Bioinorganic Chemistry and Applications
Volume 2021 (2021), Article ID 6638229, 10 pages
https://doi.org/10.1155/2021/6638229

Research Article

Preparation and Thermogravimetric and Antimicrobial Investigation of Cd (II) and Sn (II) Adducts of Mercaptopyridine, Amino Triazole Derivatives, and Mercaptothiazoline Organic Ligand Moieties

Ahmed Gaber,¹ Walaa F. Alsanie,² Robson F. de Farias,³ and Moamen S. Refat⁴

¹Department of Biology, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia
²Department of Clinical Laboratories Sciences, The Faculty of Applied Medical Sciences, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia
³Departamento de Química, Universidade Federal de Roraima, Cx. Postal 167, Boa Vista 69301-970, Roraima, Brazil
⁴Department of Chemistry, Faculty of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia

Correspondence should be addressed to Moamen S. Refat; msrefat@yahoo.com

Received 9 December 2020; Revised 27 February 2021; Accepted 2 April 2021; Published 16 April 2021

Academic Editor: Guillermo Mendoza-Diaz

Copyright © 2021 Ahmed Gaber et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The solid adducts of SnCl₂.(3amt).H₂O, SnCl₂.2(3amt).H₂O, CdCl₂.(3amt), CdCl₂.2(3amt), SnCl₂.(2mct).0.5H₂O, SnCl2.2(2mct), CdCl₂.(2mct), CdCl₂.2(2mct).H₂O, SnCl₂.(2mcp).1.5H₂O, >₂.2(2mcp).4H₂O, CdCl₂.(2mcp), CdCl₂.2(2mcp), SnCl₂.(4amt).4H₂O, SnCl₂.2(4amt).1.5H₂O, CdCl₂.(4amt).H₂O, and CdCl₂.2(4amt) (where the 3amt, 4amt, 2mct, and 2mcp represent 3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole, 2-mercaptothiazoline, and 2-mercaptopyridine simple organic chelates, respectively) were prepared using a solid-state route and investigated by CHN elemental analysis and infrared spectroscopy. Additionally, we investigated the thermogravimetric characterization and antimicrobial proprieties. It is verified that for 3amt and 4amt adducts, the coordination occurs through nitrogen atom. For 2mct compounds, the coordination occurs through nitrogen (Sn) or sulfur (Cd). For 2mcp adducts, both coordination sites nitrogen and sulfur are involved. By examination of TG curves, it is confirmed that for each hydrated compounds, the first mass loss step is linked with the release of water molecules followed by the release of ligand molecules and sublimation of the metal chloride. Furthermore, it is verified that, considering only the release of ligand molecules (3amp, 4amp, 2mct, or 2mcp), the cadmium adducts are always more stable than the correspondent tin adducts probably due to the formation of cross-linking bonds in these compounds. Finally, of these 16 adducts, 14 showed antimicrobial activities against different bacterial and fungal strains.

1. Introduction

In the past decades, the problem of multidrug-resistant microorganisms has reached an alarming level worldwide, and the synthesis of new antimicrobial compounds has become an urgent need to treat microbial infections. Organic compounds that include heterocyclic ring systems continue to attract significant interest due to their wide range of biological elements [1]. The nucleus 1,2,4-triazole is incorporated into a variety of important therapeutic agents, which mainly exhibit antimicrobial activities [1, 2]. Among the various five-membered heterocyclic systems, 1,2,4-triazoles and 1,3,4-thiadiazoles and their derivatives gain importance because they constitute the structural features of many bioactive compounds [2]. Triazole and thiadiazole rings are known to be included in the structure of various drugs [3, 4]. From these classes of heterocyclic compounds, the synthesis of novel derivatives of 1,2,4-triazole-3-thionate and 2-amino-1,3,4-thiazole has attracted great interest due to various biological properties such as antibacterial [5, 6], antifungal [7], antituberculosis [8, 9], interferon [10], antioxidant [11], antitumor [12], anti-inflammatory [13, 14], and anticonvulsant [15].

The thermogravimetry analysis technique is employed to identify the acceptability level regarding the coordination nature in between the central metal ions and different kinds of interesting biomolecule chelates, such as amino acids [16], caffeine molecule [17], or chemical materials that have a biological behavior as ethylene- and propylene-urea as well as ethylene-thiourea [18]. Moreover, the thermogravimetric information shows very close relationships with the calorimetric data [19] and the spectral data [20].

The main goal of this article is to investigate the synthesis, thermal analyses, and antimicrobial data of the sixteen solid adducts for the Cd (II) and Sn (II) metal ions coordinated with the 3amt, 4amt, 2mct, or 2mcp organic molecules. The molecular structural formulas of 3amt, 4amt, 2mct, and 2mcp are displayed in Figure 1. The sixteen solid adducts are SnCl₂.(3amt).H₂O, SnCl₂.2(3amt).H₂O, CdCl₂.(3amt), CdCl₂.2(3amt), SnCl₂.(2mct).0.5H₂O, SnCl2.2(2mct), CdCl₂.(2mct), CdCl₂.2(2mct).H₂O, SnCl₂.(2mcp).1.5H₂O, SnCl₂.2(2mcp).4H₂O, CdCl₂.(2mcp), CdCl₂. 2(2mcp), SnCl₂.(4amt).4H₂O, SnCl₂.2(4amt).1.5H₂O, CdCl₂.(4amt).H₂O, and CdCl₂.2(4amt).

Figure 1: The structural forms of 3amt, 4amt, 2mct, and 2mcp.

2. Materials and Methods

All used reagents were purchased from Sigma-Aldrich and were utilized with no additional purification.

All solid Cd(II) and Sn(II) adducts were prepared by the solid-state pathway by grinding stoichiometric amounts of metal halides and organic moieties (3amt, 4amt, 2mct, and 2mcp) in a mortar for 70 minutes at room temperature (27°C). The prepared solid adducts were dried under vacuum at room temperature for 24 h. This solid-state pathway was successfully used to enhance coordination reactions [21–24] as an alternative to conventional synthesis in solution. The synthesis is performed at room temperature, and where no solvent is used, any unwanted reaction to the metal cation is avoided. The infrared spectra result considering both free organic ligands and sixteen solid adducts proved that there are no free ligand particles after the grinding process.

C, H, and N elemental analysis were performed using a Perkin-Elmer 2400 analyzer. Infrared spectra of the solid adducts as a powder in situ KBr discs were scanned using a Gengis II FTIR apparatus within the 4000–400 cm⁻¹ range, with a resolution of 4 cm⁻¹. Thermogravimetric diagrams under N₂ atmosphere were analyzed on the Shimadzu TG-50H apparatus with a heating rate of 15°C min⁻¹.

Tin(II) and cadmium(II) contents were determined by gravimetry by the direct ignition of the adducts at 600°C for 3 h till constant weight. The residue was then weighted in the forms of SnO and CdO, respectively. The Mohr method uses chromate ions as an indicator in the titration of chloride ions with a silver nitrate standard solution. After all the chloride precipitated as white silver chloride, the first excess of titrant results in the formation of a silver chromate precipitate, which signals the end point.

Preparation of standard AgNO₃ solution: 9.0 g of AgNO₃ was weighed out, transferred to a 500 mL volumetric flask, and made up to volume with distilled water. The resulting solution was approximately 0.1 M. This solution was standardized against NaCl. Reagent-grade NaCl was dried overnight and cooled to room temperature. 0.25 g portions of NaCl were weighed into Erlenmeyer flasks and dissolved in about 100 mL of distilled water. In order to adjust the pH of the solutions, small quantities of NaHCO₃ were added until effervescence ceased. About 2 mL of K₂CrO₄ was added, and the solution was titrated to the first permanent appearance of red Ag₂CrO₄.

The antimicrobial activity of all adducts were performed as previously explained in detail by Gaber et al. [21]. Escherichia coli and Pseudomonas aeruginosa were used as Gram-negative bacteria, whereas Bacillus subtilis and Staphylococcus aureus were used as Gram-positive bacteria. In addition, Aspergillus flavus and Candida albicans were used as fungal strains. Diameters of the inhibition zones around the hole were calculated [21].

3. Results and Discussion

Table 1 shows the data of the elemental analysis. These results are like the proposed formulas. Additionally, the main infrared bands are displayed in Tables 2–5. Before a discussion on the infrared data, it is important to note that considering (3amt and 4amt) and (2mct and 2mcp), organic molecules have a rich electron donor sites through the lone pair of electrons presented on the nitrogen and sulfur atoms, respectively. Moreover, for the four chelates, there is more than one potential coordination site, which makes them able, at the very first moment, to act as cross-links.

Table 1: Mass weight and carbon, hydrogen, and nitrogen elemental analysis data for the examined compounds.

Adducts
M.wt
% C
% H
% N

Calc.
Found
Calc.
Found
Calc.
Found

SnCl₂.(3amt).H₂O
291.68
8.22
8.11
2.05
2.02
19.19
18.94

SnCl2.2(3amt).H₂O
375.76
12.77
12.25
2.66
2.61
29.81
29.44

CdCl2.(3amt)
267.37
8.97
8.89
1.49
1.45
20.94
20.73

CdCl₂.2(3amt)
351.47
13.65
13.62
2.27
2.20
31.87
31.48

SnCl₂.(2mct).0.5H₂O
317.81
11.33
10.99
1.89
1.84
4.40
4.35

SnCl₂.2(2mct)
428.02
16.82
16.32
2.33
2.28
6.54
6.43

CdCl₂.(2mct)
302.52
11.90
11.74
1.65
1.59
4.62
4.55

CdCl₂.2(2mct).H₂O
439.73
16.37
16.22
2.73
2.68
6.37
6.18

SnCl₂.(2mcp).1.5H₂O
327.77
18.31
18.19
2.44
2.41
4.27
4.15

SnCl₂.2(2mcp).4H₂O
483.94
24.80
24.57
3.72
3.68
5.78
5.74

CdCl₂.(2mcp)
294.48
20.37
20.22
1.69
1.68
4.75
4.72

CdCl₂.2(2mcp)
405.65
29.58
29.29
2.46
2.45
6.90
6.84

SnCl₂.(4amt).4H₂O
345.68
6.94
6.91
3.47
3.41
16.19
15.98

SnCl₂.2(4amt).1.5H₂O
384.76
12.48
12.34
2.86
2.79
29.11
28.96

CdCl₂.(4amt).H₂O
285.37
8.40
8.34
2.10
2.07
19.62
19.48

CdCl₂.2(4amt)
351.47
13.65
13.51
2.27
2.26
31.87
31.83

Table 2: Major infrared bands (cm⁻¹) for 3amt and its Cd(II) and Sn(II) adducts.

3amt
CdCl₂-(3amt)
CdCl₂-2(3amt)
SnCl₂-(3amt)
SnCl₂-2(3amt)
Assignments

3398 s
3419 ms
3340 ms
3312 w
3349 vw
(N-H); NH₂

3326 mw
3356 w

3310 vw

3316 mw

3258 vw

3182 mw
3213 w
3212 ms
3155 mw
3155 ms
(N-H); NH₂

3131 w
3153 vw

1647 vs
1652 vs
1645 w, sh
1688 vs
1677 vs
δb(NH₂)

1590 s
1573 w
1594 vs
1569 ms
1566 ms
ν(C=N)

1533 s
1537 s
1560 vs

ν(N=N)

1480 w
1479 vs

1418 s
1429 ms
1374 vs
1405 mw
1415 w
Ring breathing bands

1389 ms
1373 w

1339 ms
1326 s

1332 ms

1275 vs
1283 s
1248 vs
1257 ms
1263 w
ρr (NH₂)

1217 vs
1250 vw
1213 ms
1125 vw
1125 ms
ν(C-N)

1219 vs
1144 vs

1144 w

1045 vs
1088 w
1083 vs
1048 s
1066 s
ρw (NH₂)

945 vs
1057 s
1011 vs
951 vs
950 vs

991 s

873 vs
901 s
884 s
860 ms
867 s
ρt (NH₂)

830 s
740 ms
747 sh
748 w, sh
773 ms

729 vs
693 vw
726 ms

644 vs
694 vs

642 ms

s = strong; w = weak; m = medium; sh = shoulder; v = very; br = broad; ν = stretching; δ = bending.

Table 3: Major infrared bands (cm⁻¹) for 4amt and its Cd(II) and Sn(II) adducts.

4amt
CdCl₂-(4amt)
CdCl₂-2(4amt)
SnCl₂-(4amt)
SnCl₂-2(4amt)
Assignments

3312 w
3467 ms
3303 s
3417 w
3418 w, br
(N-H); NH₂

3368 ms
3258 vw
3317 ms
3277 w, br

3307 ms

3197 w
3199 s
3198 s
3127 ms
3129 w, br
(N-H); NH₂

3139 w
3136 s
3105 s

1647 vs
1618 vs
1618 vs
1623 vs
1685 w
δb(NH₂)

1533 s
1543 s
1537 s
1539 ms
1631 vs

1529 s

1475 ms
1474 mw
1470 w
1465 vw
1465 vw
Ring breathing bands

1404 s
1398 s
1394 w
1402 vw
1412 vw

1341 s
1346 w
1366 vw
1363 vw

1318 vw
1323 vw

1188 s
1209 s
1209 ms
1207 ms
1205 s
ρr (NH₂)

1074 s
1145 vw
1078 s
1164 vw
1075s
ν(C–N)

1082 vs

1135 vw

1075 s

1016 vw
1025 s
1015 s
1034 s
1033 s
ρw (NH₂)

959 ms
980 vs
984 ms
934 ms
935 ms

873 s
908 w
894 ms
871 ms
875 ms
ρt (NH₂)

672 w
874 s
845 vw
690 w, sh
661 ms

689 ms
686 ms

s = strong; w = weak; m = medium; sh = shoulder; v = very; br = broad; ν = stretching; δ = bending.

Table 4: Major infrared bands (cm⁻¹) for 2mct and its Cd(II) and Sn(II) adducts.

2mct
CdCl₂-(2mct)
CdCl₂-2(2mct)
SnCl₂-(2mct)
SnCl₂-2(2mct)
Assignments

2852 w
3258 s
3258 s
3443 s, br
3447 ms, br
(C-H); –CH₂

2948 vw
3136 ms
3206 ms
3207 w
(O-H); H₂O

2998 w
3144 vw
3136 w

2947 w
2997 w
2997 w

2844 w
2929 w
2848 vw

2845 w

2709 mw
—
—
—
—
ν(SH)

2565 mw

1518 vs
1515 vs
1515 vs
1539 vs
1539 w, sh
ν(C=N)

1514 s
Ring breathing bands

1260 w
1308 s
1305 s
1307 s
1294 s
(C-N)

1217 w
1250 vw
1249 w
1253 w
1250 vw
(C-N) + ν(C-C)

1160 w
1192 ms
1193 s
1208 w
1205 vw
ν(C-S); C – SH

1102 s
1142 w
1045 vs
1167 w
1041 s

1045 vs

1038 s

s = strong; w = weak; m = medium; sh = shoulder; v = very; br = broad; ν = stretching; δ = bending.

Table 5: Major infrared bands (cm⁻¹) for 2mcp and its Cd(II) and Sn(II) adducts.

2mcp
CdCl₂-(2mcp)
CdCl₂-2(2mcp)
SnCl₂-(2mcp)
SnCl₂-2(2mcp)
Assignments

—
3458 ms, br
3448 ms, br
3421 ms, br
3423 ms, br
ν(OH); H₂O

3196 ms
3172 ms
3216 ms
3073 vw

3126 ms

3135 w

3087 s

2709 mw
—
—
—
—
ν(SH)

2537 mw

1576 vs
1602 vs
1585 vs
1582 vs
1578 vs
Ring breathing bands

1504 s
1517 s
1513 s
1550 sh
1551 sh

1446 ms
1443 s
1443 s
1517 s
1438 vs

1418 s
1378 s
1370 s
1438 vs
1366 w

1360 s

1275 ms
1262 s
1252 s
1259 vs
1262 s
ν(C=N); aromatic

1246 ms
1160 ms
1163 s
1155 w, sh
1179 vw
δ(C-H); in-plane bend

1188 vs

1145 vs
1134 vs
1132 vs
1131 s
1136 s
ν(C-S); C – SH

1102 vw
1111 vw
1109 vw
1080 ms
1081 ms

s = strong; w = weak; m = medium; sh = shoulder; v = very; br = broad; ν = stretching; δ = bending.

In case of 3amt adducts, the overall decrease observed for the symmetrical and asymmetrical N-H bands suggests that the NH₂ group is engaged with the coordination. Furthermore, positive shifts observed for the δb bands reinforce this statement. It is worth noting that the observed shifts are more intense to Sn(II) adducts than to Cd(II), which is probably due to the higher acidity of Sn(II) (larger nuclear effective charge: 5.65 for Sn and 4.35 for Cd). It is verified that the symmetrical N-H bands are more sensitive to this acidity difference since a positive shift is observed for Cd(II) adducts, whereas a negative shift of this band is verified to Sn(II) adducts.

In case of 4amp approximation, the same general orientation is observed for asymmetric and symmetric N-H bands. This fact indicates that in this case, NH₂ is involved to a slight degree in the metallic coordination. This hypothesis is reinforced by the fact that for 4amp, the ringed breathing bands exhibit a negative shift (compared to free chelates and synthesized solid adducts), whereas positive shifts are observed in 3amp. Therefore, for 4amp adducts, the two “isolated” nitrogen atoms are the main coordination sites. Suggested coordination modes for 3amp and 4amp molecules are shown schematically in Figure 2.

(a)

(b)

Figure 2: Schematic representation of the suggested coordinative characteristics for (a) 3amt and (b) 4amt adducts.

As explicatory examples, the infrared spectra of 3amt solid adducts are shown in Figure 3.

Figure 3: Infrared spectra for (a) CdCl₂-(3amt), (b) CdCl₂-2(3amt), (c) SnCl₂-(3amt).H₂O, and (d) SnCl₂-2(3amt).H₂O.

In case of 2mct adducts, positive shifts of the νC = N band are observed for Sn(II) adducts, whereas negative shifts are verified to Cd(II) adducts. Such fact suggests a coordination through nitrogen to Sn(II) and a coordination through sulfur to Cd(II) in agreement with the fact that the nitrogen atom is a hard base and that Sn(II) is a harder acid than Cd(II).

For 2mcp adducts, the negative shifts observed for the ν(C-S); C-SH and ν(C=N) aromatic bands suggest that, in this case, both coordination sites N and S are involved in the coordination process for both cations considered.

The data of thermogravimetric curves for the 16 solid adducts are demonstrated in Figure 4. The main TG data are elucidated in Table 6.

Figure 4: Thermogravimetric curves for the 16 solid adducts.

Table 6: TG data summary for Sn(II) and Cd(II) adducts with 3amt, 4amt, 2mcp, and 2mcp.

Adduct
Step
ti (°C)
Degradation tf (°C)
Process onset (°C)
Mass loss (%)

SnCl₂.(3amt).H₂O
1
55
382
238
26.7

2
385
560
473
35.5

SnCl2.2(3amt).H₂O
1
45
102
76
5.1

2
160
445
320
40.0

3
447
606
517
27.2

CdCl2.(3amt)
1
280
331
307
53.7

2
332
406
348
12.8

3
478
660
569
29.3

CdCl₂.2(3amt)
1
188
271
234
24.1

2
348
448
401
16.8

3
449
681
587
43.0

SnCl₂.(2mct).0.5H₂O
1
31.4
83
50
3.3

2
127
344
237
43.2

3
346
461
404
7.5

4
462
615
513
6.2

SnCl₂.2(2mct)
1
120
260
204
44.0

2
261
341
288
10.2

3
342
430
378
4.7

4
431
595
513
8.9

5
596
656
607
1.1

CdCl₂.(2mct)
1
181
276
223
30.2

2
497
650
583
41.3

CdCl₂.2(2mct).H₂O
1
136
276
207
43.2

2
277
485
384
15.4

3
486
628
551
9.3

SnCl₂.(2mcp).1.5H₂O
1
110
199
154
8.0

2
200
355
285
55.4

3
421
654
534
3.1

SnCl₂.2(2mcp).4H₂O
1
103
221
154
14.3

2
222
349
302
82.1

3
584
670
585
1.8

CdCl₂.(2mcp)
1
186
309
244
23.3

2
310
459
391
12.6

3
460
647
576
47.0

4
648
751
675
8.6

CdCl₂.2(2mcp)
1
139
274
215
35.8

2
276
349
301
5.2

3
351
482
399
10.1

4
483
649
572
26.9

SnCl₂.(4amt).4H₂O
1
46
145
110
2.8

2
210
299
269
15.7

3
300
425
355
37.0

4
428
616
515
10.2

SnCl₂.2(4amt).1.5H₂O
1
63
191
133
6.8

2
192
319
257
39.2

3
320
407
358
18.2

4
497
619
545
14.2

CdCl₂.(4amt).H₂O
1
88
176
123
6.7

2
274
381
328
21.1

3
382
459
407
7.9

4
460
655
583
51.3

CdCl₂.2(4amt)
1
195
289
256
17.9

2
290
390
324
23.7

3
392
456
420
4.8

4
457
679
583
47.5

ti and tf are the initial and final temperatures of the thermal degradation process, respectively.

For each TG curve, the experimental mass losses (±5%) are similar to the proposed formulas. It is possible to verify that for all hydrated compounds, the first mass loss step is associated with the release of water molecules followed by the release of ligand molecules and sublimation of the metal chloride. Furthermore, it is verified that, considering only the release of ligand molecules (3amp, 4amp, 2mct, or 2mcp), the cadmium adducts are always more stable than the correspondent tin adducts. Since the infrared data suggest that the metal-to-ligand interaction is higher for tin adducts, this last result is an expected one, unless we take into account that the cadmium adducts generally polymerize [22–27] and so there is, probably for these compounds, the formation of cross-linking bonds, leading to more stable compounds, from a thermal point of view.

The antimicrobial effect of the adducts was measured against a variety of microorganisms including bacteria and fungus (Table 7 and Figure 5). The no-growth zones around the hole indicated the inhibiting activity of the adducts on the microbe. These were calculated and compared with the ampicillin as an antibacterial agent or amphotericin B as an antifungal agent. The adduct CdCl₂.2(2mct).H₂O and CdCl₂.(2mct) showed the highest antimicrobial activities followed by SnCl₂.(2mcp).1.5H₂O among all other adducts. On other hand, the CdCl₂.(3amt) and CdCl₂.(4amt).H₂O have no effect on any bacteria or fungal strains (Table 7). The antimicrobial activities of these adducts might be caused by a direct interaction of Cd (II) or Sn (II) ions with proteins, enzymes, nucleic acids, and membranes of microbe cells.

Table 7: Antimicrobial activities (inhibition zone diameter, mm/µg sample) of papaverine and its metal complexes against Gram-positive bacteria, Gram-negative bacteria, and two types of fungi.

The adducts
Gram-negative bacteria
Gram-positive bacteria
Fungi

E. coli
P. aeruginosa
B. subtilis
S. aureus
A. flavus
C. albicans

Control: DMSO
0.0
0.0
0.0
0.0
0.0
0.0

Ampicillin (Antibacterial agent)
22
17
20
18
0.0
0.0

Amphotericin B (Antifungal agent)
0.0
0.0
0.0
0.0
17
19

SnCl₂.(3amt).H₂O
10
10
12
11
0.0
23

SnCl₂.2(3amt).H₂O
15
13
13
15
0.0
14

CdCl₂.(3amt)
0.0
0.0
0.0
0.0
0.0
0.0

CdCl₂.2(3amt)
12
12
12
15
0.0
11

SnCl₂.(2mct).0.5H₂O
9
0.0
10
10
0.0
0.0

SnCl2.2(2mct)
9
9
9
21
0.0
0.0

CdCl₂.(2mct)
16
15
14
20
14
17

CdCl₂.2(2mct).H₂O
26
28
26
32
31
35

SnCl₂.(2mcp).1.5H₂O
16
15
16
21
0.0
9

SnCl₂.2(2mcp).4H₂O
13
14
14
14
0.0
0.0

CdCl₂.(2mcp)
11
10
11
10
0.0
16

CdCl₂.2(2mcp)
14
13
12
16
0.0
13

SnCl₂.(4amt).4H₂O
9
0.0
0.0
0.0
0.0
0.0

SnCl₂.2(4amt).1.5H₂O
10
9
12
13
0.0
9

CdCl₂.(4amt).H₂O
0.0
0.0
0.0
0.0
0.0
0.0

CdCl₂.2(4amt)
9
0.0
0.0
9
0.0
0.0

(a)

(b)

(c)

(d)

Figure 5: The antimicrobial effects of the 16 solid adducts. The number above the column indicates the inhibition zone diameter.

4. Conclusion

The adducts SnCl₂.(3amt).H₂O, SnCl₂.2(3amt).H₂O, CdCl₂.(3amt), CdCl₂.2(3amt), SnCl₂.(2mct).0.5H₂O, SnCl2.2(2mct), CdCl₂.(2mct), CdCl₂.2(2mct).H₂O, SnCl₂.(2mcp).1.5H₂O, SnCl₂.2(2mcp).4H₂O, CdCl₂.(2mcp), CdCl₂.2(2mcp), SnCl₂.(4amt).4H₂O, SnCl₂.2(4amt).1.5H₂O, CdCl₂.(4amt).H₂O, and CdCl₂.2(4amt)—where 3amt = 3-amino-1,2,4-triazole; 4amt = 4-amino-1,2,4-triazole; 2mct = 2-mercaptothiazoline; and 2mcp = 2-mercaptopyridine—were synthesized by a solid-state route and characterized by CHN elemental analysis and infrared spectroscopy. A thermogravimetric study was also performed. It is verified that, for all compounds, the monoadducts are the most stable ones. Such fact agrees with a higher ionic and covalent character of the metal-ligand bond for such compounds. From the result, it can be concluded that 14 of the 16 compounds have a good biological activity against these microorganisms.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgments

The authors are grateful to Taif University for supplying essential facilities and acknowledge the support of Taif University Researchers Supporting Project (TURSP-2020/39), Taif University, Taif, Saudi Arabia.

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