Abstract
In this paper, the bromo- and phosphonate-ester-functionalized complexes [Zn(1)2][CF3SO3]2 and [Zn(2)2][CF3SO3]2 (1 = 4′-(4-bromophenyl)-2,2′:6′,2″-terpyridine, 2 = diethyl (4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)phosphonate) are reported. The complexes have been characterized by electrospray mass spectrometry, IR and absorption spectroscopies, and multinuclear NMR spectroscopy. The single-crystal structures of [Zn(1)2][CF3SO3]2.MeCN.1/2Et2O and [Zn(2)2][CF3SO3]2 have been determined and they confirm {Zn(tpy)2}2+ cores (tpy = 2,2′:6′,2″-terpyridine). Ongoing from X = Br to P(O)(OEt)2, the {Zn(4′-XC6H4tpy)2}2+ unit exhibits significant “bowing” of the backbone, which is associated with changes in packing interactions. The [Zn(1)2]2+ cations engage in head-to-tail 4′-Phtpy...4′-Phtpy embraces with efficient pyridine...phenylene π-stacking interactions. The [Zn(2)2]2+ cations pack with one of the two ligands involved in pyridine...pyridine π-stacking; steric hindrance between one C6H4PO(OEt)2 group and an adjacent pair of π-stacked pyridine rings results in distortion of backbone of the ligand. This report is the first crystallographic determination of a salt of a homoleptic [M{4′-(RO)2OPC6H4tpy}2]n+ cation.
Highlights
The oligopyridines are archetypal metal-binding domains used as scaffolds for numerous functional architectures [1,2,3]. 2,20 :60,200 -Terpyridines are of particular interest as they are readily accessible through simple synthetic procedures [4], and improvements to synthetic procedures continue to be reported [5]
Phosphonic acid anchoring groups have been shown to bind more strongly to semiconductor oxide surfaces than carboxylic acids and we have been interested in the use of the phosphonic acid anchoring ligands shown in Scheme 1
The phosphonic acid anchor has been shown to be effective in complexes containing {Ru(bpy)2 (CN)}+ [11,12], {Cu(bpy)2 }+ [13,14], and {Zn(tpy)2 }+ [15,16] cores (CN = a cyclometallating ligand such as the conjugate base of 2-phenylpyridine, bpy = 2,20 -bipyridine), and we have demonstrated that, in copper-based dyes, the presence of both a 1,4-phenylene spacer between a bpy metal-binding domain and the phosphonic acid is beneficial to Dye-sensitized solar cells (DSCs) performance [17]
Summary
The oligopyridines are archetypal metal-binding domains used as scaffolds for numerous functional architectures [1,2,3]. 2,20 :60 ,200 -Terpyridines (tpy) are of particular interest as they are readily accessible through simple synthetic procedures [4], and improvements to synthetic procedures continue to be reported [5]. The binding of the complex to the surface is through an anchoring ligand [10], which is typically an oligopyridine bearing carboxylic acid groups. The phosphonic acid anchor has been shown to be effective in complexes containing {Ru(bpy) (CN)}+ [11,12], {Cu(bpy)2 }+ [13,14], and {Zn(tpy)2 }+ [15,16] cores (CN = a cyclometallating ligand such as the conjugate base of 2-phenylpyridine, bpy = 2,20 -bipyridine), and we have demonstrated that, in copper-based dyes, the presence of both a 1,4-phenylene spacer between a bpy metal-binding domain and the phosphonic acid is beneficial to DSC performance [17]
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