LZnX complexes of tripodal ligands with intramolecular RN-H hydrogen bonding groups: structural implications of a hydrogen bonding cavity, and of X/R in the hydrogen bonding geometry/strength

J C M Rivas, R Prabaharan, R T M de Rosales, L Metteau, S Parsons

Research output: Contribution to journalArticlepeer-review

Abstract

Tripodal ligands N(CH2Py)(3-n)(CH2Py-6-NHR)(n) (R=H, n=1-3 L1-3, n=0 tpa; R=(CH2Bu)-Bu-t, n=1-3 L'(1-3)) are used to investigate the effect of different hydrogen bonding microenvironments on structural features of their LZnX complexes (X=Cl-, NO3-, OH-). The X-ray structures of [(L-2)Zn(Cl)](BPh4)2.0.5(H2O.CH3CN), [(L-3)Zn(Cl)](BPh4)3.CH3CN, [(L'(1))Zn(Cl)](BPh4) 1', [(L'(2))Zn(Cl)](BPh4)2'.CH3OH, and [(L'(3))Zn(Cl)](BPh4) 3' have been determined and exhibit trigonal bipyramidal geometries with intramolecular (internal) N-H...Cl-Zn hydrogen bonds. The structure of [(L'(2))Zn(ONO2)]NO3 4'.H2O with two internal N-H...O-Zn hydrogen bonds has also been determined. The axial Zn-Cl distance lengthens from 2.275 Angstrom in [(tpa) Zn( Cl)](BPh4) to 2.280-2.347 Angstrom in 1-3, 1'-3'. Notably, the average Zn-N-py distance is also progressively lengthened from 2.069 Angstrom in [(tpa)Zn(Cl)](BPh4) to 2.159 and 2.182 Angstrom in the triply hydrogen bonding cavity of 3 and 3', respectively. Lengthening of the Zn-Cl and Zn-N-py bonds is accompanied by a progressive shortening of the trans Zn-N bond from 2.271 Angstrom in [(tpa)Zn(Cl)](BPh4) to 2.115 Angstrom in 3 (2.113Angstrom in 3'). As a result of the triply hydrogen bonding microenvironment the Zn-Cl and Zn-N-py distances of 3 are at the upper end of the range observed for axial Zn-Cl bonds, whereas the axial Zn-N distance is one of shortest among N-4 ligands that induce a trigonal bipyramidal geometry. Despite the rigidity of these tripodal ligands, the geometry of the intramolecular RN-H...X-Zn hydrogen bonds (X=Cl-, OH-, NO3) is strongly dependent on the nature of X, however, on average, similar for R=H, (CH2Bu)-Bu-t.

Original languageEnglish
Pages (from-to)2800-2807
Number of pages8
JournalDalton Transactions
Issue number17
DOIs
Publication statusPublished - 2004

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