Second-sphere coordination of 5,5 '-diamino-2,2 '-bipyridine metal complexes with oxygen ligands through N-H center dot center dot center dot O hydrogen bonding

摘要

Tris(5,5'-diamino-2,2'-bipyridine)metal complexes, [M(DABP)(3)](2+) with M = nickel(II), zinc(II) or iron(II) can be engaged in hydrogen-bonding interactions from the amino groups to oxygen-containing molecules as H-bond acceptors. This so-called second-sphere coordination of the metal complexes is investigated here by using 18-crown-6 (18-C-6) and the 1,3,5-benzene-tricarboxylate (BTC) anion for N-(HO)-O-... bonding. Single-crystal X-ray structural studies show that [Ni(DABP)(3)](2+) or [Zn(DABP)(3)](2+) and 18-C-6 form strands of alternating [M(DABP)3]2+ and 18-C-6 units with only two out of six amino groups getting involved in weak (NHO)-O-... bonding. The remaining NH2 groups are hydrogen bonded to the chloride and nitrate anion, respectively, and solvent molecules of crystallization. The anionic BTC hydrogen-bond acceptor, however, is capable of capping the triangular face formed by the three amino groups in [M(DABP)(3)](2+). In {[Fe(DABP)(3)] (BTC)(2)}(4-) the capping occurs by two BTC units from both sides, i.e. for both triangular faces and engages all six NH2 groups of the metal complex. Charge compensation is provided by two hydrated {[Fe(DABP)(3)](.)aq}(2+) complexes per formula unit. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 53]