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Article

Unraveling the Synthesis of SbCl(C3N6H4): A Metal-Melaminate Obtained through Deprotonation of Melamine with Antimony(III)Chloride

by
Elaheh Bayat
,
Markus Ströbele
and
Hans-Jürgen Meyer
*
Section for Solid State and Theoretical Inorganic Chemistry, Institute of Inorganic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
*
Author to whom correspondence should be addressed.
Chemistry 2023, 5(2), 1465-1476; https://doi.org/10.3390/chemistry5020099
Submission received: 4 May 2023 / Revised: 12 June 2023 / Accepted: 14 June 2023 / Published: 20 June 2023
(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Abstract

:
The discovery of melamine by Justus von Liebig was fundamental for the development of several fields of chemistry. The vast majority of compounds with melamine or melamine derivatives appear as adducts. Herein, we focus on the development of novel compounds containing anionic melamine species, namely the melaminates. For this purpose, we analyze the reaction of SbCl3 with melamine by differential scanning calorimetry (DSC). The whole study includes the synthesis and characterization of three antimony compounds that are obtained during the deprotonation process of melamine to melaminate with the reaction sequence from SbCl4(C9N18H19) (1) via (SbCl4(C6N12H13))2 (2) to SbCl(C3N6H4) (3). Compounds are characterized by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), and infrared spectroscopy (IR). The results give an insight into the mechanism of deprotonation of melamine, with the replacement of one, two, or eventually three hydrogen atoms from the three amino groups of melamine. The structure of (3) suggests that metal melaminates are likely to form supramolecular structures or metal-organic frameworks (MOFs).

Graphical Abstract

1. Introduction

In the 19th century, the foundation of amine-substituted s-triazine derivatives was laid for the first time by Liebig and Gmelin [1,2,3] with the synthesis of melamine, melam, melem and their condensation product called melon. Melamine (1,3,5-triazine-2,4,6-triamine) is the simplest and most intensively studied C/N/H compound synthesized from potassium thiocyanate and ammonium chloride for the first time (1834) by Liebig [1,4]. However, it can also be easily achieved with trimerization of cyanamide (CN2H2), while today, industrial productions take place from urea in tons [5,6,7]. Melamine has a relatively high-melting point for an organic compound and undergoes condensation reactions on heating. The condensation products melem, melam, and melon (Figure 1) of this ancestry compound have been studied extensively using various spectroscopy techniques [8,9]. For a long period, thermal condensation was not fully understood due to the chemical inertness and low solubility of these products [10]. In 1959, May conducted a study on the pyrolysis of melamine at temperatures between 200 °C and 500 °C [11]. Afterward, this process was investigated by several scientists, particularly by Schnick and Lotsch [12,13]. The temperature-programmed XRD (TPXRD) was used in the temperature range between 25 °C and 660 °C to clarify the exact temperatures of formation of condensed products, which shows that the sublimation temperature of melamine is approximately 360–370 °C at atmospheric pressure. However, TPXRD in semi-closed systems shows that the X-ray reflections of melamine disappear at 296 °C, and then melamine forms melam and melem, which are stable up to 379 °C [13]. Pure melem, which consists of internally hydrogen-bonded heptazine molecules, can be obtained at 379 °C and is stable up to 500 °C. The polymeric carbon nitride material melon is also achieved with further heating [13].
In addition to the many applications melamine has, such as surface coating [14], flame redundancy [14,15,16,17], and heavy metal removal [18,19], it has some unique characteristics which make it a relevant research topic up to this day. The most important potential of melamine is its ability to create a metal-organic framework (MOF) [20] or porous-organic framework (POFs) [21] by the formation of metal melaminates.
Justus von Liebig’s discovery of melamine was essential in the progress of C/N/H chemistry. Most melamine-containing compounds and their derivatives are found as adducts. Cationic C/N/H ions are present in various molecular compounds, including melamine, melam, and melem. These ions are formed by protonating the ring nitrogen atoms, which are more basic than the terminal amino groups. The most common cations are monoprotonated, but di- or trications have also been observed. More research into the chemistry of these substances led to the discovery of melaminium [22,23,24,25,26], melamium, and melemium salts. By far, the majority of salts were produced by melamine, including melaminium sulfate [27], melaminium nitrate, melaminium phosphates [16,28], melaminium chloride [29], organic slats of phthalates [30], benzoates, or citrates [31], and many inorganic salts containing complex anions [32,33]. On the other hand, a small number of melamium salts have been studied, such as melamium bromide and iodide [26]. Recently, melemium salts, namely melemium sulfate, triple protonated melemium methylsulfonate, and melemium perchlorate, are also discovered [34,35]. Melamine was also reported to coordinate with metal halides to form organic-inorganic hybrid copper halides such as Cu2Br2(C3N6H7)]n, [Cu3Cl3(C3N6H7)]n [36], the silver complex [Ag(C3N6H6)(H2O)(NO3)]n, and the mercury compound (C3N6H7)(C3N6H6)HgCl3 [37], which have biochemical applications and nonlinear optical properties [38,39].
Regarding the basic property of melamine, protonation is easy, and a great variety of such compounds, either theoretically or experimentally, have been investigated [25,26,40,41]. A new class of chemistry related to melaminates (deprotonated melamine) has received less attention until now; however, it is very important from either a chemistry or application perspective. The coordination behavior of molecules such as guanidine or melamine, capable of forming extended hydrogen bonds, can be changed by deprotonation [36,42]. Thus, it is a promising strategy for synthesizing interconnected supramolecular structures or MOFs. Despite the challenge which arises from the rigidity of its heterocyclic structure, the affinity of ring-N atoms to act as H-bond acceptors, and the steric hindrance of neighboring amino groups [35], the deprotonation of melamine seems to be plausible since guanidine (a stronger base) has already been deprotonated twice [43]. Franklin pioneered the work on anionic melaminate by synthesizing two compounds of K(C3N6H5)·NH3 and K3(C3N6H3) [44,45] in liquid ammonia. However, these compounds were only characterized using elemental analyses, and no crystallographic structure information was provided. Later, Dronskowski and coworkers confirmed the presence of the two ammonia adducts, K(C3N6H5)·NH3 and Rb(C3N6H5)·½NH3 by single-crystal X-ray diffraction. Ammonia-free K3(C3N6H3) has been assigned by its characteristic infrared bands, being compared with calculated bands from density-functional theory (DFT) [42]. There was no further research reported on these classes of compounds and their properties until the discovery and identification of the copper melaminate Cu3(C3N6H3) with a layered framework structure by Meyer & coworkers [20].
In this work, the step-wise deprotonation of melamine in a solid state has been studied by thermal analysis. Herein, antimony (III) chloride is used for the deprotonation of melamine due to its low melting point of 73.4 °C [46]. The recorded reaction sequence shows three compounds that were prepared and later characterized by powder X-ray diffraction (PXRD), single-crystal diffraction, and IR measurements. The structure of SbCl(C3N6H4) suggests the potential of synthesizing interconnected supramolecular structures or metal-organic frameworks (MOFs).

2. Materials and Methods

2.1. Materials

The starting materials, melamine (2,4,6-triamino-1,3,5-triazine, purchased from Sigma-Aldrich, 99%), and antimony(III)chloride (Sigma-Aldrich, 99%), ammonium chloride (Sigma-Aldrich, 99.99%) were used without further purification. The reaction mixtures were prepared under an argon atmosphere in a glovebox with moisture and oxygen levels below 1 ppm and transferred into homemade silica tubing (inner diameter 13 mm and 7 mm) and sealed under vacuum. The reactions were carried out in Simon–Müller and Carbolite chamber furnaces.

2.1.1. Synthesis

  • Synthesis of SbCl4(C9N18H19) (1):
Precursors were pestled in an agate mortar with a 1:4 molar ratio of antimony(III)chloride and melamine. A mixture of antimony(III) chloride and melamine with a total mass of ≈200.0 mg was transferred into a homemade silica ampule and sealed therein under vacuum. The ampoule was placed into a Simon–Müller furnace and heated to 200 °C for 20 h with a heating rate of 2 °C/min and cooling ramp of 0.5 °C/min (Figure S1). The reaction produced a white color product crystallized on the top of the ampule (>90% yield w.r.t Sb). A temperature gradient seemed to play an essential role in the separation of the product (1).
The solubility of compound (1) has been investigated in acetonitrile, THF, DCM, ethanol, methanol, and water. The PXRD measurements showed the decomposition of this product to unknown phases.
  • Synthesis of (SbCl4(C6N12H13))2 (2):
Similar to the previous preparation, the mixture of antimony (III)chloride and melamine was mixed in a 1:2 molar ratio (total mass of ≈200.0 mg) and heated to 200 °C for 20 h with a heating and cooling rate of 2 °C/min (Figure S1). The product was X-ray amorphous powder and contained transparent single crystals of (2) (10% w.r.t Sb).
  • Synthesis of SbCl(C3N6H4) (3):
The structure of (3) was obtained from both (1:2 and 1:4) ratios of antimony(III)chloride and melamine by heating the 1:2 ratio at 250 °C for 20 h, or by heating the 1:4 ratio at 280 °C for 20 h (Figure S1). The beige color product was isolated in 50% yield w.r.t Sb.
The solubility of compound (3) has been studied in many solvents. The powder was soaked for one hour in acetonitrile, THF, DMF, DCM, ethanol, methanol, water, and diluted acetic acid. Subsequent PXRD measurements were undertaken. The results showed that compound (3) remains stable in acetonitrile, THF, DMF, DCM, ethanol, and methanol. However, in water and DMSO, compound (3) decomposes and forms Sb2O3 and an unknown phase, respectively. The schematic synthesis of all three compounds is presented in Figure S1.

2.1.2. X-ray Powder Diffraction

The X-ray diffraction of prepared powders was recorded with a powder diffractometer (STOE Darmstadt, STADIP, Ge-monochromator) using Cu-Kα1 (λ = 1.540598 Å) radiation in the range of 5 < 2θ < 120°. Match3! Software [47] was used to compare the patterns with patterns of the corresponding crystal structures.

2.1.3. Single-Crystal X-ray Diffraction

Single Crystals of (1), (2), and (3) were selected and placed on a single-crystal X-ray diffractometer (Rigaku XtaLab Synergy-S) with Cu-Kα radiation (λ = 1.54184 Å) and a mirror monochromator at 150 or 220 K. Crystal structures were solved by direct methods (SHELXT) [48], followed by full-matrix least-squares structure refinements (SHELXL-2014) [49]. The absorption correction of X-ray intensities was performed with numerical methods using the CrysAlisPro 1.171.41.92a software (Rigaku Oxford Diffraction). Hydrogen atoms were found in the difference map and refined therefrom isotropically.

2.1.4. Thermoanalytic Studies

Differential scanning calorimetry (DSC) was carried out using a DSC 204 F1 Phoenix (Fa. Netzsch, Selb, Germany). The starting materials were enclosed under Ar in a glovebox into gold-plated (5 μm) steel autoclaves with a volume of 100 μL (Bächler Feintech AG in Hölstein, Switzerland). The reactions of SbCl3 with melamine were analyzed for different ratios between room temperature and 500 °C at a heating and cooling rate of 2 °C/min.

2.1.5. Infrared Spectra

The infrared (IR) spectra of samples were recorded with a Bruker VERTEX 70 FT-IR spectrometer within the spectra range of 400−4000 cm−1. Tablets of KBr were used as a background.

3. Results and Discussion

3.1. Thermoanalytic Studies

Thermal analyses based on DSC and DTA have been shown to be highly insightful regarding the examination of reaction sequences [50,51] and for comprehensive studies of binary or ternary systems [52], especially when combined with PXRD studies. Following this method, the formation or decomposition of a crystalline species is usually indicated by a thermal event, and the newly formed species is characterized by X-ray diffraction techniques.
The differential scanning calorimetric (DSC) measurements of 1:2 and 1:4 molar mixtures of antimony chloride and melamine are shown in Figure 2, with heating and cooling rates of 2 °C/min. The DSC patterns display a small exothermic peak at around 70 °C, which can be attributed to the melting point of antimony(III)chloride. Figure 2a,b show multiple exothermic effects between 200 °C and 300 °C. The resolution of thermal events in this region is rather poor and cannot be significantly improved by changing the heating ramp. For example, we have explored different heating rates throughout. At lower heating rates, the signals were smeared out and were not as sharp as the signals shown in Figure 2a,b, so the resolution was worse. The presented heating rate is the optimized heating rate with respect to the signal-to-noise ratio. Moreover, the effects are slightly different for different ratios of starting materials, with lower reaction temperatures in the presence of more melamine.
Powder XRD patterns were recorded on samples obtained under conditions given in the DSC experiments, being interrupted at certain temperatures, especially in the temperature region between 200 °C and 280 °C. Compound (1) was already formed at 200 °C from a 1:4 ratio of starting materials, and compound (2) was observed in the XRD pattern from a 1:2 ratio at the same temperature. Compound (3) was identified at around 280 °C from a 1:4 ratio of starting materials or, alternatively, at 250 °C from a 1:2 ratio. The endothermic peaks at 370 °C indicate the melting/decomposition of (excess) melamine, which appears sharper for the 1:4 ratio due to the larger amount of melamine. This assignment is confirmed by a DSC of melamine (Figure S2), which shows a similar endothermic peak with a slight shift at 361 °C. At slightly higher temperatures, compound (3) is decomposed, which is followed by a strong exothermic peak at 400 °C and 417 °C for the 1:4 and a 1:2 ratio, respectively. These intense exothermic peaks led to the formation of a phase with a yellow color (4) that looked glassy under the microscope. This was further studied by means of IR spectroscopy (see the relevant section).
From this study, we note that reactions in the given system proceed very quickly, almost simultaneously, making the assignment of compounds and their preparations challenging. This is due to the high reactivity of reaction partners.

3.2. Crystal Structures

Crystal structures of all three compounds (1), (2), and (3) were solved and refined based on single-crystal X-ray diffraction data with triclinic (P 1 − ) and monoclinic (P21/c and P21/n) space groups, respectively, with crystallographic details summarized in Table 1 and relevant distances given in Table 2. The asymmetric unit of each compound is shown in Figure S3.
The crystal structure of (1) is composed of one deprotonated melamine, two protonated melamine and a single chloride ion besides SbCl3 to make up SbCl4(C3N6H5)(C3N6H7)2. The crystal structure contains a sequence of three distinct layers stacked on top of each other (along b); one of them is displayed in Figure 3. Stacking behavior is most common for melamine-based structures.
The SbCl3 entity in the structure, with its lone pair, is well known from several crystal structures having average Sb-Cl distances of 260.1 pm [53]. The antimony is connected with an exocyclic nitrogen atom of the melaminate ion (C3H5N6)− via Sb-N4 (204.7(3) pm) and an obviously weaker interaction via Sb-N1 (253.6(3) pm). The constituents in each layer in (1) are interconnected by a network of hydrogen bonds (Figure 3a). An isolated Cl− ion in the structure is interconnected by hydrogen bridges at dH-Cl = 216.3 pm and 225.6 pm, consistent with the corresponding value in melaminium chloride dH-Cl = 239.7 pm [29].
The crystal structure of (2) comprises one deprotonated melamine, three protonated melaminium ions, an SbCl3 unit and an (SbCl5)2− ion to make up (SbCl4)2(C3N6H5)(C3N6H7)3 displayed in Figure 4. The average Sb-Cl distances in SbCl3 are 259.3 pm, and those of SbCl5 are 262.1 pm and 257.8 pm, supporting the presence of Sb3+ throughout. Antimony in SbCl3 is interconnected with the melaminate ion (C3H5N6)− via Sb-N4 (204.4(6) pm) and an obviously weaker interaction via Sb-N1 (256.1(3) pm). Again, the crystal structure features a layered arrangement and hydrogen bridging within layers.
The crystal structure of (3) features the presence of (SbCl)2+ and the melaminate ion (C3N6H4)2− in SbCl(C3N6H4). Unlike the two previous systems, this structure can be described as an infinite chain structure due to the bridging connectivity of the divalent melaminate anion, all shown in Figure 5. The (SbCl)2+ (dSb-Cl = 254.9(3) pm) is interconnected via exocyclic nitrogen atoms of two melaminate ions via Sb-N4 (204.4(6) pm) and Sb-N6 (208.6(8) pm) interactions and an obviously weaker interaction via Sb-N2 (241.5(1) pm).
The stacking sequences of layers are often dominated by the preference that the N atom of the triazine ring in one layer is alternating with a C atom of the triazine ring in the next layer, which is a characteristic feature in copper melaminate [20] and metal cyanurates as well [54,55]. This is achieved by rotating or shifting C3N3 units in adjacent layers relative to each other. However, this is not apparent in the structure of compounds (1–3). Layered arrangements of C3N3 units are quite clearly visible in compounds (1) and (2) but not in compound (3) (Figures S3–S6). Hence there is the possibility of π-π interactions between C3N3 units in (1) and (2). Such interactions can play a crucial role in the stabilization of parallel and antiparallel ring architectures in the crystal structure. The centroid-to-centroid distance at which C3N3 rings may be considered representative of π-π stacking interactions is 360–390 pm in compounds (1) and (2). This distance increases to 560–590 pm in (3) which might present no π-π interactions between layers in this structure.
The range from 357–393 pm was previously reported for several compounds [38,56,57]; for example, in a zinc(II) complex containing melamine (392.8 pm) [56]. In many other studies of copper halide complexes (357.2–389.2 pm), we can see the stacking behavior of twisted melamine rings, which represents the π-π interactions [58].

3.3. X-ray Powder Diffraction and Infrared Spectroscopy

The reaction products were investigated by PXRD, and the XRD patterns of (1), and (3) are provided in Figures S7 and S8. Therein, the recorded data are compared with the calculated patterns obtained from the structure refinement based on single-crystal data. Compound (2) was obtained in low yield; therefore, no powder pattern of this intermediate could be recorded. This compound was always found in the presence of (3) or melamine at higher and lower temperatures, respectively. The powder pattern of compound (3) in Figure S8 shows some unidentified diffraction peaks.

3.4. Infrared Spectroscopy (IR)

The IR spectrum of (1), (3) and (4) has been compared to that of melamine and melaminium chloride, as presented in Figure 6. Table S1 lists the frequencies associated with each vibrational mode of these molecules, along with the corresponding bond assignments. Three IR absorption bands, indicative of the asymmetric and symmetric stretching of -NH2 groups of melamine, can be found in the 3500–3300 cm−1 range of the melamine spectrum [29,59]. These vibrations can overlap with the -NH+ in melaminium chloride, and due to coupling, the peak is broadened [60]. The characteristic bands of -NH2 groups and -NH+ are also seen in the spectrum of compound (1) at 3462, 3357, and 3433 cm−1. We can see that the first peak (3462 cm−1) in compound (1) is shifted to lower wavenumbers when compared to melamine. This shift may be due to the presence of protonated melamine units in (1). In fact, the presence of hydrogen bonding would shift -NH2 IR bands to lower wavenumbers, as the hydrogen bond would weaken the NH2 bond and lower its vibrational frequency [61]. However, due to coupling with the N-H…Cl stretching mode or the presence of heavier atoms (Cl, Sb) in compound (1), the second peak (3357 cm−1) is shifted to slightly higher wavenumbers and also broadened [29]. Similarly, infrared spectra for compounds (3) and (4) indicate that the asymmetric and symmetric vibrations of -NH2 overlap with those of -NH+ in both compounds, as evidenced by the disappearance of the first peak (3471 cm−1 for melamine) and the broadening of the other two peaks. The bending mode bands for melaminium chloride and compound (1) are substantially higher than those for melamine (1652 cm−1) at 1722, 1676, 1649 cm−1 and 1679, 1656, and 1612 cm−1, respectively. This is explained by the fact that melaminium chloride and (1) have fewer intermolecular interactions than melamine. In compounds (3) and (4), bending modes are split into multiple bands, showing that -NH2 groups in these compounds have different vibrational frequencies due to the presence of neighboring atoms and molecular interactions in these structures. The region below 1500 cm−1 is related to C-N, and C=N ring stretching modes, C-N side group stretching, N-H rocking, and triazine ring breath and bending vibrations, which are listed with detailed numbers in Table S1. The exact position of these peaks can depend on various factors, such as the substitution pattern of the triazine ring and the nature of the surrounding chemical environment, which agrees well with the slight shifts in each region for compounds (1), (3), and (4). The strong split-band at 800 cm−1, which is brought on by the sextant-bend of both the triazine and heptazine rings, provides additional evidence that compound (4) is still either a heptazine- or triazine-based compound (IR cannot differentiate between triazine and heptazine) [13,22,62], whereas the yellow emission color of the compound under ultraviolet radiation rather indicates a heptazine based compound.

4. Conclusions

The development of metal melaminates is just at its beginning. A preparative concept for the development of melaminates was recently established for Cu3(C3H3N3) based on the reaction of CuCl with melamine. The same concept is employed in this study for the reaction of SbCl3 with melamine. Thermal studies (DSC) reveal a narrow sequence of thermal events, or rather intertwining reactions that reveal new compounds, following the sequence (1), (2) and (3) with increasing temperature.
Indeed, the final product of the given reaction cascade is compound (3), observed via compounds (1) and (2). For a better description of the reaction sequence of compounds, we use the abbreviation Mel for melamine, with Mel(n−) for melaminate and Mel(+) for melaminium. The overall reaction representing the formation of compound (3) can be described as follows:
SbCl3 + Mel → SbClMel(2−) + 2 HCl↑
The formation of HCl in this reaction can be equivalent to melaminium chloride (Mel(+)Cl), which is, in fact, present in compound (1) but is lost at elevated temperatures through sublimation, which indeed has been reported as a side-phase for the corresponding reaction of CuCl and melamine [20]. This reaction scheme with metal halide and melamine is indeed a useful way to develop metal melaminates. However, reactions with melamine are intrinsically difficult due to the high reactivity and condensation behavior of melamine.
The reaction of SbCl3 with excess melamine passes through some intermediate reaction stages with the formations of melamine derivatives (Mel−, Mel+) that are successively lost with increasing temperature from (1) to (2) and finally (3). Compound (1) is best described as SbCl4Mel(−)(Mel(+))2 containing three melamine species per antimony atom, and compound (2) is given as (SbCl4)2Mel(−)(Mel(+))3 and contains only two melamine derivatives per antimony atom until only one melaminate is left in (3). The formation of the expectable compound SbMel(3−) is not observed.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/chemistry5020099/s1, Reference [29] is also cited in the supplementary materials.

Author Contributions

Conceptualization, supervision, funding acquisition, review and editing, H.-J.M.; Synthesis, PXRD and IR, writing, E.B.; X-ray diffraction refinements and structure solutions, M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data is contained within the article and Supplementary Materials.

Acknowledgments

A sincere thank you to Mike Healey Smith for his diligent English revisions and proofreading of this article.

Conflicts of Interest

The authors declare no conflict of interest.

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Chemistry 05 00099 g001 550
Figure 1. Molecular structures of melamine (C3N6H6), melam (C6N11H9) and melem (C6N10H6).
Figure 1. Molecular structures of melamine (C3N6H6), melam (C6N11H9) and melem (C6N10H6).
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Chemistry 05 00099 g002 550
Figure 2. (a) DSC of the reaction of SbCl3 and melamine in a ratio of 1:4, (b) DTA of the reaction of SbCl3 and melamine in a ratio of 1:2.
Figure 2. (a) DSC of the reaction of SbCl3 and melamine in a ratio of 1:4, (b) DTA of the reaction of SbCl3 and melamine in a ratio of 1:2.
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Figure 3. (a) Constituents of one layer in the structure of (1) as SbCl4(C3N6H5)(C3N6H7)2, and (b) a perspective view of the unit cell of (1) along the b-axis, with the color code: N: blue, C: gray, H: white, Cl: green, Sb: red).
Figure 3. (a) Constituents of one layer in the structure of (1) as SbCl4(C3N6H5)(C3N6H7)2, and (b) a perspective view of the unit cell of (1) along the b-axis, with the color code: N: blue, C: gray, H: white, Cl: green, Sb: red).
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Figure 4. (a) Section of the crystal structure of (2) as (SbCl4)2(C3N6H5)(C3N6H7)3 projected on the bc-plane, and (b) a perspective view along the b-axis with the color code: N: blue, C: gray, H: white, Cl: green, Sb: red).
Figure 4. (a) Section of the crystal structure of (2) as (SbCl4)2(C3N6H5)(C3N6H7)3 projected on the bc-plane, and (b) a perspective view along the b-axis with the color code: N: blue, C: gray, H: white, Cl: green, Sb: red).
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Figure 5. (a) Section of a chain section of the crystal structure of (3) and (b) a perspective view of the unit cell roughly along the a-axis with the color code: N: blue, C: gray, H: white, Cl: green, Sb: red.
Figure 5. (a) Section of a chain section of the crystal structure of (3) and (b) a perspective view of the unit cell roughly along the a-axis with the color code: N: blue, C: gray, H: white, Cl: green, Sb: red.
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Figure 6. FTIR spectrum of melamine, melaminium chloride powder, compared with compounds (1), (3), (4).
Figure 6. FTIR spectrum of melamine, melaminium chloride powder, compared with compounds (1), (3), (4).
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Table
Table 1. Crystallographic details of the crystal structure refinement of compounds (1), (2), and (3).
Table 1. Crystallographic details of the crystal structure refinement of compounds (1), (2), and (3).
Compound(1)(2)(3)
CCDC code220127322102442213381
Formula weight642.971033.67281.32
Temperature/K220.0(1)150.0(1)150.0(1)
Wavelength/Å1.541841.541841.54184
Space groupP 1 − P21/cP21/n
a/Å9.5878(5)13.2780(2)5.3562(2)
b/Å10.5395(3)10.6878(1)10.5432(3)
c/Å11.4338(5)24.0953(2)12.5618(4)
α/°74.011(3)9090
β/°79.122(4)105.860(1)93.710(3)
γ/°85.602(3)9090
Volume/Å31090.37(8)3289.26(7)707.90(4)
Z244
Rint0.03640.04850.0312
Goodness-of-fit on F21.0741.0441.044
wR2 (all data)0.06600.06070.0267
wR20.06430.06030.0264
Final R indices
(all data)		0.03390.02510.0120
R10.02780.02430.0110
ϴMax./°4.3653.4605.483
ϴMin./°66.58566.58370.067
μ/mm−114.9319.47833.932
ΔρMax./e·Å−30.5082.4910.322
ΔρMin./e·Å−3−0.593−0.597−0.451
Completeness/%97.310099.8
Table
Table 2. Selected interatomic distances (pm) of compounds (1), (2), and (3).
Table 2. Selected interatomic distances (pm) of compounds (1), (2), and (3).
Compound (1)Compound (2)Compound (3)
AtomAtomLength/pmAtomAtomLength/pmAtomAtomLength/pm
Sb1Cl1276.5(8)Sb1Cl3284.7(6)Sb1N2241.5(1)
Sb1N1253.6(3)Sb1Cl4260.6(0)Sb1N6208.6(8)
Sb1Cl2247.0(0)Sb1Cl5248.7(2)Sb1N4204.4(6)
Sb1Cl3256.8(2)Sb1Cl1240.2(1)Sb1Cl1254.9(3)
Sb1N4204.7(3)Sb2N1256.1(3)
Sb2N4204.7(3)
Sb2Cl6279.2(7)
Sb2Cl7247.2(8)
Sb2Cl8251.1(1)
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Bayat, E.; Ströbele, M.; Meyer, H.-J. Unraveling the Synthesis of SbCl(C3N6H4): A Metal-Melaminate Obtained through Deprotonation of Melamine with Antimony(III)Chloride. Chemistry 2023, 5, 1465-1476. https://doi.org/10.3390/chemistry5020099

AMA Style

Bayat E, Ströbele M, Meyer H-J. Unraveling the Synthesis of SbCl(C3N6H4): A Metal-Melaminate Obtained through Deprotonation of Melamine with Antimony(III)Chloride. Chemistry. 2023; 5(2):1465-1476. https://doi.org/10.3390/chemistry5020099

Chicago/Turabian Style

Bayat, Elaheh, Markus Ströbele, and Hans-Jürgen Meyer. 2023. "Unraveling the Synthesis of SbCl(C3N6H4): A Metal-Melaminate Obtained through Deprotonation of Melamine with Antimony(III)Chloride" Chemistry 5, no. 2: 1465-1476. https://doi.org/10.3390/chemistry5020099

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