Ni(II), Cu(II), Mn(II), and Fe(II) Metal Complexes Containing 1,3-Bis(diphenylphosphino)propane and Pyridine Derivative: Synthesis, Characterization, and Antimicrobial Activity

Four of the coordination compounds of the general formula, [M(DPPP)(APY)(H2O) Cl2].xH2O, where M = Ni(II), Cu(II), Mn(II), and Fe(II) and x = 0, 1, or 2 molecules of H2O, DPPP = 1,3-bis(diphenylphosphino)propane, and APY = 2-aminopyridine, have been prepared and characterized. The structure of the complexes has been confirmed by elemental analysis, FT-IR, and UV-Vis spectral data. Thermal analysis (thermogravimetry, derivative thermogravimetry, and differential thermal studies) has been used to study the thermal decomposition stages. Biological activity of all synthesized complexes was tested against five bacterial strains and three fungal strains. Bacteria and fungi strains are common contaminants of the environment in Saudi Arabia, some of which are frequently reported from contaminated water, soil, and food.


Introduction
Coordination compounds have been known since the beginning of modern chemistry; also, coordination compounds are so common that their structures and reactions are described as in many ways. e atom within a ligand is bonded to the central metal atom. Especially in hydrometallurgy, the coordination chemistry of the metals participate plays a large role in their solubility and reactivity, as the ore is refined into a precious transition elements. Diphosphine ligands, such as 1,3-bis(diphenylphosphino) propane, are organophosphorus compounds, and these compounds are white solids that are soluble in organic solvents. It is also degraded in air to phosphine oxide and slightly air-sensitive. It is classified as a diphosphine ligand in coordination chemistry and homogeneous catalysis [1][2][3]. e mixed use of metal complexes containing diphosphines and other ligands, which consist of N or S atoms have been intensively inspected during the past years because of their possibility applications in the fields of light emitting devices, biological activity, and catalysis [4][5][6][7][8]. Additionally, a pronounced attention has been induced by the investigation of the new bioactivity of metal-organic framework materials (BIOMOFs) contained in construction materials as potential antifungal and antibacterial materials (e.g., antifungal glass, antibacterial coating, or antibacterial) [9][10][11][12][13][14]. Diphosphines are essential ligand backbones, which are coordinated to the metal via monodentate or bidentate manner, and these ligands were used in the development of biologically active metal coordination complexes [15][16][17][18]. Pyridine derivatives avail as useful chelating ligands in a large form of inorganic and organometallic applications, and additions act as monodentate ligands that coordinate transition metal ions (N-Ni, N-Cu, Mn-N, and Fe-N) occupy an important position in organometallic chemistry. In addition, there are several reports on pyridine derivative compounds in which the amino group (NH 2 ) also participates in coordination [19][20][21][22][23]. In view of the above importance of these ligands and its complexes, we report in this work on the synthesis and characterization of Ni(II), Cu(II), Mn(II), and Fe(II) coordination compounds with DPPP and APY. e structures of the ligands are presented in Figure 1.

Physical Measurements.
e chemical analyses, CHN, were performed using, Analyischer Functions test Var. El Fab Nr. (11982027) elemental analyzer. FT-IR were recorded as potassium bromide disks (400 to 4000 cm −1 ) with a FT-IR spectrophotometer and the UV-Vis spectra were obtained using a Shimadzu (UV-2101) PC spectrophotometer. Magnetic susceptibility measurements were done on a magnetic susceptibility balance of the type (MSB-Auto). e conductance of the complexes was measured using a conductivity meter model (4310, JENWAY). ermal analysis of the compounds was carried out in dynamic air on a Shimadzu (DTG 60-H) thermal analyzer at a heating rate (10°C min −1 ).

Bacterial and Fungal Strains.
e antimicrobial activity of different four complexes extracts was evaluated using five bacterial strains and three fungal strains. ree strains of gram-positive cocci (Staphylococcus epidermidis, Enterococcus faecalis, and Staphylococcus aureus), two strains of gram-negative bacilli (Escherichia coli, and Pseudomonas aeruginosa), one stain of yeast-like fungi (Candida albicans), and 2 molds (Aspergillus fumigatus and Aspergillus flavus) were used in this study.

Inoculum Preparation.
Bacterial and yeast-like fungal inoculum were prepared from fresh pure cultures in Muller Hinton broth. Each bacterial and yeast-like fungal suspension were compared with 0.5 McFarland standard. Mold samples were inoculated directly into Sabouraud dextrose agar.

Agar Diffusion Assay.
e antimicrobial activity of different chemical complex extracts against the selected microorganisms was evaluated using the agar diffusion assay. Each bacterial inoculum was spread on to two Mueller-Hinton agar plates using a sterile cotton swab by lawn culture technique, and the mold samples were inoculated directly onto Sabouraud dextrose agar. After inoculation, wells were made with the help of a sterile cork borer; three wells were made in one of the agar plates for extract numbers 1-3, and four wells were made in the second plate for extract numbers 4-7. en, each extract (100 µl) was added to already marked well. e plates were then incubated for 18-24 hrs at 37°C. After incubation, we observed the zone of inhibition around the wells and measured the zone diameter in millimeters (mm) by a ruler.  (2). e complex was synthesized by adding the CuCl 2 .2H 2 O solution (0.82 g, 4.8 mmol) in 20 mL distilled water to 2g (4.8 mmol) of 1,3-bis(diphenylphosphino)propane in 10 mL of CH 2 Cl 2 in the presence of NaOH (0.1 M). en, to the mixture solution, a 15 mL ethanolic solution of APY (0.45 g, 4.8 mmol) was added immediately. e mixture was refluxed for 3 h and then left aside at room temperature. A light green color was produced and the latter was separated and washed with H 2 O and ethanol.

Preparation of [Mn(DPPP)(APY)(H 2 O)Cl 2 ] Complex (3).
e Mn(II) complex was prepared by adding the metal salt MnCl 2 .4H 2 O (0.87 g, 4.4 mmol) dissolved in 20 mL of distilled water with DPPP ligand (1.8 g, 4.4 mmol) dissolved in about 15 mL of a solution (1 : 2 MeOH/CH 2 Cl 2 ) in the presence of NaOH. e subsequent process was the addition of a 10 ml ethanolic solution of APY ligand (0.41 g, 4.4 mmol). e mixture was refluxed for about 4 h and then cooled. e dark-brown color formed separated, which was filtered and washed with EtOH and dried over P 2 O 5 . (4). A 1,3-bis(diphenylphosphino)propane (2g, 4.8 mmol) was dissolved in 15 mL of a solution (1 : 2 MeOH/ CH 2 Cl 2 ) in the presence of sodium hydroxide and then the metal salt FeCl 2 (0.61 g, 4.8 mmol) was added in 15 mL of distilled water followed by addition 15 mL ethanolic solution of 2-aminopyridine (0.45 g, 4.8 mmol), and the resultant product was refluxed for 4 h and then cooled and filtered. Light-yellow precipitate formed and was collected.

Results and Discussion
e nickel(II), copper(II), manganese(II), and iron(II) coordination compounds were prepared by the reaction of 1,3bis(diphenylphosphino)propane with metal salts and 2aminopyridine. e prepared four compounds were found to react in the molar ratio 1 : 1: 1 metal: DPPP: APY. In addition, these compounds are air stable and insoluble in common organic solvents but sparingly soluble in dimethylsulphoxide. e conductivities of the compounds were measured in DMSO using 10 −3 M solutions of the complexes. e molar conductivity values of the transition metal compounds were 59, 40, 32, and 52 Λm Scm 2 mol −1 ), respectively. e compositions of the complexes supported by the elemental analysis are recorded together with color in Table 1.

FT-IR Spectra.
e main infrared spectra of these compounds are listed in Table 2. A comparison of the FT-IR spectra of the complexes 1, 2, 3, and 4 with those of the free DPPP and APY ligands reveals interesting features relating to the metal-ligand (M-L) interactions. From the FT-IR spectra, it is found that the P-PH band, which shows at 1440 cm −1 in the spectrum of DPPP, is shifted to a lower wave number (1430-1434 cm −1 ), indicating a sharing of this group in the bonding with the metal ions [24]. e stretching frequencies of ](NH 2 ) are observed at 3440 cm −1 in all complexes; the spectrum almost undergoes no shift, indicating the nonparticipation of this group in the coordination [25]. On the other hand, the stretching vibration of pyridine group located at 1617 (]) C � C and 1473 (]) C � N cm −1 in the APY ligand exhibits a notable shift to a wave number (1608-1624) and (1478-1482 cm −1 ) in all complexes, respectively [25]. e C-N stretching in the ring bands of the APY ligand are shifted to lower wave numbers in the range of 1024-1030 cm −1 [25]. In the IR spectrum of the free APY, υ(C-NH 2 ) occurs at 1140 cm −1 with no shift in the spectra of the complexes [26]. ese results confirm that the pyridine groups are coordinated to the metal ions as a monodentate through the N-atom. e very strong band for the P-C vibration of free forms of phosphine ligand displays a shift from 690 cm −1 to a lower wave number (681-694 cm −1 ) [27]. e bands between 2850-2923 and 3020-3046 cm −1 are due to the absorption of the phenyl and CH 2 groups [27]. From these discussions, it is concluded that DPPP coordinates to the metal ions in a bidentate mode through phosphorus atoms. A broad diffused band with medium intensity located in the range 3488-3496 cm −1 may be assigned to ](OH) in the lattice H 2 O in (1) and (4) complexes [28]. For the complexes 1-4, the ]OH stretching vibration of coordinated H 2 O appears at the 3315-3360 cm −1 region [29]. e IR spectra of the complexes 1-4 appear as a band at 734-739 cm −1 assigned to ρ(H 2 O), which indicates the presence of coordinated water [18]. Metal-oxygen, M-nitrogen, and M-phosphorus vibration bands appear at 504-510, 470-482, and 432-448 cm −1 district, respectively ( Figure 2) [30,31].

Electronic Spectra.
e UV-Visible spectra of the complexes have been registered in dimethylsulphoxide. e results are manifested in Table 3.
e spectra show two distinct bands in the ranges 36,764-39,840 cm −1 and 29,325-32,573 cm −1 , which attributed to π ⟶ π * and n ⟶ π * transitions within DPPP and APY moieties, respectively [27,32,33]. On the other hand, in the visible region of spectra, there are characteristic bands attributed to d-d transitions for Ni(II), Cu(II), Mn(II), and Fe(II). For Ni(II), the band is located at the 19,920 cm −1 region which is assigned to d-d transition. is band is typical for the octahedral Ni(II) complexes. In the visible spectra of Cu(II), Mn(II), and Fe(II) complexes, the d-d bands are observed in 20,161, 20,040, and 19,841 cm −1 , respectively, as expected for octahedral Cu(II), Mn(II), and Fe(II).

Magnetic Moments.
e magnetic moments of the complexes were measured. e Ni(II) complex has a magnetic moment located in the range 3.20 BM. As foretelled for a high spin d 8 system with two unpaired electrons which falls in the range expected for octahedral Ni(II) compounds [34]. Copper(II) complex gave a value of magnetic moment 1.74 BM [34]. e magnetic moment of the iron complex (5.46 BM) measured at room temperature suggests a high spin d 6 configuration of octahedrally coordinated Fe 2+ ions [35]. In the case of Mn(II) a compound the value of the magnetic moment 5.30 BM typical for high spin d 5 system with five unpaired electrons with octahedral arrangement around Mn(II) [34,36]. From the foregoing data, the structure of the compounds can be postulated as follows (Figures 3 and 4).  At this step, a DTG peak appears at 70°C and a broad endothermic effect is recorded in the DTA trace at 73°C. e second step represents a detachment of APY ligand as indicated by mass loss consideration (calc. 14.27%, found 14.05%). is step is manifested in the DTG curve as a peak at 258°C and the DTA trace furnishes an exothermic effect at 260°C. e decomposition of the rest complex proceeds in    ). It has a DTG peak at 80°C corresponding to an endothermic peak at 82°C in the DTA trace. In the 2nd step, elimination of the (APY) ligand occurs (calc. 14.46%, found 13.98%). A DTG peak at 296°C with a corresponding broad exothermic peak at 298°C in the DTA trace is observed. e third step represents the thermal decomposition of the rest of the complex. e final product of the compound is compatible with MnO (calc. 10 e 1st mass loss correlates well with the corresponding of three water molecules, namely, two crystalline and one coordinated, and this may be attributed to an ion-dipole interaction between iron and water (calc. 7.86%, found 7.27%). is step (DTG peak at 81°C) is characterized by an endothermic peak in the DTA curve at 83°C. e second, third, and fourth steps correspond to the decomposition products of the remaining ligands. e final product is assigned to be FeO as indicated by the mass loss in the TG curve (calc. 10.44%, found 10.32%).

Kinetic Studies.
Nonisothermal kinetic study of the four coordination compounds was carried out applying the Coats-Redfern and Horowitz-Metzger methods (Figures 6-8). e kinetic parameters for all complexes are calculated for the first, second, and third steps according to the Coats-Redfern method and are cited in Tables 4 and 5.

Decomposition Rate and Stability of the Complexes.
e decomposition rates of the four complexes have concluded the plotting of the fraction decomposition (α) against the temperature (T) of the decomposition for the first stage as shown in (Figure 8) e stabilities of the Ni(II), Cu(II), Mn(II), and Fe(II) coordination complexes could be correlated. In addition to that, the following are the stability orders of the four complexes and the decomposition rates are based on the following: (i) e stability order at the initial temperature of the 1 st stage of the anhydrous complexes (ii) e temperature of the inflection point (iii) DTG maximum temperatures (decomposition rate) and initial temperatures (sequence of stability) that are in parentheses (iv) e regression of the curves (α against T) indicates that the complexes decompose by various decomposition rates based on the respective metal ions       International Journal of Biomaterials compounds turn on the effect of the structure, each of the metal ions on the thermal stability of the coordination compounds. e (a +Ve) values of ∆G * indicated that during the decomposition, reaction is not spontaneous ( Table 6).

X-Ray Powder Diffraction of the Four Complexes.
e X-ray powder diffraction types were recorded for the complexes 1-4. e diffraction shapes indicate that the four compounds are crystalline (Figures 9-12). e crystal data for nickel(II), copper(II), Mn(II), and Fe(II) mixed-ligand coordination complexes belong to the monoclinic, triclinic, and monoclinic crystal system, analyzed by Scherrer's equation. e crystal data for all compounds are listed in Table 7.

Biological Activity of the Coordination Compounds.
Prepared compounds of nickel(II), copper(II), manganese(II), and iron(II) were tested for in vitro antimicrobial activity and evaluated against selected bacterial and fungal strains (Figures 13-18).
ree strains of gram-positive cocci (Staphylococcus epidermidis, Enterococcus faecalis, Table 6: ermodynamic parameters for the thermal decomposition of the compounds.

Complex
Step ΔS * kJ mol −     International Journal of Biomaterials        other tested extract complexes as stated in Table 8. e zone of inhibition around the wells is measured in millimeters (mm) by a ruler.

Conclusion
A number of new one-dimensional nickel(II), copper(II), manganese(II), and iron(II) metal supramolecular coordination compounds of 1,3-bis(diphenylphosphino)propane and 2-aminopyridine have been prepared and characterized by various spectral and physical techniques. From the X-ray analysis, different crystal systems, monoclinic, triclinic, and orthorhombic system for the complexes, were found. e results of antimicrobial activity observed good biological activity for the four compounds, but the nickel(II) complex was over the other three complexes.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest. International Journal of Biomaterials 11