4-Methoxybenzaldehyde, 4-methylthiosemicarbazide, ethanol and acetic acid were used as purchased without further purification. IR spectrum was obtained from a Perkin-Elmer System 2000 FT-IR spectrophotometer using KBr pellets. NMR spectra were run in CDCl₃ on a 400 MHz spectrometer. Melting point was recorded on a Meltemp II Apparatus and is uncorrected. Elemental analysis was performed on a Thermo Flash EA-1112 Series CHNS-O Elemental Analyzer. Details of X-ray techniques and biological materials are described under their respective sections below.

A sample of 4-methylthiosemicarbazide (210 mg, 0.002 mol) dissolved in 15 ml ethanol was added to a solution of 4-methoxybenzaldehyde (0.28 mL, 0.002 mol). Five (05) drops of glacial acetic acid were added to the mixture (Scheme 1). The reaction mixture was allowed to reflux for 6 hours at a temperature of 70˚C. The clear solution which was allowed to cool, formed suitable crystals which were filtered and washed several times with ethanol for X-ray diffraction studies.

Yield: 85%. Mp: 181 - 182˚C. Anal. Calcd for C₁₀H₁₃N₃OS: C 53.78%; H 5.87%; N 18.82%; O 7.17% and S 14.36%. Experimental: C 54.14%; H 5.65%; N

Scheme 1. Synthesis of 1-(4-methoxybenzylidene)-4-methylthiosemicarbazone.

19.11%; O 7.18 and S 13.90%. IR (KBr, cm⁻¹): 3319 and 3157 (2N-H); 1600 and 1507 (C=C of the aromatic ring); 1543 (C=N); 1177 (C=S); 850 (N-N) and 828 (p-disubstituted benzene ring). ¹H NMR (δ ppm): 3.18 (CH₃-N); 3.77 (CH₃O); 6.85 (2H, J = 11 Hz, meta H); 7.45 (2H, J = 11 Hz, ortho H); 7.20 (N-H at position 4); 7.70 (CH=N) and 9.40 (N-H and position 2). ¹³C NMR (δ ppm): 178.3 (C=S); 161.6 (C=N); 142.3 (para C); 128.7 (ortho C); 125.9 (C-1’) 114.4 (meta C); 55.4 (CH₃-O) and 31.2 (CH₃-N).

This was performed using standard procedures as reported by Nfor et al. [19] . Briefly, suitable-single crystal of MBT was mounted in air unto a loop. The data collection for MBT was carried out with a Bruker DUO APEX II CCD diffractometer at temperature controlled using an Oxford cryostream-700. Data reduction and cell refinement were performed using SAINT-Plus, and the space group was determined from systematic absences by XPREP and further justified by the refinement results. Graphite monchromated MoKα (λ = 0.71073 Å) radiation was used. The X-ray diffraction data have corrected for Lorentz-polarization factor and scaled for absorption effects by multi-scan using SADABS. The structure was solved by direct method, implemented in SHELXS-97. Refinement procedure by full-matrix least-square method based on F² values against reflections have been performed by SHELX-97, including anisotropic displacement parameters for all non-H atoms. The positions of hydrogen atoms belonging to the carbon atoms were geometrically optimized by applying a riding model. CCDC 1556045 contains the supplementary crystallographic data for this paper. Calculations concerning the molecular geometry, the affirmation of chosen space groups and the analysis of hydrogen bonds were performed with PLATON. The molecular graphic was done with ORTEP-3 and Mercury (version 3.0).

The elemental analysis for C, H, N and S revealed that the calculated and experimental data for the Schiff base are in good agreement suggesting the high percent purity of the compound.

The infrared spectrum (Figure S1) was taken in 4000 - 400 cm⁻¹ region. Two bands between 3319 and 3157 cm⁻¹ represent stretching frequencies for the two N-H groups. A band at 828 cm⁻¹ indicating the presence of a p-disubstituted benzene ring. Other important bands were observed at 1543 cm⁻¹ (C=N) and 1177 cm⁻¹ (C=S).

The ¹H NMR spectrum (Figure S2) of 1-(4-methoxybenzylidene)-4-methylthi- osemicarbazone was recorded in CDCl₃. Prominent peaks were observed at 3.18 which was assigned to CH₃-N, 3.77 attributed to the methoxy group (CH₃O), 6.85 (2H, J = 11 Hz, meta H), 7.45 (2H, J = 11 Hz, ortho H) and 7.70 (CH=N).

The ¹³C NMR spectrum (Figure S3) of 1-(4-methoxybenzylidene)-4-methylthi- osemicarbazone was recorded in CDCl₃. The most deshielded peak appeared at 178.8 ppm and was attributed to C=S, followed by a peak at 161.6 ppm which was assigned to C=N. Signals for the aromatic carbon atoms were observed in the range, 142.3 - 125.9 ppm while the methoxy carbon atom resonated at 55.4 ppm and CH₃-N appeared at 31.2 ppm.

The molecular structure of the Schiff base is shown in Figure 1 along with the atomic numbering scheme. The Schiff base crystallises in the orthorhombic system in space group Pbca. The unit cell dimensions are a = 13.3144 (13) Å, b = 8.9064 (9) Å and c = 18.6349 (18) Å with the cell angles being α = 90˚, β = 90˚ (2) and χ = 90˚. The Z value is equal to 8.

The crystal structure of the molecule is in line with the IR, NMR and elemental analysis data of the molecule. The bond distances and angles are listed in Table 1 and are comparable to those reported in the literature for similar compounds [22] . The crystal structure refinement data for MBT are listed on Table 2.

MBT was tested against four isolates of Salmonella species, namely Salmonella typhi (ST), Salmonella paratyphi A (SPA), Salmonella paratyphi B (SPB), Salmonella typhimurium (STM) and one strain of Salmonella typhi (ATCC 6539).

The data obtained from this test (Table 3) showed that MBT exhibited the various Salmonella species, with the MIC values ranging from 64 to128 μg/mL. STs, SPA and STM presented MBCs equal to 128 µg/mL and MBCs/MICs ratio equal to 2.

In fact, according to the criteria described by Kuete [23] , activities of isolated product are significant when MIC ≤ 10 μg/mL, moderate when 10 < MIC ≤ 100 μg/mL, weak when MIC > 100 μg/mL. Therefore, MBT is active and possesses moderate inhibitory potential vis-à-vis STs, SPA and STM. Antimicrobial substances are considered as bactericidal agents when the ratio MBC/MIC ≤ 4, and bacteriostatic when the ratio MBC/MIC > 4 [16] [24] . For MBT, the ratio MBC/ MIC was <4 against most of the bacteria tested, suggesting that this product may be classified as bactericidal agent against these bacteria.