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Short Note

N,N,N′-Tris(trimethylsilyl)-2-pyridinecarboximidamide

by
Mukaila A. Ibrahim
1,
Kathryn E. Preuss
1 and
René T. Boeré
2,*
1
Department of Chemistry, University of Guelph, Guelph, ON N1G 2W1, Canada
2
Department of Chemistry and Biochemistry and The Canadian Centre for Advanced Fluorine Technologies, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
*
Author to whom correspondence should be addressed.
Molbank 2025, 2025(3), M2031; https://doi.org/10.3390/M2031
Submission received: 1 June 2025 / Revised: 19 June 2025 / Accepted: 24 June 2025 / Published: 3 July 2025
(This article belongs to the Section Structure Determination)
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Abstract

N,N,N′-tris(trimethylsilyl)-carboximidamides are effective reagents in synthetic chemistry in reactions with both non-metal and metal halides, because the side product is the mild and volatile ClSi(CH3)3 rather than corrosive HCl. The title compound inserts the 2-pyridylamidinate fragment into several non-metal systems, including custom chelating radical ligands. The single-crystal X-ray diffraction structure was determined and modeled by Hirshfeld atom refinement using custom aspherical atomic scattering factors. Excellent data quality led to a model with enhanced precision of all interatomic distances and free refinement of H-atom positions and anisotropic displacement ellipsoids. This structure model is compared to the four previously published analogous structures.

1. Introduction

N,N,N′-tris(trimethylsilyl)-carboximidamides, commonly known as persilylamidines or trisilylamidines (always with trimethylsilyl groups) [1,2], are niche reagents for the introduction of RCN2 moieties into a variety of unsaturated element molecules [3,4,5,6], including primary amidines [1] and especially for the preparation of element-N,N′-amidinates, [7,8]. The title compound 1 (Figure 1) has been used by some of us for the synthesis of 4-(2-pyridyl)-1,2-dithia-3,5-diazolyl [3], a custom stable π-radical ligand that coordinates to a variety of metals to form complexes with single molecule magnetic properties [9,10,11,12,13]. Such persilylamidines are ideal reagents towards main group element chlorides because the byproducts of reaction are trimethylsilyl chloride, benign and volatile neutral molecules that afford much better control than typical reactions of NH reagents that release highly acidic non-aqueous HCl [3,4,5,6,7,8]. For example, 1 reacts with excess sulfur monochloride via a disproportionation reaction to afford the dithiadiazolium chloride in hot acetonitrile as an orange crystalline solid in high purity and in excellent yield. Under these conditions, the ClSi(CH3)3 byproduct is benign (Scheme 1).
Despite their high utility and close to 300 structurally characterized element-amidinate derivatives, there is a paucity of structural studies on persilylamidines. The Cambridge Structure Database (CSC, Release 2024.3.1) [14] records just four such structures, 2–5 (Figure 1). Herein we report a high accuracy single-crystal X-ray diffraction (SC-XRD) structure determination of 1, measured at 100 K, and its Hirshfeld atom refinement (HAR) using custom aspherical form factors [15] that allows for the placement and full refinement of all atoms including hydrogen. This approach is significant because 1 is a dense element-organic structures whose outer surface is almost entirely defined by a rind of hydrogen atoms. The structural features of 1 are compared to those of 2–5, the first detailed structural comparison ever undertaken for persilylamidines.
Molbank 2025 m2031 g001
Figure 1. Line structures of all persilylamidines for which 3D geometries from SC-XRD are known. CSD refcodes: 2 VAJSOO [16], 3 PEWJEH [17], 4 POXYEG [18], 5 SARSIN [19] (TMS = Si(CH3)3).
Figure 1. Line structures of all persilylamidines for which 3D geometries from SC-XRD are known. CSD refcodes: 2 VAJSOO [16], 3 PEWJEH [17], 4 POXYEG [18], 5 SARSIN [19] (TMS = Si(CH3)3).
Molbank 2025 m2031 g001

2. Results and Discussion

2.1. Preparation, Identification and SC-XRD Structure Model

The title compound, 1 was prepared by a modification of the original report [3] and characterized by comparing the 1H and 13C NMR spectra with the literature. Clear, colorless crystals formed by spontaneous crystallization of the distilled yellow-green oil within 24 h at room temperature (21 °C). The single-crystal X-ray diffraction (SC-XRD) structure was obtained at low temperature (100 K) from a very high-quality dataset (see Materials and Methods section for details). The structure refinement with the ‘independent atom model’ (IAM) was optimized further with an efficient procedure for HAR employing high-speed DFT methods to calculate custom aspherical atomic scattering factors [15]. This approach was successful for placing the H-atoms at near-neutron accuracy, allowed full anisotropic displacement ellipsoids for all the H-atoms and led to an average precision for the most common bonds in the structure, i.e., d(C–C) = 0.0015 Å, that is 35% lower than possible with the IAM in a closely parallel standard refinement [20]. Such an overall structure precision improvement fits with the high data quality (relevant indicators: Rint = 0.0230, I/σ(I) = 70.2, final R1 = 0.0204, wR2 = 0.0457), as we have previously reported [20].

2.2. Molecular Structure Description of 1 as Found in Crystals

The title compound 1 crystallizes in space group P21/n, the most common space group for racemic organic and metal–organic compounds because this enables the highest density of packing (Dcalc = 1.075 g/cm3), but with Z′ = 2. This means that two different conformations share the asymmetric unit that is repeated by the lattice symmetry elements ( 1 ¯ -centers, n-glides and 21-screw axes). These are depicted in Figure 2a,b and will be called the C1 and C16 conformers. The two adopted conformations in the crystal lattice differ by subtle variations concerning the rotations of the Si(CH3)3 methyl groups as well as that of the 2-pyridyl ring with respect to the respective central C atoms. An analysis of the void spaces finds four spheres per unit cell together accounting for 42 Å3, corresponding to 1% of the total volume, and far too small to accommodate any solvent, consistent with the spontaneous crystallization of the vacuum-distilled oil.
The metric parameters of the two conformers are contrasted in Table 1, which shows that the chemical structures of the two conformers are identical and metric parameters are quite similar. A statistical comparison of bond distances shows that the C1-C2, N1-Si1 and N2-Si2 lengths in the C1 conformer cannot be considered the same at the 99% confidence level to equivalents in the C16 conformer. C1-C2 is longer than C16-C17, whilst N1-Si1 < N4-Si4 and N2-Si2 < N5-Si5. No obvious geometrical reason could be found for this discrepancy in local molecular or lattice structures; however, it should be recognized that the standard uncertainties of refinement (s.u.) are very small, which amplifies the differences.
The central amidine moieties (i.e., C2C1N1N2, etc.) are effectively planar (mean deviation = 0.002 ± 0.003) Å; ∑∠ = 359.82 ± 13 & 359.80 ± 12°). There is a distinct difference between the formal C–N single and C=N double bonds in both molecules (ΔCN = 0.119 ± 0.010 Å) despite that the trisubstituted N2 & N5 environments are also very close to planar (mean deviation = 0.10 Å; ∑∠ = 358.92(9) & 358.62(9)°) [21]. The 2-pyridyl rings (which are strongly planar, σ(0.012) Å for each) are twisted from this central CCN2 plane by 51.86(5) and 54.67(5)° into the same relative orientations, i.e., that in which N3/N6 make their closest approaches to N1/N4.
To further validate the HAR model, we have analyzed the statistics of the H-atom positional refinement. There are two different kinds of E–H bonds. For the pyridine C(aromatic)–H, the average over 8 exemplars is uniform at 1.099 ± 0.010 Å, but noticeably longer than 1.079 ± 0.003 Å from a previous comparison of 17 structures, albeit of considerably variable quality, reported by us [22]. A reference point is available from neutron diffraction data, using a critical review of the literature for experiments at 60 ≤ T ≤ 140 K [23] of 1.085 ± 0.009 Å. Interestingly, both sets of NoSpherA2 results are indistinguishable from the neutron data at the 99% confidence level, though they are from each other. For the SiMe3 C(sp3)−H bonds the average over a more statistically meaningful 53 exemplars is 1.084 ± 0.016 Å, which may be compared to 1.090 ± 0.022 Å in 90 exemplars of this bond type [22]. It is, of course, possible to both restrain and constrain E–H bonds within the HAR method, but at this emergent stage of the use of NoSpherA2, we prefer to report unconstrained refinements wherever these have good statistics and do not deviate far from chemical expectations. In the future, as standards develop in the community, restrained refinements of longish bonds as found here for the aryl C–H bonds may become recommended practice [20]. Satisfyingly, the behavior of the large number of independent silyl group C–H in the model developed here for the structure of 1 is found to be reliable with good statistics.

2.3. Molecular Structure of 1 Compared to the Literature

A geometric comparison was also undertaken between the geometry found for 1 with the four previous structures of persilylated amidines 2–5 (column 4 of Table 1) [16,17,18,19]. Here, the averages include the values for the two independent geometries in 1 and the std dev is over all compounds (six structures), for the central (tristrimethylsiyl)amidine core.
Noticeably, for all these central moiety bond lengths, the values in 1 average about 0.005 Å longer than the comparators, despite that these were all collected at higher temperature than 1 (153–295, vs. 100 K) given the general expectations that bonds contract slightly on cooling. The planarity of the central amidine moieties (i.e., C2C1N1N2, etc.) over the comparison set is strongly conserved (∑∠mean = 359.82 ± 0.09°). The ΔCN value for the series ranges between 0.118 and 0.144 Å, whereby this value is smallest in both molecules of 1 in this set. In all these compounds, ∠C=N–Si for the formal imino group is large at 136.4 ± 2.2°, variable, and with larger values trending weakly with increased ΔCN.
Also of note is that the three N–Si bonds are distinct over the whole set of five compounds, with d(N1-Si1) < d(N2-Si3) < d(N2-Si2), consistently. If we now compare to the CSD average values, it is found that for ((CH3)3Si)2N–E bonds, where E is any non-metal, the average Si–N length is 1.76 ± 2 Å over 1181 exemplars, while for (CH3)3Si–N=C bonds, the average is 1.72 ± 3 Å for 99 exemplars. For the three different types of N–Si bonds, we see that in all cases for 1–5, the values in these persilylated amidine lengths are longer than the respective CSD means, with the average d(N2-Si2) at 1.780 ± 0.007 Å deviating most from the 1.76 ± 2 Å CSD mean, and on average over the two molecules in 1 of 1.7900 ± 0.0010) Å in the far upper quartile for bonds of this type. All these comparisons are indicative of considerable steric pressure on the Si(CH3)3 groups in persilylated amidines. This finding fits well with the long reaction times and high reaction temperatures required especially in the insertion of the ‘last’ silyl group into the molecules [1,2]. Indeed, structures are known for the Ar-C(NSi(CH3)3)2Li, the expected synthetic intermediates, in which the two silyl substituents correspond directly to Si1 and Si3 in the structures of 1–5 [24,25].

2.4. Lattice Structure of 1

A depiction of the lattice structure of 1 is provided in a unit cell diagram (Figure 3). Important intermolecular contacts, including non-classical C–H∙∙∙N hydrogen bonds are reported in Table 2. There is a chain of H-bonds that links the pyridyl N3/N6 atoms to the pyridyl C19/4–H atoms, that is, to the C para to the N in each ring. Thereby, the two distinct molecules are linked to each other in an infinite C 2 2 ( 12 ) chain (in Etter notation) [26]. Given the high symmetry displayed in the other known persilylamidine SC-XRD structures (all of which are either Z′ = 1 or Z′ = ½), it may be speculated that the Z′ = 2 packing adopted in 1 represents a compromise between the very uniform molecular structures induced by the high steric pressure at the amidine centers and the adoption of this H-bonded chain. Of course, these are non-classical H-bonds, but especially the d(H∙∙∙A) of ~2.4 Å and ∠D–H∙∙∙A of ~161° place them near the upper limit of “weak” H-bonds in the classification of Jeffrey [27]. Additional, weaker, dispersive interactions are found linking between H-bonded chains of molecules, forming double contacts (pyridyl) H20∙∙∙H9C (Si(CH3)3) and (Si(CH3)3) H30A ∙∙∙H8C (Si(CH3)3).
By contrast, for the other known persilylamidine structures 2–5, there are no intermolecular contacts <∑rvdW in 2 (refcodes: VAJSOO) [16], 4 (POYXEG) [18], 5 (SARSIN) [19]. In 3 (PEWJEH), there are very marginal contacts between Si(CH3)3 H atoms [17]; however, it needs to be remembered that as IAM refinements, the C–H bonds in these comparators are intrinsically shorter than in the HAR structure of 1.

3. Discussion

Persilylated amidines are extremely useful reagents, especially with element chlorides of the main group. The byproducts of reaction are thereby altered from the often-destructive HCl to innocuous and easily separated ClSi(CH3)3. They show good reactivity albeit less than the most common alternate reagents, the corresponding bistrimethylsilyl lithium amidinates. Despite this apparent advantage for the latter, there are numerous results that show the entrainment of Li+ in the coordination spheres of products [28,29,30]. When this is not desirable, consideration should be given to employing the available persilylamidines. These molecules are reliably synthesized for a large range of amidines (via the corresponding nitriles) and can be effectively purified by vacuum distillation.
This report has highlighted the highly conserved structures of (aryl) persilylamidines and has pointed out the structural evidence for considerable steric pressure on the Si(CH3)3 groups. It is difficult to drive three Si(CH3)3 groups into the coordination environment of aryl amidines; indeed, this may be impossible for backbone substituents that are bulkier than flat aromatic rings [1,2]. Further structural investigations, experimental and computational, on this interesting class of reagents would be welcomed.

4. Materials and Methods

General Materials and Procedures

The reaction was performed under argon using a Schlenk line. Toluene, diethyl ether, and chlorotrimethylsilane (ClSi(CH3)3) were purchased from Sigma-Aldrich, while 2-pyridinecarbonitrile (PyCN) was obtained from TCI Chemicals, USA. Toluene was dried over sodium metal before use. Lithium bis(trimethylsilyl)amide diethyl ether adduct (LiN(Si(CH3)3)2·Et2O) was synthesized following a literature method [1]. Nuclear magnetic resonance (NMR) spectra (1H and 13C) were recorded at ambient temperature (22 °C) using a 300 MHz Bruker Avance II liquid-state spectrometer (Bruker, Germany). Spectra were referenced to the residual solvent peak (CHCl3 in the case of CDCl3: 7.26 ppm for 1H and 77.0 ppm for 13C). NMR coupling constants are reported in Hertz (Hz), using abbreviations such as d = doublet and br = broad. Chemical shifts are reported in parts per million (ppm).
Synthesis and characterization. 2-(2′-Pyridyl)-N,N,N′-tris(trimethylsilyl)amidine (compound 1) was prepared by modification of a literature method [3]. A solution of PyCN (2.00 g, 19.2 mmol) in 10 mL of toluene was added dropwise via a dropping funnel to a suspension of LiN(Si(CH3)3)2·Et2O (4.64 g, 19.2 mmol) in 20 mL of toluene. The mixture was stirred for 2 h at 40 °C. ClSi(CH3)3 (2.47 mL, 19.5 mmol) was then added dropwise using a syringe, and the resulting slurry was refluxed for 12 h. The reaction mixture was filtered warm under argon using a coarse glass filter stick, and the solvent was removed under reduced pressure to afford a dark residue. Compound 1 was purified by distillation as a yellowish-green oil at 80 °C under 10−2 mbar, yielding 4.17 g (64.3%). 1H NMR (300 MHz, CDCl3): δ 8.54 (d of d of d, JHH = 4.8 Hz, JHH = 2.2 Hz, JHH = 0.72 Hz pyridylmeta, 1H); δ 7.62 (d of d of d, JHH = 14.1 Hz, JHH = 7.9 Hz, JHH = 1.8 Hz, pyridylmeta, 1H); δ 7.28 (d, JHH = 7.8 Hz, pyridylortho, 1H); δ 7.20 (d of d of d, JHH = 12.4 Hz, JHH = 4.8 Hz, JHH = 1.2 Hz pyridylpara, 1H); δ 0.0415 (br s, Si(CH3)3, 27H). 13C-{1H} NMR (300 MHz, CDCl3): δ 166.5 (s, amidineipso C), δ 159.2 (s, pyridylipso C), δ 149.1 (s, pyri-dymeta), δ 136.1 (pyridylpara C), δ 123.7 (s, pyridylmeta C), δ 123.0 (s, pyridylortho C), δ 2.7 (s, Si(CH3)3 C).
SC-XRD. Single crystals of 1 (C15H31N3Si3) were obtained as colorless blocks from the crystallization of the distilled yellowish-green oil within 24 h at room temperature (21 °C). A suitable crystal was selected under a microscope, placed on a 100 μm MiTeGen crystal mount using Paratone™ oil (caution: the crystals tend to dissolve in Paratone, so rapid freezing is necessary) and cooled directly on the goniometer using the Oxford Cryostream 800 cooling system of a Dual source Cu/Mo SuperNova diffractometer equipped with a Pilatus 200K HPC detector. The crystal was kept at 100(1) K during data collection. Using Olex2 [31], the structure was solved with the SHELXT [32] structure solution program using Intrinsic Phasing and refined with the olex2.refine [33] refinement package using Gauss-Newton minimization. After full refinement within the Independent Atom Method (IAM), the model was tested for stability towards Hirshfeld atom refinement using custom aspherical atomic scattering factors. The software environment of NoSpherA2, an implementation of NOn-SPHERical Atom-form-factors in Olex2 [15], was employed. The ED is calculated from a Gaussian basis set single determinant SCF wavefunction with DFT using selected functionals, for a fragment of the crystal. This fragment can be embedded in an electrostatic crystal field by employing cluster charges. The following options were used: ORCA 5.0 [34], partitioning with NoSpherA2 [15], normal integration accuracy, R2SCAN/def2-TZVP level of theory with a charge of 0 and a spin multiplicity of 1. The refinement was continued to full convergence of both the scattering factors and atomic positions.
Crystal Data for C15H31N3Si3 (M =337.690 g/mol): monoclinic, space group P21/n (No. 14), a = 10.3530(1) Å, b = 35.8670(4) Å, c = 12.1771(2) Å, β = 112.633(2)°, V = 4173.51(11) Å3, Z = 8, Z′ = 2, T = 100.15 K, μ(Cu Kα) = 2.070 mm−1, Dcalc = 1.075 g/cm3, 41,440 reflections measured (4.92° ≤ 2Θ ≤ 151.06°), 8491 unique (Rint = 0.0230, Rsigma = 0.0142) which were used in all calculations. The final R1 was 0.0204 (I ≥ 2σ (I)) and wR2 was 0.0457 (all data). CCDC 2453762.

Supplementary Materials

Detailed crystal structure report; archival 1H and 13C NMR spectra. Figure S1: Displacement ellipsoids plot (20% probability) depicting the asymmetric unit in the structure of 1 (Z’ = 2); Table S1: Crystal data and structure refinement for 1; Table S2: Fractional Atomic Coordinates (×104) and Equivalent Isotropic Displacement Parameters (Å2×103) for 1. Ueq is defined as 1/3 of the trace of the orthogonalised UIJ tensor; Table S3: Anisotropic Displacement Parameters (Å2×103) for 1. The Anisotropic displacement factor exponent takes the form: -2π2[h2a*2U11+2hka*b*U12+…]; Table S4: Bond Lengths for 1; Table S5: Bond Angles for 1; Table S6: Non-Classical Hydrogen Bonds for 1; Table S7: Torsion Angles for 1; Table S8: Hydrogen Atom Coordinates (Å×104) and Isotropic Displacement Parameters (Å2×103) for 1; Figure S2: 1H NMR Spectrum of 1 (300 MHz, CDCl3 solution, referenced to the CHCl3 residual); Figure S3: 13C NMR Spectrum of 1 (75 MHz, CDCl3 solution, referenced to the CDCl3 signal).

Author Contributions

Conceptualization, R.T.B. and K.E.P.; investigation, M.A.I.; resources, R.T.B.; data curation, R.T.B.; writing—original draft preparation, R.T.B.; writing—review and editing, K.E.P.; supervision, K.E.P.; funding acquisition, K.E.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Natural Sciences and Engineering Research Council (NSERC) of Canada Discovery Grant (DG; grant No. RGPIN-2020-03969) to K.P. R.B. acknowledges career research support from the NSERC through the Discovery Grants program. The diffractometer at the University of Lethbridge X-ray Diffraction Facility was purchased by the University and the Faculty of Arts & Science.

Data Availability Statement

Data available for this work is provided in the Supporting Information (detailed report of the SC-XRD diffraction study; archival NMR spectra). Raw SC-XRD data has been deposited via the joint CCDC/FIZ Karlsruhe deposition service and can be accessed by citing the data acquisition code 2453762.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
DcalcCalculated density from SC-XRD
DFTXDensity functional theory
HARHirshfeld Atom Refinement
NMRNuclear Magnetic Resonance
NoSpherA2NOn-SPHERical Atom-form-factors in Olex2
PyDTDA4-(2-pyridyl)-1,2-dithia-3,5-diazolyl
SC-XRDSingle-Crystal X-ray Diffraction
s.u.standard uncertainty from least squares refinement

Appendix A

Previously published SC-XRD structures have been reported for four other compounds as mentioned in Section 2.3 and Figure 1. Each comparator is also an aromatic persilylamidine, so that there are six common bond types between 2–3 and the two independent molecules found in the unit cells of 1. The data used to compute the average values listed in Table 1 are provided explicitly in Table A1. The much smaller s.u. achieved for 1 compared to 2–5 is very apparent.
Table A1. Comparison of the common C–C{NSiMe3}N(SiMe3)2 bond distances in 1–5 1.
Table A1. Comparison of the common C–C{NSiMe3}N(SiMe3)2 bond distances in 1–5 1.
Parameter1 (C1)1 (C16)2345Average
C1-N11.2777(11)1.2774(11)1.268(3)1.279(7)1.270(7)1.270(3)1.274 ± 0.004
C1-N21.3958(11)1.3978(10)1.411(3)1.403(5)1.414(7)1.413(3)1.406 ± 0.007
C1-C21.5068(11)1.5033(11)1.497(2)1.503(6)1.505(7)1.507(4)1.504 ± 0.003
N1-Si11.7362(8)1.7340(7)1.722(2)1.729(4)1.715(4)1.724(2)1.727 ± 0.007
N2-Si21.7881(7)1.7911(7)1.775(2)1.770(4)1.777(5)1.777(2)1.780 ± 0.007
N2-Si31.7746(7)1.7730(7)1.766(2)1.774(4)1.762(4)1.766(3)1.769 ± 0.005
N2-C1-N1120.89(8)120.71(7)119.6(2)119.8(4)120.2(5)120.4(2)120.3 ± 0.5
C2-C1-N1121.77(8)121.35(7)123.5(2)123.6(4)124.5(5)123.5(2)123.0 ± 1.1
C2-C1-N2117.16(7)117.75(7)116.6(2)116.6(4)115.1(4)115.9(2)116.5 ± 0.9
C1-N1-Si1132.65(6)134.69(7)136.6(2)136.6(3)138.7(4)139.0(2)136.4 ± 2.2
C1-N2-Si2112.69(5)111.72(6)111.9(1)113.1(3)112.2(4)113.3(2)112.5 ± 0.6
C1-N2-Si3123.88(6)124.10(6)123.1(1)122.1(3)121.7(4)121.4(2)122.7 ± 1.0
Si2-N2-Si3122.35(4)122.80(4)124.5(1)123.1(2)125.0(3)124.2(1)123.7 ± 1.0
∠(arom/amid) 251.8654.6756.1348.0848.7351.4051.4 ± 3.1
1 Columns 2,3 constitute the two independent molecules in 1. CSD refcodes for 2: VAJSOO; 3: PEWJEH; 4: POYYEG; 5: SARSIN). 2 ∠(arom/amid) is the torsional angle between the planes of the aromatic rings and of the CCN2 moieties of the persilylamidines.

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Molbank 2025 m2031 sch001
Scheme 1. A typical example of the synthetic utility of persilylamidines such as 1 in reactions with element chlorides, yielding 4-(2′-pyridyl)-1,2-dithia-3,5-diazolium chloride (pure, 94%) [3].
Scheme 1. A typical example of the synthetic utility of persilylamidines such as 1 in reactions with element chlorides, yielding 4-(2′-pyridyl)-1,2-dithia-3,5-diazolium chloride (pure, 94%) [3].
Molbank 2025 m2031 sch001
Molbank 2025 m2031 g002
Figure 2. Displacement ellipsoids plots (40% probability) of the two independent molecules of 1 as found in the crystal lattice with H-atoms omitted and showing the atom numbering scheme. (a) Molecule C1; (b) Molecule C16.
Figure 2. Displacement ellipsoids plots (40% probability) of the two independent molecules of 1 as found in the crystal lattice with H-atoms omitted and showing the atom numbering scheme. (a) Molecule C1; (b) Molecule C16.
Molbank 2025 m2031 g002
Molbank 2025 m2031 g003
Figure 3. Displacement ellipsoids (20%) plot of a unit cell packing diagram of the structure of 1 also showing shortest intermolecular contacts that are rvdW–0.2 Å (red contact lines are somewhat shorter than those that are purple). The view is down the ac bisector with b horizontal.
Figure 3. Displacement ellipsoids (20%) plot of a unit cell packing diagram of the structure of 1 also showing shortest intermolecular contacts that are rvdW–0.2 Å (red contact lines are somewhat shorter than those that are purple). The view is down the ac bisector with b horizontal.
Molbank 2025 m2031 g003
Table 1. Selected intermolecular distances (Å) and angles (°) of the C1 and C16 molecules found in the crystalline state from the SC-XRD structure of 1 and average values for 2–5 1,2.
Table 1. Selected intermolecular distances (Å) and angles (°) of the C1 and C16 molecules found in the crystalline state from the SC-XRD structure of 1 and average values for 2–5 1,2.
ParameterMolecule C1Molecule C16Av. Compar. 2
C1-N11.2777(11)1.2774(11)1.274 ± 0.004
C1-N21.3958(11)1.3978(10)1.406 ± 0.007
C1-C21.5068(11)1.5033(11)1.504 ± 0.003
N1-Si11.7362(8)1.7340(7)1.727 ± 0.007
N2-Si21.7881(7)1.7911(7)1.780 ± 0.007
N2-Si31.7746(7)1.7730(7)1.769 ± 0.005
C2-N31.3408(11)1.3409(11)n.a.
C2-C31.3957(12)1.3955(12)n.a.
C3-C41.3919(14)1.3920(13)n.a.
C4-C51.3933(16)1.3923(14)n.a.
C5-C61.3929(15)1.3918(14)n.a.
C6-N31.3388(12)1.3368(11)n.a.
N2-C1-N1120.89(8)120.71(7)120.3 ± 0.5
C2-C1-N1121.77(8)121.34(7)123.0 ± 1.1
C2-C1-N2117.16(7)117.75(7)116.5 ± 0.9
C1-N1-Si1132.65(6)134.69(6)136.4 ± 2.2
C1-N2-Si2112.69(5)111.72(6)112.5 ± 0.6
C1-N2-Si3123.88(6)124.10(6)122.7 ± 1.0
Si2-N2-Si3122.35(4)122.80(4)123.7 ± 1.0
∠(arom/amid) 351.86(5)54.67(5)51.4 ± 3.1
1 To facilitate comparison, the parameters are listed for the respective atoms in the C1 molecule, cf. Figure 2a, and equivalent values for the C16 conformer are provided in the third column. 2 Averages with std dev over the structures of 1–5 (CSD refcodes: VAJSOO, PEWJEH, POYYEG, SARSIN); full data are compiled in Appendix A. 3 ∠(arom/amid) is the torsional angle between the planes of the aromatic rings and of the CCN2 moieties of the persilylamidines.
Table 2. Shortest intermolecular contacts as found in the crystal lattice of 1.
Table 2. Shortest intermolecular contacts as found in the crystal lattice of 1.
DHAd(D–H)/Åd(H∙∙∙A)/Åd(D∙∙∙A)/ÅD–H∙∙∙A/°
C4H4N61.110(12)2.390(12)3.4649(13)162.4(10)
C19H19N3 11.089(12)2.435(12)3.4840(13)161.2(10)
H9C H20 2 2.165(18) 154.8(14)
H8C H30A 2 2.180(20) 132.9(13)
1 +x, +y, −1 + z; 2 −1/2 + x, 1/2 − y, 1/2 + z.
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Ibrahim, M.A.; Preuss, K.E.; Boeré, R.T. N,N,N′-Tris(trimethylsilyl)-2-pyridinecarboximidamide. Molbank 2025, 2025, M2031. https://doi.org/10.3390/M2031

AMA Style

Ibrahim MA, Preuss KE, Boeré RT. N,N,N′-Tris(trimethylsilyl)-2-pyridinecarboximidamide. Molbank. 2025; 2025(3):M2031. https://doi.org/10.3390/M2031

Chicago/Turabian Style

Ibrahim, Mukaila A., Kathryn E. Preuss, and René T. Boeré. 2025. "N,N,N′-Tris(trimethylsilyl)-2-pyridinecarboximidamide" Molbank 2025, no. 3: M2031. https://doi.org/10.3390/M2031

APA Style

Ibrahim, M. A., Preuss, K. E., & Boeré, R. T. (2025). N,N,N′-Tris(trimethylsilyl)-2-pyridinecarboximidamide. Molbank, 2025(3), M2031. https://doi.org/10.3390/M2031

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