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Decorating the Second Coordination Sphere in Pyrazolate‐Based Dinickel(II) Complexes with H‐Bond Donors
Author(s) -
Graef Tine,
Galezowska Joanna,
Dechert Sebastian,
Meyer Franc
Publication year - 2011
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201100514
Subject(s) - chemistry , bimetallic strip , protonation , crystallography , nickel , pyridine , ligand (biochemistry) , metal , deprotonation , chelation , hydrogen bond , coordination sphere , hydroxide , stereochemistry , acceptor , bond length , medicinal chemistry , crystal structure , ion , molecule , inorganic chemistry , organic chemistry , biochemistry , physics , receptor , condensed matter physics
Abstract Compartmental pyrazolate‐based ligands with bis(2‐pyridinylmethyl)aminomethyl or (2‐pyridinylmethyl)[2‐(1‐methylimidazolyl)methyl]aminomethyl chelate arms have been further elaborated by attaching pivaloylamido groups to the outer pyridine rings, giving the new ligands H 3 L 1 and H 3 L 2 . The peripheral pivaloylamido groups may serve as potential H‐bond donor or acceptor sites towards substrates in the bimetallic cavity. Protonation constants of the new ligand H 3 L 1 as well as its nickel(II) speciation in solution have been studied by pH potentiometry, revealing p K a = 8.9 for the metal‐bound water. Based on the X‐ray crystallographic structure of [Ni 2 (H 2 L 1 )(H 3 O 2 )(MeCN) 2 ](ClO 4 ) 2 ( 3 ) this p K a is rationalized in terms of two balancing effects, namely involvement of the pivaloylamido O atom in metal coordination and H‐bonding between the pivaloylamido NH group and the resulting nickel‐bound hydroxide. Complex 3 features a pyrazolate‐bridged dinickel(II) core and a bridging HO ··· H ··· OH unit within the bimetallic cavity, which is involved in multiple H‐bonding interactions.