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

Abstract

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.

Citation

Goodwin, J. W., Kruger, P. E., & Hawes, C. S. (2020). Structural and spectroscopic insights on the coordination chemistry of the rigid heterotopic chelating ligand 1H-pyrazolo[4,3-h]quinoline. Journal of Coordination Chemistry, 74(1-3), 341-360. https://doi.org/10.1080/00958972.2020.1868041

• Journal Article Type: Article
• Acceptance Date: Nov 30, 2020
• Publication Date: Dec 28, 2020
• Publicly Available Date: May 26, 2023
• Journal: JOURNAL OF COORDINATION CHEMISTRY
• Print ISSN: 0095-8972
• Publisher: Taylor and Francis
• Volume: 74
• Issue: 1-3
• Pages: 341-360
• DOI: https://doi.org/10.1080/00958972.2020.1868041
• Keywords: Copper, ligand design, pyrazole, structural chemistry, zinc
• Publisher URL: https://www.tandfonline.com/doi/full/10.1080/00958972.2020.1868041