Neutral thioether and selenoether macrocyclic coordination to Group 1 cations (Li – Cs) – synthesis, spectroscopic and structural properties

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X-ray crystallography
Crystals were obtained as described below. Details of the crystallographic data collection and refinement are in Table 1. Diffractometer: Rigaku AFC12 goniometer equipped with an enhanced sensitivity (HG) Saturn724+ detector mounted at the window of an FR-E+ SuperBright molybdenum rotating anode generator (λ 1 = 0.71073 Å) with VHF Varimax optics (70 or 110 µm focus). Cell determination and data collection: Crystal-Clear-SM Expert 3.1 b27, data reduction, cell refinement, and absorption correction: CrystalClear-SM Expert 2.1 b29. 13 Structure solution and refinement were carried out using Olex2 or WinGX and software packages within. 14 Disorder in the CF 3 groups of the [BAr F ] − anions was present in all of the structures, which is often observed in compounds containing [BAr F ] − , 15 and this was satisfactorily modelled using DFIX, DANG, DELU and SIMU restraints. Positional disorder was also present in the macrocycle ligands in one of the crystallographically independent cations in each of [Na(L)][BAr F ] complexes (L = [18]aneO 4 S 2 , [18]aneO 4 Se 2 and [18]aneO 2 S 4 ) and was modelled similarly. H-atoms were placed in geometricallyassigned positions with C-H distances of 0.95 Å (CH) or 0.98 Å (CH 2 ) and refined using a riding model with U iso (H) = 1.2U eq (C). enCIFer was used to prepare material for publication. 16 Preparations General method. M[BAr F ] was suspended in CH 2 Cl 2 (10 mL) and a solution of the macrocycle in CH 2 Cl 2 (5 mL) was added. Complete dissolution occurred and the reaction was stirred for 16 h. After this time the solution was filtered, concentrated to ∼3 mL and layered with n-hexane (20 mL) to form crystals. These were isolated by decanting away the supernatant and drying in vacuo. Specific details for individual complexes are below.

Results and discussion
Coordination of the Group 1 cations to a range of 18-membered oxa-thia and oxa-selena macrocyclic ligands was )] + each contain a singlet, at +0.07 and +1.85 ppm respectively, i.e. very small differences from LiCl in water (δ = 0). This is not unexpected given the small chemical shift range observed for 7 Li (typically ca. 15 ppm). 12 For the sodium complexes, 23 Na NMR spectra (CH 2 Cl 2 ) show a shift of the resonance to higher frequency as the S/Se donor atoms are introduced to the macrocycle (18-crown-6: −14.4 ppm; [18]aneO 4 S 2 : −1.9 ppm; [18] 17 Small positive chemical shifts were also seen for [Na{Me 2 P(CH 2 ) 2 PMe 2 } 3 ] + and [Na{o-C 6 H 4 (PMe 2 ) 2 } 3 ] + , 7 whereas δ 23 Na for solutions of NaBPh 4 with 15-crown-5 in a variety of O-donor solvents are reported to be to low frequency of the reference irrespective of the concentration of the crown ether. 18 The quadrupole moment (Q) for the 133 [18]aneN 6 )] + shows a singlet +54 ppm at 298 K. 20 The large Q values for 39 K and 85 Rb result in fast relaxation in these low-symmetry environments and no resonances were seen. Overall, the spectroscopic data for the complexes reported herein are consistent with coordination of the macrocycles to the alkali metal cations, the complexes being dynamic in solution, most likely through 'ring-whizzing' within the complex cations (it is unlikely that the [BAr F ] − coordination is retained in solution). However, these measurements do not provide unequivocal evidence for coordination of the soft S or Se donor atoms.

X-ray structures and comparisons
The paucity of complexes with thio-or seleno-ether coordination to a Group 1 cation in the literature means that structural authentication of the new complexes was essential to establish their identities. Furthermore, it is difficult to draw comparisons with other structures, and determining the significance of particular metal-ligand interactions is somewhat uncertain. Table 2 provides the sums of the relevant radii, on one hand the sum of the ionic radii of the cations and the covalent radii of the donor atoms (O, S, Se and F) and on the other the sum of the van der Waals radii for the relevant metal-donor atom combinations. Distances close to the former are considered to be 'normal' coordinate bonds, while in identifying weak interactions, for example, between the metal cation and the CF 3 groups from [BAr F ] − anions, we have chosen to include any M⋯X distances at least 0.5 Å below the sum of the van der Waals radii. Although the precise cut-off is somewhat arbitrary, it seems to be a reasonable basis on which to describe the overall coordination in these complexes. It is also pertinent to note that due to the disorder present in Scheme 1 Synthesis of the complexes reported in this work.   (Fig. 1) and anions, with two of each in the asymmetric unit. Each Li cation is six-coordinate with the hexadentate macrocycle, leading to a severely distorted octahedral geometry. The Li-O and Li-S bond distances show a range of values, with d(Li-O) = 2.055(12) to 2.349(13) Å and d(Li-S) = 2.724(11) to 2.788(11) Å. The angles, S1-Li1-S2 = 106.2(4)°and S3-Li2-S4 = 111.3(4)°, whilst the angles involved in the five-membered chelate rings all vary between ∼70-80°, indicating a significant degree of distortion from a regular octahedron. The irregularity of the coordination may in part reflect the poor size match of the 18-membered ring for the small Li + centre, coupled with the packing of the large [BAr F ] − anions around the cations in the crystal lattice.
Substituting two further S donor atoms into the macrocyclic ring, as in [Li( [18]aneO 2 S 4 )][BAr F ], also leads to a structure comprising of discrete cations and anions, with three crystallographically independent, but structurally similar, variants of each in the asymmetric unit. Each Li is six-coordinate, encapsulated by the macrocycle which is folded to accommodate a distorted octahedral geometry at lithium (Fig. 2). The distortion from ideal octahedral is significantly less than in the [18]aneO 4 S 2 analogue above, and the conformation of the coordinated macrocycle has the -S(CH 2 ) 2 O(CH 2 ) 2 S-linkages occupying meridional coordination sites, placing the CCOC torsion angles anti. The Li-O and Li-S distances vary between the different cations, and are ∼2.1 Å and ∼2.6 Å, respectively. The latter appear to be slightly shorter than those in [Li( [18]-aneO 4 S 2 )] + above.
The structure of [Na( [18]aneO 2 S 4 )][BAr F ] is markedly different from its Li analogue above. It crystallises as a 1D chain polymer, with the Na in an eight-coordinate environment (Fig. 5a), and only one centrosymmetric cation and one anion (with crystallographic 2-fold symmetry) in the asymmetric unit. The macrocycle adopts a chair conformation with all four S atoms coordinated and the S 4 donor set planar, d(Na-S) = 2.8823(6), 3.0718(7) Å, with the two oxygen atoms above and below that plane, d(Na-O) = 2.5526(13) Å. Two weak Na⋯F interactions (2.8766(13) Å) from bridging [BAr F ] − anions on opposite sides of the macrocycle give a distorted dodecahedral geometry overall at sodium, and give rise to the polymeric chain structure (Fig. 5b).
To provide a benchmark comparison for the mixed donor macrocyclic complexes in this work, we also prepared and determined the structure of [Na (18-crown-6)][BAr F ]. The structure also shows a 1D chain polymer with eight-coordinate Na.
There are two 50% occupancy (centrosymmetric) Na environments in the asymmetric unit, one of which (Na2-centred cation) shows severe rotational disorder of the macrocycle, while the other refines much better and is therefore the focus of the structural description and illustrated in Fig. 6a and b. The crown ether provides hexagonal planar coordination at Na, with irregular Na-O bond distances spanning >0.3 Å, and with a slightly puckered conformation as expected (<O-Na-O ∼ 62-65°), with two axial Na⋯F interactions (2.435(4) Å), similar motifs are evident in other salts containing the sodium-18-crown-6 cation. 1 The Na⋯F distances are very much shorter than in the mixed donor macrocyclic cations described above.
[K( [18] (Fig. 7). All of the bond distances at K1 are elongated by ca. 0.1 Å compared to the Na analogue. This is less than expected based purely on the difference in the ionic radii of the metal ions (0.33 Å for CN = 8), possibly reflecting a better size match between K + and the [18]aneO 2 S 4 binding cavity (although caution is required to avoid over-interpretation of such differences given that there is some disorder in the anion).
The structure of [K( [18]aneO 4 S 2 )][BAr F ] is formed of a 1D chain polymer with three crystallographically independent cations in the asymmetric unit (as well as three [BAr F ] − anions). The K centres are eight-coordinate, through hexadentate endocyclic coordination of the macrocycle, with d(K-O) ∼ 2.7 Å and d(K-S) ∼ 3.2 Å, with two quite short K-F interactions (each ∼2.7 Å) completing the coordination environment (Fig. 8). The centrosymmetric K1-and K3-centred cations have significant K⋯F interactions on opposite sides of the macrocycle, while in the K2-centred cation the K⋯F interactions lie mutually cis, and <S3-K2-S2 = 154.90(6)°. Some puckering of the rings is evident from the angles subtended at K, which are all ∼64°.
[K( [18]aneO 4 Se 2 )][BAr F ] (Fig. 9) is isomorphous and isostructural with the tetraoxa-dithia analogue, and presents the first known complex containing potassium-selenoether coordination, d(K-Se) ca. 3.3 Å.  The structure of [Rb( [18]aneO 4 S 2 )][BAr F ] is also a 1D chain polymer, very similar to the K analogue, with the macrocycle hexadentate in each form of the cation, d(Rb-S) ∼ 3.3 Å (Fig. 10), although the crystal is not isomorphous. All the Rb-F distances are comparable to the Rb-O distances, indicating significant interactions that lie well within the sum of vdW radii. The geometry at Rb1 is higher than in the K analogue, as there are now three CF 3 groups interacting with the Rb centre which appears to be ten-coordinate.
The Rb2 (and Rb3: two half-occupancy centrosymmetric Rb centres in the asymmetric unit) are both 8-coordinate. The macrocycle donor set is closer to planar than in the K analogue.
Finally, the structure of [Cs( [18]aneO 4 S 2 )][BAr F ] (Fig. 11) shows one cation and one anion in the asymmetric unit, and forms a 2D sheet polymer. The hexadentate macrocycle occupies one face of the Cs + cation (Cs-S ∼ 3.5 Å), with four CF 3 groups (each from a different [BAr F ] − anion) also coordinated through the other face, although the precise coordination at Cs cannot be confirmed due to disorder of the CF 3 groups. There is also one longer Cs⋯F interaction through the centre of the macrocycle of ∼4.2 Å.