Where Are the tpy Embraces in [Zn{4′-(EtO)2OPC6H4tpy}2][CF3SO3]2?

Abstract

In this paper, the bromo-and phosphonate-ester-functionalized complexes [Zn(1) 2 ] [CF 3 SO 3 ] 2 and [Zn(2) 2 ][CF 3 SO 3 ] 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 ][CF 3 SO 3 ] 2 . MeCN .1 / 2 Et 2 O and [Zn(2) 2 ][CF 3 SO 3 ] 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 -XC 6 H 4 tpy) 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 C 6 H 4 PO(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) 2 OPC 6 H 4 tpy} 2 ] n+ cation. Crystals 2018, 8, x FOR PEER REVIEW 2 of 11 presence of the 1,4-phenylene spacer enhances the rate of electron-transfer across the dye/semiconductor interface [23]. Scheme 1. Examples of anchoring ligands (cyclometallating H(C^N), bpy N^N, and tpy N^N^N) used in sensitizers in metal complex dyes in dye-sensitized solar cells.Despite the interest in sensitizers based on polypyridine metal complexes incorporating phosphonic acid anchors, there is remarkably little crystallographic data available to provide insights into structural details, in particular, packing interactions that may influence aggregation of the surface-adsorbed species. A search of the CSD (v. 5.40, November 2018 [24] for metal-bonded {4′-O3P-tpy} or {4′-O3P-C6H4tpy} units gave surprisingly few hits [25][26][27][28][29][30][31][32], with only one featuring a 1,4-phenylene spacer [32]. It is also interesting to note that all of the reported structures relate to phosphonate esters rather than the parent phosphonic acids, and that the majority of the studies were motivated by application of the complexes as logic gates, photosensitizers, and catalysts. Here, we report the syntheses and single-crystal structures of the two zinc(II) complexes [Zn(1)2][CF3SO3]2 and [Zn(2)2][CF3SO3]2 (where ligands 1 and 2 are defined in Scheme 2) and investigate the effects that the phosphonate ester group has on intermolecular interactions in the solid state.Scheme 2. Structures of the ligands 1 and 2. Materials and Methods General1 H, 13 C, and 31 P NMR spectra were recorded on a Bruker Avance III-500 spectrometer (Bruker BioSpin AG, Fällanden, Switzerland) at 298 K. The 1 H and 13 C NMR chemical shifts were referenced with respect to residual solvent peaks (δ TMS = 0), and 31 P shift with respec...

Metal Phosphonates and Phosphinates

“…The second article is entitled "Where Are the tpy Embraces in [Zn{4 -(EtO) 2 OPC 6 H 4 tpy} 2 ][CF 3 SO 3 ] 2 ?" [11] and reports on the synthesis and structural characterization of homoleptic Zn complexes containing terpyridine ligands functionalised with either phosphonate or bromo groups. Structural analysis reveals that the presence of bulky diethylphosphonate pending groups introduces steric hindrance and affects the packing interactions, resulting in significant distortion of the ligand backbone, which is not observed in the bromo derivative.…”