Introduction

Zinc has diverse biological functions in enzymatic catalysis, the immune system and neurons [1]. Its deficiency leads to a retardation of growth and development in children, genital development, dermatitis, poor pregnancy outcomes or decreased immune functions. Zinc deficiency is estimated to be high, with billions of people at risk, mostly in the developing world [2]. Simple zinc compounds (zinc sulphate, zinc oxide) are often used in nutritional products, pharmacy and cosmetics. They are often replaced by zinc(II) complexes, because they are not only a very good source of zinc, but also the organic ligand may have useful biological activity. Therefore, zinc(II) complexes attracted the interest of many scientists [3–5]. As a bioactive ligand in these complexes drugs (phenazone, papaverine), vitamins (nicotinamide, 2-aminobenzoic acid) or compounds with antimicrobial activity (benzoic and salicylic acid) can be used [6–9]. It was found that the substitution of hydrogen atom by halogen in aliphatic zinc(II) carboxylates increased the antibacterial activity against S. aureus and E. coli [10]. Therefore, our attention is now focused on bromobenzoatozinc(II) complexes. In our previous works, we have studied the thermal, spectral, structural and biological properties of 2-bromobenzoatozinc(II) complexes with bioactive ligands [11–13]. In the literature, 4-bromobenzoate compounds of Co(II) and Cu(II) with nicotinamide and pyridine were prepared and characterized [14–16]. Until now from 4-bromobenzoatozinc(II) complexes, only three complexes (without additional ligand [17], with diethylnicotinamide [15] or phenantroline [18]) were prepared and their structure have been solved. Neither their thermal nor biological properties were described. This omission led us to focus our attention to 4-bromobenzoatozinc(II) complexes with bioactive ligands and as a continuation of our work the synthesis, spectral, thermal and biological properties of them are presented in this article.

Experimental

Synthesis of the compounds

These A.R. grade chemicals were used for the preparation of the studied compounds: ZnCl2 (Fluka, Germany), Na2CO3 (Mikrochem a.s., Slovakia), 4-bromobenzoic acid 97% (Aldrich, Germany), urea, thiourea, nicotinamide and phenazone (Merck, Germany).

The following compounds were prepared:

  • [Zn(4-Brbenz)2(H2O)2]

  • [Zn(4-Brbenz)2(u)2]·2H2O

  • [Zn(4-Brbenz)2(tu)2]·2H2O

  • [Zn(4-Brbenz)2(nad)2]·H2O

  • [Zn(4-Brbenz)2(phen)2]

The syntheses may be expressed by the following equations:

$$ {\text{ZnCl}}_{2} + {\text{Na}}_{2} {\text{CO}}_{3} \to {\text{ZnCO}}_{3}{\downarrow} + 2{\text{NaCl}} $$
$$ {\text{ZnCO}}_{3} + 2(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COOH}}) \to {\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} + {\text{H}}_{2} {\text{O}} + {\text{CO}}_{2}{\uparrow} $$
$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ] + 2{\text{L}} \to [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} {\text{L}}_{2} ] $$

Methanol solution of 4-bromobenzoic acid (2.58 g, 97%, 12 mmol) was added to the aqueous suspension of ZnCO3, which was freshly prepared by the reaction of aqueous solution of ZnCl2 (1.35 g, 0.01 mol) and Na2CO3 (1.06 g, 0.01 mol). The reaction mixture was stirred for 1.5 h and the excess of ZnCO3 was filtered off. Then, the methanol solution of ligands (urea, thiourea, nicotinamide or phenazone) was added to the filtrate and it was refluxed for 4 h. The reaction mixture was reduced to a half of its volume at 70 °C and left to crystallize at room temperature. In a few days, crystalline complex compounds were obtained in 72–81% yields.

Instrumentation

The carbon, hydrogen and nitrogen contents in the prepared compounds was determined by the CHN analyser PERKIN ELMER 2400. The zinc content was determined using Complexone III as an agent and Eriochrome black T as an indicator.

The IR spectra of the prepared zinc complex compounds and the solid intermediates of thermal decomposition were recorded on an AVATAR 330 FT-IR Thermo Nicolet spectrometer using KBr pellets (2 mg/200 mg KBr), in the range 4000–400 cm−1.

Thermal decomposition was studied in air atmosphere using a NETZSCH STA 409 PC/PG Thermoanalyzer with the heating rate of 10 °C min−1 up to 800 °C in ceramic crucibles.

Mass spectrometer GC/MS Agilent 7890A was used for the determination of volatile products of the thermal decomposition.

Antimicrobial assay

The antibacterial activities of the studied Zn(II) complexes, organic ligands (urea, thiourea, phenazone, methyl-3-pyridylcarbamate) and 4-bromobenzoic acid were evaluated by a micro-dilution method using G+ bacteria Staphylococcus aureus CCM 3953, G− bacteria Escherichia coli CCM 3988 [19]. The effects of these compounds on the yeasts Candida albicans were determined by macro-dilution method in L-shapes tubes adapted for direct measurement of absorbance [20]. The cultures of bacteria (in Mueller-Hinton growth medium) and yeasts (Sabouraud’s growth medium) were incubated under vigorous shaking. The effect of tested compounds on the growth of filamentous fungi Rhizopus oryzae CCM F-8284, Alternaria alternata CCM F-128 and Microsporum gypseum CCM F-8342 was observed by macro-dilution technique on solidified broth medium during static culturing [21, 22] and the diameters of growing fungal colonies were measured at intervals.

Chromatographically pure compounds were dissolved in DMSO; its final concentration never exceeded 1.0 vol.% in either control or treated samples. Concentration of tested compounds was in the range of 0.01–2.0 mmol dm−3 (bacteria, yeasts) or of 0.1–3.0 mmol dm−3 (filamentous fungi) in all experiments. The antimicrobial activity was characterized by the IC50 values (concentration of a compound which in comparison to the control inhibits the growth of model microorganisms to 50%) and MIC values (minimal inhibitory concentration of a compound which inhibits microbial growth by 100%). The IC50 and MIC values were read from toxicity curves. MIC experiments on subculture dishes were used to assess the minimal microbicidal concentration (MMC). Subcultures were prepared separately in Petri dishes containing appropriate agar medium, and incubated at 30 °C for 48 h (bacteria, yeasts) and 25 °C for 96 h (filamentous fungi). The MMC value was taken as the lowest concentration which showed no visible growth of microbial colonies on the subculture dishes.

Results and discussion

The prepared compounds are white in colour, stable in air and light. The results of elemental analyses are in good agreement with the calculated ones (Table 1). The solubility of the studied compounds is presented in Table 2. In general, the prepared compounds are more soluble in polar solvents than in non-polar. The chemical formulas of prepared compounds were proposed on the basis of the results of analyses.

Table 1 Elemental analysis of the prepared zinc(II) compounds
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Table 2 Solubility of the prepared compounds
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IR spectra

The characteristic IR bands for the compounds [Zn(4-Brbenz)2(H2O)2], [Zn(4-Brbenz)2(u)2]·2H2O, [Zn(4-Brbenz)2(tu)2]·2H2O, [Zn(4-Brbenz)2(nad)2]·H2O and [Zn(4-Brbenz)2(phen)2] are reported in Table 3. The assignments were done according to the literature data [23, 24]. Apart from the compound with phenazone, every compound contains water. Absorption bands of ν(O–H) appeared in region 3516–3326 cm−1 and δ(O–H) in region 1651–1616 cm−1. The presence of aromatic system was confirmed by stretching vibration ν ar(C–H) in the region 3097–3032 cm−1, further by ν ar(C=C) at 1587–1442 cm−1 and γ ar(C–H) in region 775–765 cm−1. The absorption band of C–Br was observed at 688–618 cm−1 and stretching vibration ν(Zn–O) appeared at 473–454 cm−1. The magnitude of separation of asymmetric and symmetric stretching vibrations of carboxylate group, Δ(COO−), was used as a criterion to assign the type of the carboxylate coordination in the studied complexes. In general, the following order is proposed for divalent metal carboxylates [23, 25]: Δ(monodentate) ≫ Δ(ionic) ≥ Δ(bridging) ≫ Δ(chelating). The Δ value determined from the IR spectra of sodium 4-bromobenzoate is 171 cm−1. By comparing the values of Δ(COO−) of prepared compounds with that of sodium 4-bromobenzoate, we can assume a monodentate coordination of 4-bromobenzoate group in all compounds [Zn(4-Brbenz)2(H2O)2] (194 cm−1), [Zn(4-Brbenz)2(u)2]·2H2O (185 cm−1), [Zn(4-Brbenz)2(tu)2]·2H2O (177 cm−1), [Zn(4-Brbenz)2(nad)2]·H2O (193 cm−1) and [Zn(4-Brbenz)2(phen)2] (191 cm−1). The crystal structure of compound [Zn(4-Brbenz)2(H2O)2] is known from the literature [17]. From the structural data, it can be seen that the Zn–O bond distances are significantly different (2.010(5) and 2.468(5) Å), which leads to an asymmetric chelated coordination close to the monodentate coordination. Therefore, the value of Δ(COO−) in the IR spectrum indicates the monodentate binding mode. The presence of bioactive organic ligands was also confirmed by FTIR spectroscopy (Table 3). The strong absorption band of the carbonyl ν(C=O) vibration of compound [Zn(4-Brbenz)2(nad)2]·H2O appeared at 1701 cm−1, which is shifted to a higher wavenumber as compared with the nicotinamide νnad(C=O) = 1679 cm−1. We suppose that the pyridine nitrogen of nicotinamide is involved in coordination with zinc, therefore, the electron density is shifted towards the pyridine nitrogen, which leads to a shift of ν(C=O) to a higher value. On the other hand, in the case of compounds [Zn(4-Brbenz)2(u)2]·2H2O and [Zn(4-Brbenz)2(phen)2], the stretching vibration of the carbonyl group ν(C=O) appeared at 1661 and 1656 cm−1, respectively. These absorption bands are shifted to a lower wavenumber in comparison with the free ligands (νu(C=O) = 1670 cm−1, νphen(C=O) = 1666 cm−1). This phenomenon can be explained by the coordination of the carbonyl oxygen to the central zinc atom, leading to the decrease of the double bond character of the carbonyl group and shifting the stretching vibration of ν(C=O) to a lower value.

Table 3 Characteristic absorption bands/cm−1 in IR spectra of prepared compounds
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Thermal properties

The results of thermal analysis of studied compounds are reported in Table 4.

Table 4 Thermal decomposition of the prepared compounds
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[Zn(4-Brbenz)2(H2O)2]

The thermal decomposition starts with the release of water, which is accompanied by endothermic effect at 140 °C (exp. 6.73%, calc. 7.19%) (Fig. 1). In the next step, above 250 °C, the release of (4-BrC6H4)2CO (m/z 338, 260, 183, 155) and CO2 (exp. 76.77%, calc. 76.58%) takes place, which is accompanied with an exothermic effect in temperature range 400–670 °C. The final solid product of thermal decomposition is ZnO. It was confirmed by XRD analysis and IR spectroscopy (ν(Zn–O) = 442 cm−1).

Fig. 1
figure 1

TG–DTG–DTA curves of [Zn(4-Brbenz)2(H2O)2]

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The following equation is proposed for the decomposition process:

$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{H}}_{2} {\text{O}})_{2} ]\mathop{\longrightarrow}\limits^{120 - 190\,^\circ {\text{C}}}2{\text{H}}_{2} {\text{O}} + [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ] $$
$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ]\mathop{\longrightarrow}\limits^{250 - 630\,^\circ {\text{C}}}(4{\text{-BrC}}_{6} {\text{H}}_{4} )_{2} {\text{CO}} + {\text{CO}}_{2} + {\text{ZnO}} $$

[Zn(4-Brbenz)2(u)2]·2H2O

As it can be seen in Fig. 2, in the first stage of the thermal decomposition, the dehydration process occurs in two steps with endothermic effects on DTA curve at 90 and 130 °C (exp. 4.53%, calc. 5.80%). Above 180 °C, the release of urea (m/z 60, 44, 16) and (4-BrC6H4)2CO (m/z 338, 260, 183, 155) occurs (exp. 76.30%, calc. 74.03%) with endothermic effects at 240 and 280 °C and exothermic effect at 505 °C. Apart from the mass spectrometry, the release of urea was confirmed by IR spectroscopy of solid intermediate at 250 °C. The absence of characteristic absorption bands of urea was observed (ν(N–H) = 3345, 3212 cm−1, ν(C=O) = 1665 cm−1). In the final step of thermal decomposition, the release of CO2 (exp. 6.58%, calc. 7.08%) takes place. The solid product is zinc(II) oxide, which was confirmed by XRD analysis and IR spectroscopy (ν(Zn–O) = 490 cm−1).

Fig. 2
figure 2

TG–DTG–DTA curves of [Zn(4-Brbenz)2(u)2]·2H2O

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The decomposition process can be expressed by the following reactions:

$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{u}})_{2} ] \cdot 2{\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{85 - 180\,^\circ {\text{C}}}2{\text{H}}_{2} {\text{O}} + [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{u}})_{2} ] $$
$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{u}})_{2} ]\mathop{\longrightarrow}\limits^{180 - 550\,^\circ {\text{C}}}(4{\text{-BrC}}_{6} {\text{H}}_{4} )_{2} {\text{CO}} + {\text{CO}}_{2} + {\text{ZnO}} $$

[Zn(4-Brbenz)2(tu)2]·2H2O

Dehydration process takes place in one step up to 160 °C (exp. 4.66%, calc. 5.51%), which is accompanied with an endothermic effect at 140 °C on DTA curve (Fig. 3). In the next step, thiourea (m/z 76, 60, 16) releases in endothermic effect at 220 °C and (4-BrC6H4)2CO (m/z 338, 260, 183, 155) with a small endothermic peak at 310 °C (exp. 8.13%, 6.74%). The release of thiourea up to 230 °C was confirmed by IR spectroscopy of the solid intermediate (absence of (ν(N–H) = 3379, 3277 cm−1, δ(N–H) = 1616 cm−1). In the last step of thermal decomposition, the release of CO2 takes place (exp. 8.13%, calc. 6.74%) with exothermic effect at 510 and 600 °C. The final solid product of thermal decomposition is ZnO (exp. 11.76%, calc. 12.45%) (confirmed by IR spectroscopy (ν(Zn–O) = 440 cm−1).

Fig. 3
figure 3

TG–DTG–DTA curves of [Zn(4-Brbenz)2(tu)2]·2H2O

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The following equation expresses the thermal decomposition:

$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{tu}})_{2} ] \cdot 2{\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{95 - 160\,^\circ {\text{C}}}2{\text{H}}_{2} {\text{O}} + [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{tu}})_{2} ] $$
$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{tu}})_{2} ]\mathop{\longrightarrow}\limits^{160 - 640\,^\circ {\text{C}}}2{\text{tu}} + (4{\text{-BrC}}_{6} {\text{H}}_{4} )_{2} {\text{CO}} + {\text{CO}}_{2} + {\text{ZnO}} $$

[Zn(4-Brbenz)2(nad)2]·H2O

The thermal decomposition of this compound is shown in Fig. 4. As it can be seen, this compound is thermally stable up to 100 °C, when the release of H2O (exp. 2.43%, calc. 2.47%) occured with endothermic effect at 125 °C on the DTA curve. The dehydration step was followed by the release of nicotinamide (m/z 122, 106, 78) and (4-BrC6H4)2CO (m/z 338, 260, 183, 155) in endothermic effect at 300 °C, which was followed by the release of CO2 in a broad exothermic effect in region 400–800 °C on the DTA curve. The final solid product of thermal decomposition was ZnO (exp. 11.05%, calc. 11.18%), which was confirmed by XRD analysis and IR spectroscopy (ν(Zn–O) = 488 cm−1). The release of nicotinamide up to 290 °C was confirmed by IR spectroscopy of the intermediate (absence of (ν(N–H) = 3367 cm−1, ν(C=O) = 1701 cm−1).

Fig. 4
figure 4

TG–DTG–DTA curves of [Zn(4-Brbenz)2(nad)2]·H2O

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The thermal decomposition can be expressed as follows:

$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{nad}})_{2} ] \cdot {\text{H}}_{2} {\text{O}}\mathop{\longrightarrow}\limits^{100 - 165\,^\circ {\text{C}}}{\text{H}}_{2} {\text{O}} + [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{nad}})_{2} ] $$
$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{nad}})_{2} ]\mathop{\longrightarrow}\limits^{165 - 750\,^\circ {\text{C}}}2{\text{nad}} + (4{\text{-BrC}}_{6} {\text{H}}_{4} )_{2} {\text{CO}} + {\text{CO}}_{2} + {\text{ZnO}} $$

[Zn(4-Brbenz)2(phen)2]

Thermal decomposition of this compound starts above 200 °C by the release of phenazone (m/z 188, 173, 96) and (4-BrC6H4)2CO (m/z 338, 260, 183, 155) with endothermic effect at 330 °C (Fig. 5). The release of phenazone up to 300 °C was confirmed by IR spectrum of the solid intermediate product of thermal decomposition, where the absorption bands of phenazone (ν(C=O) = 1656 cm−1, δ(C–H) = 1454, 1318 cm−1) were missing. Above 450 °C, carbon dioxide released (exp. 5.88%, calc. 5.23%) and the final solid product of thermal decomposition was ZnO (exp. 12.02%, calc. 9.67%). It was confirmed by IR spectroscopy (ν(Zn–O) = 481 cm−1) and XRD analysis.

Fig. 5
figure 5

TG–DTG–DTA curves of [Zn(4-Brbenz)2(phen)2]

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The following equation expresses the thermal decomposition:

$$ [{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{phen}})_{2} ]\mathop{\longrightarrow}\limits^{200 - 720\,^\circ {\text{C}}}2{\text{phen}} + (4{\text{-BrC}}_{6} {\text{H}}_{4} )_{2} {\text{CO}} + {\text{CO}}_{2} + {\text{ZnO}} $$

On the basis of mass spectrum patterns the following mechanism of the fragmentation of bis(4-bromophenyl)methanone was proposed (Scheme 1).

Scheme 1
scheme 1

Fragmentation of bis(4-bromophenyl)methanone based on the mass spectrum

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The fragmentations of neutral ligands (urea, phenazone, nicotinamide and thiourea) were proposed in our last paper [13].

The results of XRD analysis correspond with the structural data of ZnO from the literature [26] and are presented in Fig. 6.

Fig. 6
figure 6

Results of powder diffractometry

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Biological properties

Biological activity of compounds were characterized by the IC50 and MIC values [mmol dm−3]. The results of microbiological tests are summarized in Table 5. It was found that neither 4-bromobenzoic acid nor any free ligand affected the growth of selected microorganisms (IC50 > 3.0 mmol dm−3, MIC > 3.0 mmol dm−3). Thus, it can be concluded that the presence of zinc(II) ion in complexes led to the increase of the inhibitory activity on the growth of selected bacteria, yeasts and filamentous fungi. In comparison with zinc(II) 4-bromobenzoate (IC50 = 0.23 mmol dm−3, MIC = 1 mmol dm−3), only the complex with thiourea [Zn(4-BrC6H4COO)2(tu)2]·2H2O (IC50 = 0.20 mmol dm−3, MIC = 1 mmol dm−3) and with nicotinamide [Zn(4-Brbenz)2(nad)2]·H2O (IC50 = 0.14 mmol dm−3, MIC = 1 mmol dm−3) had a higher inhibitory activity against G+ bacterium S. aureus. Compound [Zn(4-Brbenz)2(nad)2]·H2O (IC50 = 0.70 mmol dm−3, MIC = 2 mmol dm−3) had a higher inhibitory activity against E. coli than compound [Zn(4-Brbenz)2(H2O)2] without neutral ligand (IC50 = 0.73 mmol dm−3, MIC = 2 mmol dm−3). The presence of neutral bioactive ligands decreased the biological activity of complexes (IC50 = 0.6–2.6 mmol dm−3, MIC = 2–3 mmol dm−3) in comparison with compound [Zn(4-Brbenz)2(H2O)2] (IC50 = 0.5 mmol dm−3, MIC = 2 mmol dm−3) against C. albicans. The antifungal activity of compounds with bioactive ligands (IC50 = 0.35–0.5 mmol dm−3, MIC = 1 mmol dm−3) is higher than in zinc(II) 4-bromobenzoate (IC50 = 0.70 mmol dm−3, MIC = 1 mmol dm−3) against R. oryzae. The highest antifungal activity against A. alternata was found in the case of compound with thiourea [Zn(4-BrC6H4COO)2(tu)2]·2H2O (IC50 = 0.3 mmol dm−3, MIC = 1 mmol dm−3). Dermatophytic fungi M. gypseum was the most sensitive to compound without neutral bioactive ligand [Zn(4-Brbenz)2(H2O)2] (IC50 = 0.6 mmol dm−3, MIC = 1 mmol dm−3).

Table 5 Antimicrobial activity of prepared compounds, bioactive ligands and 4-bromobenzoic acid characterized by the values of IC50 and MIC/mmol dm−3
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Conclusions

The thermal decomposition of hydrated compounds started with dehydration process. During the thermal decomposition, the neutral organic ligand, carbon dioxide and bis(4-bromophenyl)metanone were evolved. The final solid product of the thermal decomposition was zinc oxide. The solid intermediates and volatile products of thermal decomposition were confirmed by IR spectroscopy and mass spectrometry. It was found that zinc(II) 4-bromobenzoate starts to decompose at the highest temperature and the thermal stability of anhydrous compounds decreases in the following order:

$$ \mathop {[{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ]}\limits_{{250\,^\circ {\text{C}}}} > \mathop {[{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{phen}})_{2} ]}\limits_{{200\,^\circ {\text{C}}}} > \mathop {[{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{u}})_{2} ]}\limits_{{180\,^\circ {\text{C}}}} > \mathop {[{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{nad}})_{2} ]}\limits_{{165\,^\circ {\text{C}}}} > \mathop {[{\text{Zn}}(4{\text{-BrC}}_{6} {\text{H}}_{4} {\text{COO}})_{2} ({\text{tu}})_{2} ]}\limits_{{160\,^\circ {\text{C}}}} $$

On the basis of values of Δ from IR spectra, the monodentate coordination of 4-bromobenzoate group was proposed in all compounds.

It was found that the filamentous fungi are more sensitive to the studied compounds as the selected bacteria. Compound with nicotinamide had the highest antibacterial activity. The presence of neutral ligands decreased the biological activity against C. albicans and M. gypseum. On the other hand, thiourea and phenazone increased the antifungal activity of 4-bromobenzoatozinc(II) complex compounds against A. alternata.