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Issue 23, 1992
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The co-ordination chemistry of mixed pyridine–phenol and phenanthroline–phenol ligands; effects of π-stacking interactions and ligand rigidity on complex structures

Abstract

The crystal structures of [Cu2L22(µ-MeCO2)][PF6], [Ni2L22(µ-MeCO2)(MeCN)2][PF6] and [{NiL1(HL1)}2][PF6]2· 0.5MeCN·0.5Et2O [HL1 is the N,N,O-terdentate ligand 6-(2-hydroxyphenyl)-2,2′-bipyridine; HL2 is the new ligand 2-(2-hydroxyphenyl)-1,10-phenanthroline, an analogue of HL1 containing the more rigid 1,10-phenanthroline unit instead of 2,2′-bipyridyl] were determined. Both [Cu2L22(µ-MeCO2)][PF6] and [Ni2L22(µ-MeCO2)(MeCN)2][PF6] contain two ML2 units, in which the ligand is deprotonated and near-planar, stacked side by side such that the phenolates bridge resulting in M2(µ-O)2 cores in each case, with an additional bridging µ-1,3-acetate. The Ni2(µ-O)2 core is considerably contracted compared to the Cu2(µ-O)2 core, as the apical Cu–O(bridging phenolate) bonds are rather long (2.449 Å) due to Jahn–Teller distortion. The proximity of the two ML2 units results in π-stacking interactions between overlapping sections of the ligands. In contrast, [{NiL1(HL1)}2][PF6]2· 0.5MeCN·0.5Et2O consists of two pseudo-octahedral NiL12 units held together by two strong intermolecular hydrogen bonds between phenolate residues. As a result, sections of the ligands in each monomeric unit are brought into close contact resulting in additional inter-ligand stacking interactions which are optimised by considerable distortions of the ligands from planarity. There are thus two types of non-covalent intermolecular interaction in the dimer which appear to complement each other in a co-operative manner. The differences between the structures are discussed in relation to the different stereoelectronic preferences of the metal ions, and the different steric and electronic properties of the ligands.

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Article information


J. Chem. Soc., Dalton Trans., 1992, 3337-3344
Article type
Paper

The co-ordination chemistry of mixed pyridine–phenol and phenanthroline–phenol ligands; effects of π-stacking interactions and ligand rigidity on complex structures

B. M. Holligan, J. C. Jeffery and M. D. Ward, J. Chem. Soc., Dalton Trans., 1992, 3337
DOI: 10.1039/DT9920003337

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