
==== Front
Inorg Chem
Inorg Chem
ic
inocaj
Inorganic Chemistry
0020-1669
1520-510X
American Chemical Society

39160773
10.1021/acs.inorgchem.4c01890
Article
Experimental and Computational 77Se NMR Spectroscopic Study on Selenaborane Cluster Compounds
https://orcid.org/0000-0003-3615-1938
Bould Jonathan *
https://orcid.org/0000-0002-6161-6592
Londesborough Michael G. S.
https://orcid.org/0000-0002-9779-0576
Tok Oleg L.
Institute of Inorganic Chemistry of the Czech Academy of Sciences, Husinec-Řež 250 68, Czech Republic
* Email: bould@iic.cas.cz.
20 08 2024
02 09 2024
63 35 1618616193
07 05 2024
12 08 2024
03 08 2024
© 2024 The Authors. Published by American Chemical Society
2024
The Authors
https://creativecommons.org/licenses/by/4.0/ Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/).

Calculated and measured 77Se nuclear magnetic resonance (NMR) chemical shift data on a diverse collection of 13 selenaborane cluster compounds, containing a total of 19 selenium centers, reveals a correlation between chemical shifts and the intracluster coordination of selenium atoms within their borane frameworks. A plot of the measured against calculated 77Se NMR chemical shifts shows an approximately linear relationship that can serve as a predictive tool in assessing the chemical shift range in which a selenium vertex from a particular compound might be expected to be found, thereby reducing expensive experimental time. Furthermore, the relative chemical shifts between selenium vertices in clusters containing more than one selenium atom are consistent across the range, thus allowing the assignment of the selenium resonances with a high degree of confidence even in relatively low-level density functional theory calculations. A new macropolyhedral 20-vertex selenaborane Se2B18H20 (A) is also reported.

Calculated 77Se chemical shifts are correlated with measured 77Se NMR chemical shifts for a series of macropolyhedral selenaboranes and related selenium containing boron compounds with up to 3 selenium atoms. NMR techniques to determine the assignment of selenium resonances in large borane cluster species are not experimentally practical. The correlation enables the assignment of the selenium vertices to their cluster positions.

GrantovÃ¡ Agentura CeskÃ© Republiky 10.13039/501100001824 23-07563S document-id-old-9ic4c01890
document-id-new-14ic4c01890
ccc-price
==== Body
pmcIntroduction

Selenium-77 nuclear magnetic resonance (NMR) spectroscopy plays a useful role in the characterization of compound in both organoselenium chemistry and bioorganic chemistry, providing insights into structure and compound identity.1−3 For example, it has proven useful in enabling bioorganic selenametabolite compounds to be individually identified by their 77Se chemical shifts, thus providing a 77Se ′fingerprint′.4 In inorganic carboranyl boron cluster compounds, the presence of selenium has been used to assess the relative basicity of carboranylphosphines via the P–Se coupling constants.5 We, however, are interested in selenium chemical shifts in selenaborane macropolyhedral cluster compounds and the use of quantum chemical calculations to predict their chemical shifts.

Binary boron hydride compounds (boranes), a group of inorganic polyhedral molecules comprising clusters of boron and hydrogen atoms, display a diversity of structures surpassed only by the hydrocarbons.6,7 Borane clusters may incorporate main group elements that subrogate cluster {HB} vertices, often leading to an alteration in the cluster properties.8−10 Examples are found where Group 14, 15, and 16 elements such as carbon,10 nitrogen,9 and the chalcogens sulfur, selenium, and tellurium have been incorporated in borane and metallaborane clusters.11−18 In the case of selenium and sulfur, these have also been combined in so-called macropolyhedral clusters, which are defined as “borane compounds that contain two or more cages, with individual cages that are joined or fused to each other with two or more atoms held in common”.19 The synthesis and characterization of a number of new anionic macropolyhedral selenaboranes have been described,20,21 and, more recently, the photophysical properties of their luminescent neutral conjugate acids together with other luminescent macropolyhedral thiaboranes have also been reported.22 In terms of NMR spectroscopy, these selenaborane compounds were characterized by their 11B and 1H spectra. The nuclear spin-half property of selenium-77, its 7.6% natural abundance, and gyromagnetic ratio of 19.071523 × 10–7 rad·s–1·T–1 allow an additional and easily available metric using a routine single-pulse sequence for the characterization of selenaborane clusters, which can potentially deliver additional structural information. Nevertheless, historically, the measurement of 77Se chemical shifts during the characterization of selenaborane species has not been routine,17,23−30 and it has thus hitherto received little attention, although a recent publication has described a similar approach to our work reported herein, with a pairing of measured and calculated 77Se NMR chemical shifts in a number of perchlorinated monoselenaborane clusters.31 There is also a number of compounds that contain both B–H units, chalcogens and metal units, such as Mo or Fe, in which 77Se chemical shifts have been measured, but they feature cubane-type or other structural motifs that do not resemble conventional borane clusters based usually on an icosahedron.15,16,32 They thus fall outside the scope of the work reported here.

In selenaborane compounds with only one selenium vertex, the assignment of the selenium resonance is clear. However, the assignments are not so straightforward in the macropolyhedral and other selenaborane species reported here, which contain two or three selenium atoms per molecule. There are several NMR techniques for assigning 11B and 1H resonances in borane clusters to their cluster positions, and they typically include different variations of 1D experiments (coupled, broad-band or selective decoupled, etc.) together with 2D methods such as 1H–11B HMQC (heteronuclear multiple-quantum correlation) and 1H–11B HSQC (heteronuclear single-quantum correlation) and 11B–11B-COSY (homonuclear correlation spectroscopy) methods. However, there are no 1D or 2D correlation NMR techniques suitable for assigning the positions of selenium vertices in heteroborane species holding more than one selenium atom. This is because both 1H and 11B resonances are too broad to observe selenium-77 satellites or to apply the correlation methods based on long-range 1H–77Se or 11B–77Se couplings, which would enable a direct assignment of the boron resonances adjacent to the selenium vertices. We have thus resorted to quantum chemical calculations to investigate the possibility of achieving a suitably close correlation between calculated and measured values in order to assign the selenium resonances to their positions in selenaboranes. Herein, we endeavor to collate and describe the measured and calculated 77Se NMR chemical shifts of this range of selenaboranes, limited to those in which selenium acts as a vertex in the borane cluster rather than, for example, an exo-polyhedral substituent replacing an exo-terminal hydrogen atom and also where selenium is the only cluster heteroelement in order to eliminate the complications that will ensue from the inclusion of, for example, heavier ligated transition metal moieties mentioned above. We show how these collective data can be used to predict the region in which to expect the 77Se NMR signals to be found in new selenaboranes. This approach has been used previously for correlations between 11B calculated and measured values33 and a range of organic and inorganic selenium compounds34,35 but has not previously been applied to selenaboranes. Measured 77Se resonances are very sensitive to the local surroundings such that they can be spread over a long range of ca. 3000 ppm,36−38 and thus they can be time-consuming to locate, especially in weaker samples. Consequently, there is utility in accurately calculating the potential chemical shift range in which a particular selenium atom might be expected to be found.

Results and Discussion

This paper deals primarily with the comparison of the calculated and measured 77Se chemical shifts of the previously reported neutral and anionic selenaborane cluster compounds of known structure, as shown in Chart 1. Nevertheless, we first describe the characterization of a previously unreported new neutral selenaborane Se2B18H20 (Compound A). Data for A were not included in our recent paper on the luminescent properties of chalcogen-containing macropolyhedral species,22 as the low amounts of the compound available were not sufficient for full photophysical investigation. It is, however, useful to demonstrate how a comparison of the measured and calculated Se-77 chemical shifts can be used to support the proposed structure.

Compound A is produced almost quantitatively from the protonation of a low-yield (3%) side product, the [Se2B18H19]− anion, formed in the reaction between syn-B18H22 and elemental selenium.21 This is in contrast to the higher yield (48%) equivalent reaction between elemental sulfur and syn-B18H22.39 Similarly to the reaction for [S2B18H19]−, the 20 vertex macropolyhedral species Se2B18H20A may be prepared from [Ph4P][Se2B18H19] by the addition of H2SO4 or CF3COOH to dichloromethane solutions of the anion (Scheme 1). An almost quantitative formation of protonated compound A was observed by boron-11 NMR spectroscopy on acidification of the anion (Figure S1) with H2SO4. The thiaborane analogue has been described, and its structure deduced from NMR spectroscopy allied with density functional theory (DFT) calculation.40 We similarly have only been able to characterize the cluster compound by 11B, 11B{1H}, 11B{1H selective}, and 1H-11B HMQC spectroscopy, with the addition of 77Se NMR spectroscopy, and by comparison of these with the thiaborane analogue. Our attempts to obtain single crystals of both A and the sulfur analogue suitable for X-ray diffraction analysis were unsuccessful. The 11B and 1H NMR data for A are listed in Table 1 together with the boron chemical shift data for S2B18H20, and they show an excellent correspondence between the measured sulfur and selenium species and the calculated boron NMR chemical shifts for A. The 11B{1H} spectrum for A and the 77Se spectrum are shown in Figure 1. Figure 2 shows an ORTEP-type drawing of the DFT calculated structure together with the cluster numbering. The 77Se NMR spectrum in Figure 1 shows two selenium resonances labeled Se(9′) and Se(9). These were assigned by a comparison of the calculated and measured chemical shifts. The means by which we arrived at these assignments are described next.

Table 1 Measured Proton and Boron-11 NMR Data for Se2B18H20 (A) at 293 K in CDCl3 Solution with B3LYP/6-31+G(d,p)/GIAO Calculated Chemical Shifts in Square Brackets and Together with Measured δ(11B) NMR Comparison Data for S2B18H2040

assign	δ(11B)/ppm	δ(1H)/ppm	δ(11B)/ppm of S2B18H20	
B(2′)	+17.3 [+16.7]	+4.27	+15.9	
B(2)	+14.6 [+14.4]	+4.91	+15.3	
B(4)	+10.1 [+12.6]	+4.19	+9.1	
B(5′)	+10.1 [+12.1]	+3.73	+11.1	
B(8′)	+9.0 [+11.9]	+3.88	+7.3	
B(11′)	+5.7 [+6.3]	+3.46	+5.6	
B(4′)	–1.6 [−0.4]	+3.19	–1.9	
B(7)	–3.5 [−1.4]	+2.86	–5.1	
B(10′)	–5.8 [−5.8]	+2.69	–6.0	
B(8)	–9.6 [−6.2]	+2.62	–8.5	
B(10) B(1′)	–11.6(2) [−8.5, −11.3]	+3.32, +2.86	–11.6(2)	
B(6)	–12.3 [−9.8]	---a	–13.1a	
B(1)	–20.2 [−19.0]b	+2.82	–19.5	
B(5)	–20.4 [−18.7]b	+1.17	–19.5	
B(3′)	–21.2 [−20.6]	+1.57	–22.2	
B(6′)	–25.7 [−26.0]	+1.56	–24.2	
B(3)	–35.5 [−34.9]	+1.75	–34.9	
μH(5,10)	 	+0.57	+1.00	
μH(7,8)	 	–1.20	–0.88	
μH(10′,11′)	 	–1.62	–1.14	
a Commo-boron position and therefore no attached proton.

b It may be noted that the ordering of calculated boron chemical shifts is reversed compared to the measured values. The 1H–11B HMQC spectrum (Figure S2) shows that the bridging hydrogen resonance at +0.57 ppm is coupled to the boron resonance at −20.4 ppm as would be expected if the boron resonance is due to vertex B(5). Some cross peaks are not found, but these were located by selectively decoupled boron in the proton spectra, 1H{11Bselective}, as shown in Figure S3. Additionally, as we have noted before,41 it is often possible to differentiate the assignments of close boron resonances from calculation by also looking at the calculated values for their individual directly attached exo-terminal proton resonances. Thus, for B(5)-H, the calculated value is +1.17 ppm compared to that for B(1)-H, where it is +2.93 ppm. These nicely match the measured values from the HMQC spectrum of +1.17 and +2.82 ppm, respectively, thereby supporting the assignments given in the table.

Scheme 1 Protonation of [Ph4P][Se2B18H19] (B) to Afford Se2B18H20 (A)

Figure 1 (Upper) 11B-{1H} NMR spectrum of Se2B18H20, A. All resonances are doublets in the 11B spectrum except for the singlet resonance due to the commo-boron atom linking the two subclusters, as denoted by an asterisk. (Lower) 77Se NMR spectrum of A.

Figure 2 ORTEP-type diagram of the DFT-calculated structure of Se2B18H20A, showing the cluster numbering.

Calculations

Precisely calculated values for heavy elements such as 77Se may ideally include relativistic corrections using routines other than DFT methods, but these would require considerable computing power for even simple selenium-containing compounds.36 GIAO-MP2 methods have been used to good effect in the calculation of 77Se chemical shieldings.34 These, however, are also computationally expensive, and we therefore compare them to less expensive DFT methods that may be more routinely used in the characterization of selenaborane compounds. Here, we parallel lower-level DFT calculated isotropic shielding constants using B3LYP and mPW1PW91 functionals to those of MP2 (2nd order Møller–Plesset perturbation theory). In all cases, use the same 6-31+G(d,p) basis set for the main group elements B, H, and Cl and with the Binning and Curtiss 962 + d polarization basis set for Se, as used previously by Buehl et al.34 The calculated chemical shift values presented in Table 2 are derived from linear regression analyses of the calculated isotropic shielding relative to the calculated value for the dimethylselenide reference at the appropriate level versus the measured chemical shifts. Plots of the data are shown in Figure 3 together with the linear regression parameters. The three methods can be seen to produce very similar values for R2, the coefficient of determination, and the two relatively low-cost DFT methods, which are not significantly different from the more computationally costly MP2 calculations. The mPW1PW91/6-31+G(d,p) method shows a good correlation between measured and calculated values, and these will be used in further discussions.

Chart 1 Schematic Structures of the Measured Selenaboranes Listed in Table 2

Table 2 Measured and Calculated 77Se NMR Chemical Shifts in CDCl3

 	 	4/5-connectedb	3-connectedc	
ref	compounda	meas	B3LYPd	mPW1PW91	MP2d	meas	B3LYPd	mPW1PW91	MP2d	
this worke	A	Se2B18H20	+119	+118	+127	+138	–79	–71	–55	–77	
(21)	B	[Se2B18H19]	+62	+35	+44	+86	–516	–493	–514	–508	
(21)	C	[Se2B17H18]	 	 	 	 	+35	–4	+8	+20	
(22)	D	Se2B17H17	+135	+110	+129	+185	+122	+94	+97	+119	
(21)	E	[SeB18H21]	 	 	 	 	–163	–132	–126	–128	
(21)	F	[SeB18H19]	+304	+321	+280	+301	 	 	 	 	
(22)	G	SeB18H20	+322	+312	+303	+326	 	 	 	 	
(22)	H	SeB17H19	 	 	 	 	+474	+476	+493	+457	
(20)	I	[Se3B18H21]	 	 	 	 	–286	–295f	–285f	–290f	
 	 	 	 	 	 	 	+97	+60g	+63g	+52g	
 	 	 	 	 	 	 	+158	+247h	+239h	+221h	
this worke	J	[SeB10H11]	+105	+109	+82	+85	 	 	 	 	
this worke	K	SeB10H12	+100	+91	+93	+86	 	 	 	 	
this worke	L	SeB11H11	+254i	+244	+251	+223	 	 	 	 	
(31)	M	SeB11Cl11	–31i	–13	–23	+1	 	 	 	 	
(31)	N	SeB5Cl5	–146	–144	–147	–140	 	 	 	 	
a Square brackets indicate that the compound is monoanionic. See Chart 1 for schematic structures of the compounds and Figures 1 and S4–S16 for the77Se measured spectra.

b 4-Connected selenium on an 11-vertex subcluster.

c 3-Connected selenium on a 10-vertex subcluster.

d Chemical shift values estimated from the linear regression analysis shown below in Figure 3.

e The [SeB10H11]− anion25 was obtained as a byproduct in the synthesis of [Se2B17H18]−,21 and its conjugate acid, SeB10H12, was obtained by acidification of the anion with H2SO4. SeB11H11 was donated by Josef Holub.42

f Se(1), see Chart 1.

g Se(2), see Chart 1.

h Se(3), see Chart 1.

i 5-Connected selenium.

Figure 3 Plots of measured versus calculated δ(77Se) chemical shifts at the DFT/B3LYP, DFT/mPW1PW91-GIAO, and MP2 levels. The lines represent the linear regression analyses δcalc = A × δexp + B with B3LYP, A = 0.886, B = 66, R2 = 0.983; mPW1PW91, A = 0.912, B = 23, R2 = 0.988; MP2, A = 0.925, B = −9, R2 = 0.986. The data point labeled I is the most prominent outlier point. Numerical data are listed in Tables S1–S3.

Although there is no way to definitely assign the calculated values to the measured values in the multiselenium compounds, the close conformity of the calculated and measured values in the compounds containing a single selenium vertex, including the perchlorinated species SeB11Cl11M and SeB5Cl5N, allows us a large degree of confidence in the assignments in those macropolyhedral species where the identities of the measured selenium resonances cannot be directly assigned. The differences in the chemical shifts between the sites in the macropolyhedral species are, in most cases, considerably greater than the standard deviations in the calculated values. This is, however, currently a limited set of data.

In the three methods, there is one prominent outlier point (I in Figure 3). This arises from the [(Se2B9H10)(SeB9H11)]– anion, compound I in Chart 1. Here, the 3-connected Se(3), vertex held on a nido cluster, affords a measured value of δ(77Se) + 158 ppm and a calculated value of +239 ppm, making it the selenium atom presenting the largest deviation for all three methods. In contrast, the Se(1) held on an arachno cluster in the same molecule gives δ(77Se) −286 ppm, which is very close to the calculated value of −285 ppm, and also a bridging Se(2) center with very close measured and calculated chemical shifts of +97 and +63 ppm, respectively. This is an indication of the large effect that the local cluster environment can have on the shielding around the selenium centers and that calculated values may potentially vary quite widely, even in the same molecule. The two clusters in [(Se2B9H10)(SeB9H11)]− are linked by a two-electron, two-center single bond, suggesting that there can be free rotation around the linkage. This molecular flexibility may introduce effects not well modeled by the calculated static structures. Nevertheless, in nearly all cases, each calculational method produces the chemical shifts in the same order as the measured values. Thus, the ordering of the higher and lower field resonances in the measured macropolyhedral selenaboranes is always mirrored by the calculations. This is also true for compound I above. The only exception is in the 11-vertex nido clusters for the mPW1PW91/6-31+G(d,p) level, where the ordering of the very close measured values for the anion [SeB10H11]−J and SeB10H12K at +105 and +100 ppm is reversed in the calculated chemical shifts (+82 and +93 ppm, respectively). This indicates that the predictions for separate molecules with very close chemical shifts are not reliable. Nevertheless, the predictions are still sufficiently close to the observed chemical shifts to allow the resonances to be located easily during the measurement.

Overall, with this small sample of compounds, the anionic species seem to appear generally at higher field than the neutral species as shown in the A/B, G/F, and K/J conjugate acid/base pairs.

Figure 4 illustrates the distribution of the selenium resonances in polyhedral boron hydride species A to L. The perchlorinated closo species M and N are not considered here, as they constitute a separate subgroup. From this presentation of the data, two trends are revealed. First, the measured 77Se chemical shifts in the nido subclusters with a 4-connected Se vertex span a smaller range (from +62 to +322 ppm) compared to the subclusters with a 3-connected Se vertex, which span a much larger range of almost a 1000 ppm (from +474 ppm in neutral SeB17H19, H, to −516 ppm in anionic [Se2B18H19]−B). Second, the data so far suggest that selenium vertices on the nido clusters and subclusters are to lower field than that for the arachno subclusters.

Figure 4 Schematic illustration of the distribution of 77Se resonances in selenaborane species. See Chart 1 for compound identity.

Also noteworthy is the resonance in the 20-vertex [Se2B18H19]− anion B at −516 ppm, which is 230 ppm more shielded than the closest next resonance—the arachno 3-connected Se(1) vertex in I (−286 ppm). The extent of this difference led us to consider its reason. Thus, in B, one subcluster contains a rare 6-connected boron vertex,21,43,44 and the subcluster could be regarded as being based geometrically on a closo-14-vertex tetradecahedron45,46 of either arachno 12-vertex constitution with 2 missing vertices or of hypho 11-vertex geometry based on 3 missing vertices (Chart 2a) depending on whether or not the boron atom labeled B is included in or excluded from the subcluster vertex count. In both of these, the selenium vertex is in an antipodal position with respect to the 6-connected boron in the tetradecahedron. We consequently hypothesized that the chemical shift might be due to the antipodal effect47 of the boron vertex, and we therefore calculated the chemical shift of selenium in a hypothetical closo-SeB13H13 cluster using the mPW1PW91 level regression analysis. However, as shown in Chart 2b, the chemical shift of +145 ppm is in the same region as for closo-SeB11H11 (L) and no extreme effect of the unusual boron vertex is evident. Interestingly, the chemical shift of the 4-connected selenium vertex directly adjacent to the boron atom in the dicommo linkage that is protonated on the acidification of [Se2B18H19]− (see Scheme 1) does not undergo a large chemical shift change (+62 to +119 ppm), whereas the more remote 3-connected selenium changes from −79 to −516 ppm. This indicates that the second subcluster has a large influence on the electronic environment of the selenium. Separate calculations of the δ(77Se) for the hypothetical arachno and hypho subcluster geometries, Chart 2c,d, respectively, show a much better correlation between the 11-vertex hypho constitution and compound B (see Chart 2), suggesting this to be the better description of its subcluster geometry and may account for its increased shielding.

Chart 2 Structural Considerations of the [Se2B18H19]− Anion (B). (a) Measured Chemical Shifts and (b–d) Calculated Chemical Shifts at the mPW1PW91 Level.

Finally, as we noted earlier in the description of the characterization of Se2B18H20A, primarily by 11B and 1H NMR spectroscopy and their comparison to those of S2B18H20, the prediction of the selenium chemical shifts by all three methods gives very close correlations to the measured values, and they therefore give independent confirmation of the proposed structures of both Se2B18H20 and S2B18H20.

Conclusions

This work indicates that fast and computationally inexpensive lower-level quantum chemical calculations are sufficiently accurate to enable the assignment of measured data in macropolyhedral selenaborane species. There are, however, currently only a limited number of examples from which to make this assessment, and we hope to expand this data set with further work. Nevertheless, being able to predict 77Se NMR chemical shifts in selenaborane cluster compounds offers several benefits.1 The chemical shift of the selenium nucleus in a selenaborane cluster compound can provide information about its molecular structure. Accurate prediction of these chemical shifts allows researchers to better understand the arrangement of atoms within the cluster, as well as subcluster geometries (nido, arachno, etc.).

2 Accurately predicted chemical shifts enable the position of 77Se resonances to be more efficiently located in experimental measurements. Indeed, in the final sample we measured, SeB18H20, for which only a small amount of material was available, requiring a long accumulation time, we looked in the predicted region of zero to +400 ppm and found the measured resonance at +322 ppm (calculated: +303 ppm).

3 Reliable prediction of 77Se NMR chemical shifts aids the interpretation of experimental spectra, permitting the assignment of specific signals to different structural motifs within selenaborane cluster compounds. This may aid in the identification and characterization of these compounds in complex mixtures or reaction intermediates.

Experimental Section

Caution

Although selenium is a biologically useful trace element, it is toxic,48 and selenium-containing compounds should be handled accordingly.

NMR Spectroscopy

NMR spectra were recorded on a JEOL ECZ 600 R (14.1 T) spectrometer using 77Se, 11B, 11B{1H}, 1H, 1H{11B(broadband)}, 1H{11B(selective)}, and HMQC (heteronuclear multiple-quantum correlation) techniques. NMR spectra of all compounds were measured in a CDCl3 solution. 11B chemical shifts given relative to BF3·OEt2, δ11B = 0.0 ppm for Ξ (11B) = 32,083,971 Hz. 77Se chemical shifts are reported relative to SeMe2, δ(77Se) = 0.0 ppm for Ξ (77Se) = 19,071,523 Hz.

The 77Se NMR spectra were measured using a standard single-pulse sequence (available from the spectrometer library) with a 90° pulse length and relaxation delay of 0.1–0.2 s. The line widths of the 77Se resonances were in the range of 200–300 Hz, and the spectra were recorded with an FID resolution of 3–4 Hz. Due to the absence of the hydrogen atoms attached to the Se atom, the spectra were acquired without proton decoupling.

Computational Details

Calculations were performed using Gaussian16 package.49 For the DFT/B3LYP methodology, the 6-31+G(d,p) basis sets for B, Cl, and H were used, and the Binning and Curtiss 962 + d polarization basis set for Se was taken from Basis Set Exchange.50 The higher level MP2 calculations were carried out using the same basis sets. The polarizable continuum model was implemented with CHCl3 solvation. Frequency analyses to confirm the true minima were performed at the appropriate level.

Preparation of Se2B18H20 (A)

The compound was prepared by adding excess concentrated H2SO4 to a CH2Cl2 solution of [Ph4P][Se2B18H19] in a small sample tube. The mixture was shaken, then allowed to settle, and the upper CH2Cl2 layer was decanted. The solvent was removed under a stream of nitrogen and redissolved in CDCl3 for NMR spectroscopic measurement.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.4c01890.Boron and proton NMR spectra for compound A, plots of 77Se NMR spectra for those compounds measured by the authors, tables of calculated chemical shieldings versus measured chemical shifts, and tables of calculated Cartesian atomic coordinates (PDF)

Supplementary Material

ic4c01890_si_001.pdf

Author Contributions

The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.

Acknowledgments

This work was supported by the Czech Science Foundation, Project no. 23-07563S. Computational resources were provided by the e-INFRA CZ project (ID:90254), supported by the Ministry of Education, Youth, and Sports of the Czech Republic.
==== Refs
References

Jain V. K. . In Organoselenium Compounds in Biology and Medicine: Synthesis, Biological and Therapeutic Treatments; Jain V. K. , Priyadarsini K. I. , Eds.; The Royal Society of Chemistry, 2017; pp 1–33.10.1039/9781788011907-00001.
Struppe J. ; Zhang Y. ; Rozovsky S. 77Se Chemical Shift Tensor of L-Selenocystine: Experimental NMR Measurements and Quantum Chemical Investigations of Structural Effects. J. Phys. Chem. B 2015, 119 (9 ), 3643–3650. 10.1021/jp510857s.25654666
Silva M. S. ; Alves D. ; Hartwig D. ; Jacob R. G. ; Perin G. ; Lenardão E. J. Selenium-NMR Spectroscopy in Organic Synthesis: From Structural Characterization Toward New Investigations. Asian J. Org. Chem. 2021, 10 (1 ), 91–128. 10.1002/ajoc.202000582.
Suzuki N. ; Ogra Y. . In Metallomics: Recent Analytical Techniques and Applications; Ogra Y. , Hirata T. , Eds.; Springer: Japan, Tokyo, 2017; pp 147–155.10.1007/978-4-431-56463-8_7.
Benton A. ; Durand D. J. ; Copeland Z. ; Watson J. D. ; Fey N. ; Mansell S. M. ; Rosair G. M. ; Welch A. J. On the Basicity of Carboranylphosphines. Inorg. Chem. 2019, 58 (21 ), 14818–14829. 10.1021/acs.inorgchem.9b02486.31638782
Nandi C. ; Kar K. ; Roy A. ; Ghosh S. Metallaboranes and metallaheteroboranes: An overview of single-cage and condensed polyhedral clusters. In Adv. Inorg. Chem.; Chatterjee D. , van Eldik R. , Eds.; Academic Press, 2023; Vol. 81 , pp 41–93.10.1016/bs.adioch.2022.09.001.
Kennedy J. D. In Big Borane Assemblies, Macropolyhedral Species and Related Chemistry, Boron: The Fifth Element; Hnyk D. , McKee M. , Eds.; Springer: Heidelberg, New York, Dordrecht and London, 2015; Chapter 6, Vol. 20 , pp 139–180, 10.1007/978-3-319-22282-0_6.
Todd L. J. ; Siedle A. R. NMR studies of boranes, carboranes and hetero-atom boranes. Prog. Nucl. Magn. Reson. Spectrosc. 1979, 13 (2 ), 87–176. 10.1016/0079-6565(79)80001-1.
Wesemann L. s- and p-Block Heteroboranes and Carboranes. Compr. Organomet. Chem. III 2007, 3 , 113–131. 10.1016/B0-08-045047-4/00044-3.
Grimes R. N. Carboranes, 3rd ed.; Elsevier: Oxford, UK, 2016.
Haridas A. ; Bedajna S. ; Ghosh S. Substitution at B-H vertices of group 5 metallaborane clusters. J. Organomet. Chem. 2022, 961 , 122250 10.1016/j.jorganchem.2021.122250.
Nandi C. ; Roy A. ; Kar K. ; Cordier M. ; Ghosh S. Cluster Growth Reactions: Structures and Bonding of Metal-Rich Metallaheteroboranes Containing Heavier Chalcogen Elements. Inorg. Chem. 2022, 61 (42 ), 16750–16759. 10.1021/acs.inorgchem.2c02601.36228081
Pathak K. ; Nandi C. ; Ghosh S. Metallaheteroboranes with group 16 elements: Aspects of synthesis, framework and reactivity. Coord. Chem. Rev. 2022, 453 , 214303 10.1016/j.ccr.2021.214303.
Chakrahari K. K. ; Thakur A. ; Mondal B. ; Ramkumar V. ; Ghosh S. Hypoelectronic Dimetallaheteroboranes of Group 6 Transition Metals Containing Heavier Chalcogen Elements. Inorg. Chem. 2013, 52 (14 ), 7923–7932. 10.1021/ic400432v.23819867
Geetharani K. ; Bose S. K. ; Sahoo S. ; Ghosh S. A Family of Heterometallic Cubane-Type Clusters with an exo-Fe(CO)3 Fragment Anchored to the Cubane. Angew. Chem., Int. Ed. Engl. 2011, 50 (17 ), 3908–3911. 10.1002/anie.201008101.21425424
Sahoo S. ; Mobin S. M. ; Ghosh S. Direct insertion of sulfur, selenium and tellurium atoms into metallaborane cages using chalcogen powders. J. Organomet. Chem. 2010, 695 (7 ), 945–949. 10.1016/j.jorganchem.2009.11.025.
Friesen G. D. ; Barriola A. ; Daluga P. ; Ragatz P. ; Huffman J. C. ; Todd L. J. Chemistry of dithia-selenathia-and diselenaboranes. Inorg. Chem. 1980, 19 (2 ), 458–462. 10.1021/ic50204a035.
Bairagi S. ; Chatterjee D. ; De A. ; Cordier M. ; Roisnel T. ; Ghosh S. Syntheses, structures, and bonding of boron containing niobium and ruthenium clusters stabilized by chalcogens. J. Organomet. Chem. 2024, 1012 , 123126 10.1016/j.jorganchem.2024.123126.
Beckett M. A. ; Brellochs B. ; Chizhevsky I. T. ; Damhus T. ; Hellwich K.-H. ; Kennedy J. D. ; Laitinen R. ; Powell W. H. ; Rabinovich D. ; Viñas C. ; Yerin A. Nomenclature for boranes and related species (IUPAC Recommendations 2019). Pure Appl. Chem. 2020, 92 (2 ), 355–381. 10.1515/pac-2018-0205.
Bould J. ; Tok O. ; Clegg W. ; Londesborough M. G. S. ; Litecká M. ; Ehn M. The metal-mediated coupling of the diselenaundecaborate anion [Se2B9H10]−. Inorg. Chim. Acta 2023, 547 , 121341 10.1016/j.ica.2022.121341.
Bould J. ; Londesborough M. G. S. ; Litecká M. ; Macías R. ; Shea S. L. ; McGrath T. D. ; Clegg W. ; Kennedy J. D. Macropolyhedral Chalcogenaboranes: Insertion of Selenium into the Isomers of B18H22. Inorg. Chem. 2022, 61 (4 ), 1899–1917. 10.1021/acs.inorgchem.1c03018.35049289
Bould J. ; Ehn M. ; Tok O. ; Bavol D. ; Kučeráková M. ; Clegg W. ; Litecká M. ; Lang K. ; Kirakci K. ; Londesborough M. G. S. Expanding Luminescence Horizons in Macropolyhedral Heteroboranes. Angew. Chem., Int. Ed. Engl. 2024, 63 , e202401872 10.1002/anie.202401872.38400832
Hnyk D. ; Bühl M. ; Holub J. ; Hayes S. A. ; Wann D. A. ; Mackie I. D. ; Borisenko K. B. ; Robertson H. E. ; Rankin D. W. H. Molecular Structures of arachno-Decaborane Derivatives 6,9-X2B8H10 (X = CH2, NH, Se) Including a Gas-Phase Electron-Diffraction Study of 6,9-C2B8H14. Inorg. Chem. 2006, 45 (15 ), 6014–6019. 10.1021/ic060296v.16842008
Binder H. ; Söylemez S. ; Stöckle R. ; Pfitzner A. ; Hofmann M. ; Schleyer P. v. R. Thia- und Selena-arachno-undecaboran 6,7-μ-(CH3E)B10H13 Kristallstruktur von arachno-6,7-μ-(CH3Se)B10H13 Theoretische Untersuchungen der Molekülstrukturen und 11B-NMR-Verschiebungen von arachno-6,7-μ-(CH3E)B10H13. Z. Anorg. Allg. Chem. 1997, 623 (7 ), 1157–1162. 10.1002/zaac.19976230725.
Reed D. ; Ferguson G. ; Ruhl B. L. ; Dhubhghaill O. N. ; Spalding T. R. The formation of the [7-SeB10H11]− anion from 1-SeB11H11 and the structure of the anion studied by boron-11 COSY NMR and x-ray crystallography. Polyhedron 1988, 7 (1 ), 17–23. 10.1016/S0277-5387(00)81176-6.
Ferguson G. ; Parvez M. ; MacCurtain J. A. ; Dhubhghaill O. N. ; Spalding T. R. ; Reed D. Reactions of heteroboranes. Synthesis of [2,2-(PPh3)2-1,2-SePtB10H10].CH2Cl2, its crystal and molecular structure and that of SeB11H11. J. Chem. Soc., Dalton Trans. 1987, (4 ), 699–704. 10.1039/DT9870000699.
Friesen G. D. ; Kump R. L. ; Todd L. J. Preparation and chemistry of the B9H12Se– and B9H12Te– ions. Inorg. Chem. 1980, 19 (6 ), 1485–1488. 10.1021/ic50208a012.
Friesen G. D. ; Todd L. J. Insertion of selenium, tellurium, or arsenic atoms into borane cage compounds using element oxide reagents. J. Chem. Soc., Chem. Commun. 1978, (8 ), 349–350. 10.1039/c39780000349.
Friesen G. D. ; Barriola A. ; Todd L. J. ChemInform Abstract: Syntheses of new selanaboranes using sodium polyselenide. Chem. Informationsdienst 1978, 9 ( (49 ), ).10.1002/chin.197849031.
Little J. L. ; Friesen G. D. ; Todd L. J. Preparation and properties of selenaboranes and telluraboranes. Inorg. Chem. 1977, 16 (4 ), 869–872. 10.1021/ic50170a030.
Keller W. ; Hofmann M. ; Wadepohl H. ; Enders M. ; Fanfrlík J. ; Hnyk D. Chlorinated polyhedral selenaboranes revisited by joint experimental/computational efforts: the formation of closo-1-SeB9Cl9 and the crystal structure of closo-SeB11Cl11. Dalton Trans. 2023, 52 , 16886–16893. 10.1039/D3DT02987E.37916993
Rao C. E. ; Yuvaraj K. ; Ghosh S. Diruthenium analogues of Hexaborane(12) and Pentaborane(9): Synthesis and structural characterization of [(1,2-Cp*Ru)2B2H6S2] and [(2,3-Cp*Ru)2B3H6(μ-η1-EPh)], (E = S, Se and Te) (Cp* = η5-C5Me5). J. Organomet. Chem. 2015, 776 , 123–128. 10.1016/j.jorganchem.2014.10.049.
Gao P. ; Wang X. ; Huang Z. ; Yu H. 11B NMR Chemical Shift Predictions via Density Functional Theory and Gauge-Including Atomic Orbital Approach: Applications to Structural Elucidations of Boron-Containing Molecules. ACS Omega 2019, 4 (7 ), 12385–12392. 10.1021/acsomega.9b01566.31460356
Bühl M. ; Thiel W. ; Fleischer U. ; Kutzelnigg W. Ab Initio Computation of 77Se NMR Chemical Shifts with the IGLO-SCF, the GIAO-SCF, and the GIAO-MP2Methods. J. Phys. Chem. 1995, 99 , 4000–4007. 10.1021/j100012a021.
Bayse C. A. Considerations for Reliable Calculation of 77Se Chemical Shifts. J. Chem. Theory Comput. 2005, 1 (6 ), 1119–1127. 10.1021/ct050136t.26631655
Rusakov Y. Y. ; Rusakova I. L. ; Krivdin L. B. MP2 calculation of 77Se NMR chemical shifts taking into account relativistic corrections. Magn. Reson. Chem. 2015, 53 (7 ), 485–492. 10.1002/mrc.4226.25998325
Duddeck H. Selenium-77 nuclear magnetic resonance spectroscopy. Prog. Nucl. Magn. Reson. Spectrosc. 1995, 27 (1–3 ), 1–323. 10.1016/0079-6565(94)00005-F.
Duddeck H. Annual Reports on NMR Spectroscopy; Academic Press, 2004; Vol. 52 , pp 105–166.10.1016/S0066-4103(04)52003-3.
Jelínek T. ; Cisařová I. ; Štíbr B. ; Kennedy J. D. ; Thornton-Pett M. Macropolyhedral boron-containing cluster chemistry. The [S2B18H19]− anion, and the reversible dismantling and regeneration of an apical boron cluster site with cluster connectivity six. J. Chem. Soc., Dalton Trans. 1998, (18 ), 2965–2968. 10.1039/a805791e.
Ormsby D. L. ; Greatrex R. ; Kennedy J. D. Macropolyhedral boron-containing cluster chemistry. The reversible disassembly and reassembly of the hexagonal pyramidal {B7} feature in the [S2B18H19]− anion. Dalton Trans. 2008, 12 , 1625–1634. 10.1039/b715915c.
Londesborough M. G. S. ; Macías R. ; Kennedy J. D. ; Clegg W. ; Bould J. Macropolyhedral Nickelaboranes from the Metal-Assisted Fusion of KB9H14. Inorg. Chem. 2019, 58 (19 ), 13258–13267. 10.1021/acs.inorgchem.9b02116.31497952
Hnyk D. ; Wann D. A. ; Holub J. ; Bühl M. ; Robertson H. E. ; Rankin D. W. H. The gas-phase structure of 1-Selena-closo-dodecaborane(11), 1-SeB11H11, determined by the concerted use of electron diffraction and computational methods. Dalton Trans. 2008, (1 ), 96–100. 10.1039/B714457A.18399235
Kaur P. ; Holub J. ; Rath N. P. ; Bould J. ; Barton L. ; Štíbr B. ; Kennedy J. D. Macropolyhedral boron-containing cluster chemistry. Nineteen-vertex [S2B17H17(SMe2)]. An unusual apical boron atom of cluster connectivity six that introduces a new polyhedral borane building block. Chem. Commun. 1996, (2 ), 273–275. 10.1039/CC9960000273.
Hofmann M. ; Goll S. K. Macropolyhedral thiaboranes with unusual arachno subclusters—a computational investigation. J. Organomet. Chem. 2002, 657 (1–2 ), 273–278. 10.1016/S0022-328X(01)01491-7.
Bicerano J. ; Marynick D. S. ; Lipscomb W. N. Molecular orbital studies on large closo boron hydrides. Inorg. Chem. 1978, 17 (12 ), 3443–3453. 10.1021/ic50190a028.
Roy D. K. ; Bose S. K. ; Anju R. S. ; Mondal B. ; Ramkumar V. ; Ghosh S. Boron Beyond the Icosahedral Barrier: A 16-Vertex Metallaborane. Angew. Chem., Int. Ed. Engl. 2013, 52 (11 ), 3222–3226. 10.1002/anie.201208849.23382039
Heřmánek S. Boron-11 NMR spectra of boranes, main-group heteroboranes, and substituted derivatives. Factors influencing chemical shifts of skeletal atoms. Chem. Rev. 1992, 92 (2 ), 325–362. 10.1021/cr00010a007.
Oldfield J. E. The Two Faces of Selenium. J. Nutr. 1987, 117 (12 ), 2002–2008. 10.1093/jn/117.12.2002.3320287
Frisch M. J. ; Trucks G. W. ; Schlegel H. B. ; Scuseria G. E. ; Robb M. A. ; Cheeseman J. R. ; Scalmani G. ; Barone V. ; Petersson G. A. ; Nakatsuji H. ; Li X. ; Caricato M. ; Marenich A. V. ; Bloino J. ; Janesko B. G. ; Gomperts R. ; Mennucci B. ; Hratchian H. P. ; Ortiz J. V. ; Izmaylov A. F. ; Sonnenberg J. L. ; Williams-Young D. ; Ding F. ; Lipparini F. ; Egidi F. ; Goings J. ; Peng B. ; Petrone A. ; Henderson T. ; Ranasinghe D. ; Zakrzewski V. G. ; Gao J. ; Rega N. ; Zheng G. ; Liang W. ; Hada M. ; Ehara M. ; Toyota K. ; Fukuda R. ; Hasegawa J. ; Ishida M. ; Nakajima T. ; Honda Y. ; Kitao O. ; Nakai H. ; Vreven T. ; Throssell K. J. A. ; Montgomery J. ; Peralta J. E. ; Ogliaro F. ; Bearpark M. J. ; Heyd J. J. ; Brothers E. N. ; Kudin K. N. ; Staroverov V. N. ; Keith T. A. ; Kobayashi R. ; Normand J. ; Raghavachari K. ; Rendell A. P. ; Burant J. C. ; Iyengar S. S. ; Tomasi J. ; Cossi M. ; Millam J. M. ; Klene M. ; Adamo C. ; Cammi R. ; Ochterski J. W. ; Martin R. L. ; Morokuma K. ; Farkas O. ; Foresman J. B. ; Fox D. J. Gaussian 16. Revision C.01: Wallingford CT, 2016 .
Pritchard B. P. ; Altarawy D. ; Didier B. ; Gibson T. D. ; Windus T. L. New Basis Set Exchange: An Open, Up-to-Date Resource for the Molecular Sciences Community. J. Chem. Inf. Model. 2019, 59 (11 ), 4814–4820. 10.1021/acs.jcim.9b00725.31600445
