Substituent effects in the zinc(II) coordination chemistry of isomeric pyridylpyrazole ligands. Issue 8 (18th April 2019)

• Record Type: Journal Article
• Authors: Chen, Peng; Ge, Wei; Lu, Yangyang; Wu, Zhenghui; Xu, Jiachen; Woodfine, Sian E.; Darton, Richard J.; Hawes, Chris S.
• Is Part Of: Journal of coordination chemistry. Volume 72:Issue 8(2019)
• Page Start: 1395
• Page End: 1416
• Publication Date: 2019-04-18
• Subjects: Coordination chemistry -- pyrazole -- zinc -- crystallography -- fluorescence; Coordination compounds -- Periodicals; 541.2242
• DOI: 10.1080/00958972.2019.1587613
• Languages: English
• ISSNs: 0095-8972

Abstract

Abstract: Pyrazoles with unsymmetric substitution are useful ligands in coordination chemistry, but are under-developed due to synthetic challenges in accessing the pure isomers. We have prepared four new structurally related N -(2-pyridyl)-3, 5-dialkylpyrazole ligands, L1 –L4, and probed their coordination chemistry in the crystalline phase and in solution to elucidate a relationship between steric influence of the alkyl substituents, the stability of the subsequent metal complexes, and their crystal packing influences. We find thatL1 andL2, bearing linear or branched alkyl substituents, show similar stabilities and crystal packing motifs featuring π···π and C-H···Cl interactions in the crystalline complexes1 and2, respectively. The cyclohexyl-fused speciesL3 andL4 vary both in the solution stability of complexes3 and4, respectively, and in their crystal packing. Complex [ZnCl2 (L3 )] (3 ) is a mononuclear complex similar to1 and2, albeit with π···π interactions disallowed by the bulk of the cyclohexyl ring. Reaction of isomericL4 with ZnCl2 gives two polymorphic complexes, 4α and4β, of the form [Zn2 Cl2 (μ2 -Cl)2 (L4 )2 ], varying only in their long-range packing modes. These results show the importance of understanding the steric influences in substituted pyridylpyrazoles, which determine both stability in solution and speciation in the crystalline phase. Graphical Abstract: