The exploration of supramolecular interactions stemming from the [UO₂(NCS)₄(H₂O)]²⁻tecton and substituted pyridinium cations

Abstract

The synthesis and crystal structures of eight compounds containing the anionic uranyl isothiocyanate tecton [UO 2 (NCS) 4 (H 2 O)] 2− , charge balanced by substituted pyridinium cations (4XpyH: X = Cl, Br, I, SCN, CH 3 , NH 2 , N(CH 3 ) 2 ) are reported. Hydrogen bonding interactions between coordinated water molecules and the non-coordinated sulfur atoms (O-H 2 ⋯S) of the adjoining tectons facilitate the formation of infinite 'pseudo' chains of inorganic tectons. The substituted pyridinium cations were paired with these fixed uranyl isothiocyanate tectons due to their ability to sustain multiple intermolecular interactions with the sulfur atoms of the uranyl tectons, thus promoting assembly. The variation of the substituent group bound to the organic cations allowed for the resulting non-covalent interactions to be systematically assessed in order to determine their relative effects upon packing. Additionally, respective acceptor-donor pairings as well as the relative strengths of the halogen, pseudohalogen [C-X⋯A (X = Cl, Br, I, SCN and A = O, S)] and hydrogen bonding [R-H⋯A (R = N, C and A = O, S, π)] interactions were investigated. The acceptor-donor relationships emulated hard-soft pairings and consequently increased in strength as a function of this trend.

Crystallization in Ionic Liquids: Synthesis, Properties, and Polymorphs of Uranyl Salts

“…As expected, the uranyl cation is coordinated by thiocyanates using nitrogen linkages, as observed in the series of counter cations, e.g., imidazolium, 24 ammonium, 27,81 and others. 82 The UO bond distance of 1.766 (8) In comparison with our structure investigations, the more interesting features of compound 2 may have arisen from the phase transformations that remained undefined in previous solutions studies, which will be illustrated later in this work.…”

Restricted Speciation and Supramolecular Assembly in the 5f Block

“…Figure adapted from ref. (R. G. Surbella III, C. L. Cahill, CrystEngComm 2014 , 16 , 2352). Reproduced by permission of The Royal Society of Chemistry.…”

“…The SCN − ligands are exclusively N‐bound to the uranyl cation and consequently allow for the terminal S atoms to act as HB or XB acceptors. Moreover, coordinated water molecules in the (C 5 H 5 NX) 2 [UO 2 (NCS) 4 H 2 O] (X=Cl, Br, I, SCN, CH 3 , NH 2 , N(CH 3 ) 2 ) system are at the core of a robust assembly motif that promotes chains of [UO 2 (NCS) 4 H 2 O] 2− anions via Ow−H⋅⋅⋅S HBs, which then assemble into higher dimensions via XBs or HBs donated by the cations (Figure ) . These materials highlight NCI pairings that follow hard/soft acid‐base trends and we note some (atypical) uranyl oxo engagement with less polarizable Cl donors, whereas the terminal S atoms of the SCN − ligands were acceptors for the larger Br and I donors.…”

“…Beyond structural interests, however, we note deep‐red crystal colors, pronounced thermochromism, and additional vibronic features in their luminescence spectra (Figure ) . These properties are not commonly observed among uranyl containing materials, and are a unique characteristic of the uranyl‐isothiocyanate system . Each phenomena required a separate computational analysis as a clear crystallographic explanation for the thermochromism and luminescence was insufficient to explain the origin of these observations.…”

A Structural and Spectroscopic Study of the First Uranyl Selenocyanate, [Et4N]3[UO2(NCSe)5]

“…Also present in the structure are close contacts between a coordinated selenium atom and the selenium of the non-coordinated [NCSe]´(3.427(1) Å) that are shorter than the van der Waals radii (3.64 Å) [19]. Chalcogen-chalcogen interactions have been studied both experimentally [21,22], and in the case of [NCS]´also for uranyl (S¨¨¨S = 3.536(2) Å) [15], and theoretically [23,24]. This may explain the difficulty in growing single crystals of 1 as these weak interactions may be important.…”