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Issue 48, 2016
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Dynamic neighbouring participation of nitrogen lone pairs on the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(II) coordination platforms

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Abstract

The participation of neighbouring nitrogen lone pairs in the chromogenic control of trans-bis(salicylaldiminato)Pt(II) platforms was examined, using newly designed Pt analogues bearing salicylaldehyde hydrazone ligands. A series of non-vaulted and vaulted Pt complexes (1–5) with salicylaldehyde hydrazones as trans-coordinated bidentate ligands were synthesized and characterized with regard to the chromogenic behaviour of the trans-bis(salicylaldiminato)Pt(II) coordination platforms. X-ray diffraction and 2D NMR data demonstrated that, in the case of the non-vaulted N-monomethyl complexes 1, there was significant participation of neighbouring N(2) lone pairs in the d–π conjugation of the trans-bis(salicylaldiminato)Pt(II) platforms owing to conformational fixation arising from intramolecular hydrogen bonding. In contrast, the lone pairs of the N,N-dimethyl analogues 2 made a much less significant contribution to the extension of the d–π conjugation, due to their high conformational mobility. Complexes 1–5 were found to have structure-dependent chromogenic properties in the solution state, such that the absorption spectra of the N-methyl, short-vaulted complexes 1 and 3 exhibited significant hypsochromic shifts relative to the N,N-dimethyl, long-vaulted analogues 2 and 5, which had spectra very similar to that of the trans-bis(salicylaldiminato)Pt(II) complex 6. The introduction of MeO groups at the 3- and 5 positions on the aromatic rings of 1 and 2 gave rise to significant hypsochromic and bathochromic shifts, respectively. In addition, νmaxET(30) plots for various solvents revealed that complexes 1–5 exhibit negative solvatochromism, in which the data obtained in alcoholic solvents are hypsochromically separated from those in non-alcoholic solvents for 1 and 3, an effect that is not observed for 2 and 5. Complexes 1–5 also exhibit emission enhancement upon addition of excess CH3SO3H in dimethyl sulfoxide, and a significant effect of the linker on quantum yields (Φ77 K) was observed in the case of the vaulted complexes. Density functional theory calculations (B3LYP/6-31G*, LanL2DZ) determined that the structure dependence of the chromogenic behaviour of these non-vaulted and polymethylene-vaulted hydrazone complexes can be attributed to variations in the participation of neighbouring nitrogen lone pairs in the d–π conjugation on the trans-bis(salicylaldiminato)Pt(II) coordination platforms.

Graphical abstract: Dynamic neighbouring participation of nitrogen lone pairs on the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(ii) coordination platforms

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Publication details

The article was received on 19 Oct 2016, accepted on 14 Nov 2016 and first published on 14 Nov 2016


Article type: Paper
DOI: 10.1039/C6DT04005E
Citation: Dalton Trans., 2016,45, 19257-19268
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    Dynamic neighbouring participation of nitrogen lone pairs on the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(II) coordination platforms

    T. Hashimoto, K. Fukumoto, N. H. Le, T. Matsuoka, S. Kawamorita, N. Komiya and T. Naota, Dalton Trans., 2016, 45, 19257
    DOI: 10.1039/C6DT04005E

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