]Cl 3 ÁH 2 O, have been determined from single-crystal X-ray diffraction data. Both compounds show a complex network of NÐHÁ Á ÁO, OÐ HÁ Á ÁCl and NÐHÁ Á ÁCl hydrogen bonds. There are a total of 14 H atoms of the tetra-cation and 15 H atoms of the pentacation available for hydrogen bonding. However, due to the particular shape of the primary linear polyammonium cations, only a certain number of H atoms can be involved in hydrogen-bond formation. It is further shown that hydrogen bonding has an in¯uence on the conformation of such alkylammonium cations.

The cover picture shows a perspective view of an octanuclear Ni II complex with the quadridentate ligand threo-1,2,3,4-tetraaminobutane (red: Ni II , blue: N, H omitted). The eight Ni II centers, which form the vertices of a slightly disordered cube, have alternate L and D configurations. The twelve chiral ligand molecules are located at the edges of this cube and generate an [Ni 8 L 12 ] 16 cage of idealized T symmetry. The cuboidal structure has a rather large and highly chiral cavity of about 12 in diameter. The bis-bidentate coordination mode of the tetraamine ligand has also been observed in a series of polynuclear Cu II solid-state structures, exhibiting infinite two-and threedimensional porous networks, helices, and ring structures. This ligand has considerable potential as a building block for chiral coordination polymers. The solid-state structures together with a comprehensive solution study of these complexes are described in detail by K. Hegetschweiler et al. on p. 917 ff.