The Structural Systematics of Protonation of Some Important Nitrogen‐base Ligands. I Some Univalent Anion Salts of Doubly Protonated 2, 2′:6′, 2″‐Terpyridyl

Abstract

A number of salts of 2,2Ј:6Ј,2Љ -terpyridyl ('tpy') with univalent anions (halides : X ϭ Cl, Br, I; oxyanions of increasing basicity: ClO 4 , NO 3 , 'tfa' ϭ trifluoroacetate, 'tca' ϭ trichloroacetate), variously solvated, have been structurally characterized by single crystal X-ray studies. In all cases the tpy moieties are found to be doubly protonated [tpyH 2 ] 2ϩ , the hydrogen atoms being associated with the nitrogen atoms of the peripheral rings, these together with the central nitrogen atom being directed towards a common focus, in most cases 'chelating' one of the counter-ion components in diverse ways. Thus the chloride and bromide compounds are isomorphous [(tpyH 2 )X] ϩ X Ϫ ·H 2 O arrays; a second dihydrate phase is also described for the chloride, the two forms having the unchelated anion and water molecules engaged in hydrogen-bonded networks essentially independent of [(tpyH 2 )X] ϩ . The iodide is anhydrous, and of a different structural type, the anions, presumably 1293 too large for chelation, lying out of plane to either side, and linking different cations into a one-dimensional polymer; in the perchlorate, the unsolvated aggregate is now discrete [(tpyH 2 )X 2 ], a pair of perchlorate ions disposed to either side of the tpy plane, lying each with one oxygen atom interacting with both of the two protonating hydrogen atoms. In the anhydrous X ϭ NO 3 , tfa, tca arrays, the lattices are solvated by the parent acids; one oxygen atom of each anion is chelated by the [tpyH 2 ] 2ϩ as in the chlorides, the other anion, with the acid, forming an independent 'acid salt' counterion [XHX] Ϫ in each case, retaining the additional protonic hydrogen rather than further protonating the central ring, all being of the form [(tpyH 2 )X]X·HX ϭ [(tpyH 2 )X][X(HX)].

Remarkable emissions in diprotonated 2,2′:6′,2″‐terpyridine derivatives

“…The diprotonated terpyridine cation (terpyH) has been prepared3–7 and the effect of anions on the structures of terpyridine derivatives has also been reported from both theoretical and experimental bases 8–12. 4′‐Chloro‐2,2′:6′,2′′‐terpyridine hydrochlorate hexafluorophosphate [ClterpyH 2 ClPF 6 ( 3 )] and 4′‐chloro‐2,2′:6′,2′′‐terpyridine hydrochlorate tetrafluoroborate (ClterpyH 2 Cl·BF 4 ) in the solid state exhibited different crystallographic symmetries, molecular structures, and packing patterns 12.…”

Anion Influence of Emission Properties and DFT Calculations of Diprotonated and Triprotonated Terpyridines

“…One doublet at 8.99 ppm in 2Cl was observed. In 2Cl , downfield shifts relative to those of tterpy were also observed in all the H protons . These upfield shifts were induced by the mesomeric effect of the attachment of tolyl substituent.…”

“…Terpyridine (terpy) is generally known to form trans ‐ trans conformation . The attachment of one proton to terpy makes its structure cis ‐ trans conformation . The crystal structure of 2,2′:6′,2′′‐Terpyridinium dinitrate has been reported by Berthon et al.…”

The Structural Systematics of Protonation of Some Important Nitrogen‐base Ligands. II. Some Univalent Anion Salts of Singly Protonated Bis(2‐pyridyl)amine

“…Salts of dipyridylamine were obtained as colourless crystalline solids on the millimolar scale, from an aqueous solution of the appropriate acid in excess in each case, all containing the monoprotonated cation. Following the record, structurally substantiated, of doubly protonated cations [dpaH 2 ] 2ϩ as the tfs and (CuCl 4 ) 2Ϫ salts in the literature [5,8], our attempts to obtain and confirm this species by recrystallization from/with a variety of other strong acids www.zaac.wiley-vch.de were, interestingly, unsuccessful, although, as with tpy [1], 'acid salts' were obtained with some species, again including the strong acid HNO 3 , defining the extra proton location to be in association with anionic moieties rather than the dpa species. Dipyridylamine (dpa) was treated with the following aqueous acids: trichloroacetic acid (Htca), HClO 4 , HI, HBr, HNO 3 , and HClO 4 , pure bulk samples being obtained for the following.…”

“…Bis(2-pyridyl)amine, 'dipyridylamine' ϵ 'dpa', (C 5 H 4 N) 2 -NH, constructed, like 2,2Ј:6Ј,2Љ-terpyridyl, 'tpy', by the symmetrical substitution of a pair of pyridine rings for two hydrogen atoms of a central amine [1], could, hypothetically, behave in a similar manner as a tridentate ligand, a concept in practice not realized in the numerous examples available because of considerably different geometrical and electronic considerations, so that dpa behaves primarily as a chelate, with the central nitrogen atom directed away from the metal atom, or, less frequently, as a unidentate. Despite the single bonds to the central nitrogen atom, it normally presents as a planar array, a feature which impacts on the basicity of that nitrogen atom, which also is essentially planar.…”