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Structural and spectroscopic insights on the coordination chemistry of the rigid heterotopic chelating ligand 1H-pyrazolo[4,3-h]quinoline

Goodwin, Jack W.; Kruger, Paul E.; Hawes, Chris S


Jack W. Goodwin

Paul E. Kruger


In this work we report the coordination chemistry of a rigid heterotopic ligand 1H-pyrazolo[4,3-h]quinoline HL1 in copper(II) and zinc(II) complexes for the first time, and examine both the structural properties and solution-phase behaviour of these species. On reaction with zinc(II) nitrate in acetonitrile, a mononuclear complex [Zn(HL1)2(OH2)2](NO3)2 1 is generated, where a size mismatch between the metal ion and the binding pocket leads to an anomalously long Zn-N bond to the pyrazole nitrogen atom. This is consistent with solution-state absorption and fluorescence measurements which indicate a relatively low stability constant logß of 9.1(3) in acetonitrile. The reaction of HL1 with copper(II) nitrate in methanol gave four new crystalline phases, the major forms of which being two polymorphs of the complex [Cu2(µ2-L1)2(NO3)2(MeOH)2] 2a and 2ß which also constitutes the dominant solution-phase behaviour of this mixture. Additionally, trace amounts of the nitric acid salt of HL1 were crystallised, along with the slow formation of a tetranuclear species [Cu4(µ2-L1)6(OH2)2](NO3)2·2MeOH 3 which also features anomalously long bridging distances from the L1 ligand as a result of its backbone rigidity.

Journal Article Type Article
Acceptance Date Nov 30, 2020
Publication Date Dec 28, 2020
Publicly Available Date May 26, 2023
Print ISSN 0095-8972
Publisher Taylor and Francis
Volume 74
Issue 1-3
Pages 341-360
Keywords Copper, ligand design, pyrazole, structural chemistry, zinc
Publisher URL