Development of Ferromagnetic Materials Containing Co2P, Fe2P Phases from Organometallic Dendrimers Precursors

The development of synthesis methods to access advanced materials, such as magnetic materials that combine multimetallic phosphide phases, remains a worthy research challenge. The most widely used strategies for the synthesis of magnetic transition metal phosphides (TMPs) are organometallic approaches. In this study, Fe-containing homometallic dendrimers and Fe/Co-containing heterometallic dendrimers were used to synthesize magnetic materials containing multimetallic phosphide phases. The crystalline nature of the nearly aggregated particles was indicated for both designed magnetic samples. In contrast to heterometallic samples, homometallic samples showed dendritic effects on their magnetic properties. Specifically, saturation magnetization (Ms) and coercivity (Hc) decrease as dendritic generation increases. Incorporating cobalt into the homometallic dendrimers to prepare the heterometallic dendrimers markedly increases the magnetic properties of the magnetic materials from 60 to 75 emu/g. Ferromagnetism in homometallic and heterometallic particles shows different responses to temperature changes. For example, heterometallic samples were less sensitive to temperature changes due to the presence of Co2P in contrast to the homometallic ones, which show an abrupt change in their slopes at a temperature close to 209 K, which appears to be related to the Fe2P ratios. This study presents dendrimers as a new type of precursor for the assembly of magnetic materials containing a mixture of iron- and cobalt-phosphides phases with tunable magnetism, and provides an opportunity to understand magnetism in such materials.


Introduction
Magnetic materials have recently attracted significant research interest, as they often show novel and improved properties over their bulk counterparts [1][2][3]. It is of scientific and practical significance in many fields ranging from advanced technology to biomedical applications [4][5][6][7][8]. Indeed, the synthesis of new magnetic materials remains an inspiring goal for many research groups [9]. Among the various magnetic materials applied in science, industry, and technology are transition metal phosphide (TMP) complexes, such as Fe 2 P, FeP, Co 2 P, CoP, Ni 3 P, Ni 2 P [10][11][12]. These materials are compounds between phosphorous and transition metals that combine physical properties, such as the hardness and strength of ceramics, with electronic and magnetic properties similar to metals [13]. Lately, the synthesis of magnetic TMP structures has become a promising approach to explore magnetic properties due to the formation of unusual magnetic fields, generation

Syntheses and Characterization of Homometallic Dendrimers
Five generations of homometallic dendrimers containing an alkyne group throughout their branches were synthesized using a divergent synthetic method, and a good yield was gained at around 87%. Steglech esterification reaction was used interchangeably with nucleophilic aromatic substitution reaction (S N Ar) to build dendrimer generations (Schemes 1-4). Dendrimers' structures were confirmed by 1 H, 13 C NMR spectroscopy, IR, and element analysis. Also, the thermal stability was characterized using TGA.

Syntheses and Characterization of Homometallic Dendrimers
Five generations of homometallic dendrimers containing an alkyne group throughout their branches were synthesized using a divergent synthetic method, and a good yield was gained at around 87%. Steglech esterification reaction was used interchangeably with nucleophilic aromatic substitution reaction (SNAr) to build dendrimer generations (Schemes 1-4). Dendrimers' structures were confirmed by 1 H, 13 C NMR spectroscopy, IR, and element analysis. Also, the thermal stability was characterized using TGA.
Moreover, two small peaks were observed around 4.72 and 4.11 ppm in complex 2, which indicate CH 2 protons from the alkyne moieties attached to the carboxylic-and alcohol-end groups, respectively. These peaks were observed as a small broad peak at 4.76 ppm in G2-D3, G3-D5, G4-D7, and G5-D9, which confirms the success of the esterification reaction. Additionally, in terminal carboxylic group dendrimers, one peak at 5.21 ppm corresponding to the Cps protons was observed. In the chloro-end group dendrimers, two peaks were found at 5.21 and 5.28 ppm corresponding to the inner and outer Cps protons. It is also important to state that both Cp peaks showed integration in agreement with the ratio of Cp protons in the periphery attached either to chloro-arenes or to those in the inner attached to etheric oxygen groups. The integration of the peaks indicates which peak represents the inner and which one represents the outer Cp groups. The disappearance of the OH peak of the carboxylic group in the 1 H NMR spectrum of G2-D3, G3-D5, G4-D7, and G5-D9 is another indication of a successful esterification reaction between G1-D2, G2-D4, G3-D6, and G4-D8 and complex 2. This peak resonated at 12.06 ppm in G2-D3, G3-D5, G4-D7, and G5-D9 dendrimers, and due to the formation of the ester group, the peak has been omitted. This observation confirmed the successful formation of higher-generation dendrimers.
Successful synthesis of five generations of dendrimers was also confirmed by using 13 C NMR spectroscopy. For instance, a carbonyl group with three signals at 175.48, 173. 33 and 171.23 ppm were detected in most of the homometallic dendrimers' spectra. Although three carbonyl peaks were expected in the G1-D1 and G2-D3 of chloro-end group homometallic dendrimers, only two signals were recorded at 170.25 and 173.02 ppm. The peak at 170.25 ppm was attributed to overlapped peaks of the carbonyl carbons of the ester linkages of the first and second generations of chloro-end group dendrimers, and one at 173.02 ppm referred to the ester linkage of the core. Similarly, a single peak in the dendrimers G1-D2 and G2-D4 corresponding to the Cp carbons around 78.70 and 78.68 ppm was observed. Two distinct Cp carbon peaks around 80.21 and 78. 68 ppm appeared in the higher generation dendrimers due to the growth of these generations.
Furthermore, the complexed CH aromatic appeared between 87.97 and 73.57 ppm, while the uncomplexed CH aromatic occurred between 134.18 and 107.25 ppm, and the C≡C carbons were detected around 53.92 and 49.76 ppm. The ATR-FTIR absorption spectra of the homometallic dendrimer exhibited the presence and characteristic bands of hydroxyl, ester, and ether groups, around 3315, 1705, and 1223 cm −1 , respectively. Elemental analysis has further confirmed the formation of the homometallic dendrimer, as outlined in the experimental section.

Synthesis of Heterometallic Dendrimers
As described above, reacting carboxylic-end dendrimers with complex 2 resulted in peripheral chloro-end group dendrimers containing alkyne groups (Schemes 1-4). The free chloro-terminal group advantages allow further functionalization, whereas alkyne moiety can permit post-modification with a second metallic moiety. Four generations of a heterometallic dendrimer (HETERODEN1, HETERODEN2, HETERODEN3, and HET-ERODEN4) were synthesized via a three-step synthetic procedure. First, HETERODEN1 was synthesized via nucleophilic substitution reaction of dendrimer G1-D1 with 5-(4hydroxyphenyl) pentanoic acid in the presence of K 2 CO 3 as a catalyst to obtain G1-D2; which upon Steglich esterification reaction with complex 2 yielded the G2-D3 (Scheme 1). In the final step, dicobalt hexacarbonyl was incorporated into G1-D3 via exploiting the alkyne bonds' reactivity with cobalt octacarbonyl (Scheme 5). The reaction was left to stir for 72 h to incorporate Co 2 (CO) 6 completely. Higher generations of heterometallic dendrimers (HETERODEN2, HETERODEN3 and HETERODEN4) were synthesized following similar procedures (Schemes 6-8).
The success of the synthesis of heterometallic dendrimers was monitored using 1 H and 13 C NMR spectroscopies and IR spectroscopy and elemental analyses. For example, the 1 H NMR spectrum of homometallic dendrimer G1-D2 showed one peak at 6.24 ppm due to the equivalent environment of the iron-complexed arene ligand, which indicates a successful nucleophilic aromatic substitution reaction [40,41]. Furthermore, the resonance of carboxylic acid proton disappeared from the 1 H NMR spectrum of G2-D3, indicating successful esterification between the complex 2 and G1-D2. After coordinating Co 2 (CO) 6 into G2-D3, the 1 HNMR of HETERODEN1 reveals that the methylene protons resonance shifted downfield from 4.76 ppm to 5.62 ppm due to electron deshielding caused by the cobalt [42,43]. This finding is consistent with data obtained previously [41].  Again, as indicated in previous reports [30,[41][42][43], carbonyl carbons of the Co 2 (CO) 6 moieties were detected at 193.71ppm in the 13 C NMR spectrum of HETERODEN1. Additionally, it is interesting to mention that in the 13 C NMR spectrum of HETERODEN1, the resonance of all cobalt-coordinated carbons was broadened [41]. Thus, these carbons were not visible in the 13 C NMR spectrum due to this broadening. These observations suggested that Co 2 (CO) 6 was successfully incorporated into the dendrimer branches. It is important to note that high generations of the heterometallic dendrimers (HETERODEN2, HETERODEN3, and HETERODEN4) were partially soluble in common laboratory solvents. Therefore, their characterization using 1 H and 13 C NMR was precluded, but we successfully obtained ATR-FTIR spectra and CH analysis data to ensure their successful synthesis. For example, in the ATR-FTIR spectrum of heterometallic dendrimers, three characteristic bands for the CO stretching at 2097, 2057, and 2030 cm −1 , were observed as previously mentioned [43]. All carbons in these three peaks indicated Co 2 (CO) 6 presence in the heterometallic dendrimers ( Figure 1). The thermal analysis of the HOMODENs and HETERODENs was conducted using thermogravimetric analysis (TGA) under nitrogen at a heating rate of 10 • C/min. From the TGA thermogram, it is evident that the HETERO-DEN1-HETERODEN4 began to degrade at 80 • C (Figure 2), due to the decomposition of the alkyne-hexacarbonylcobalt moieties Co 2 (CO) 6 , which is lower than the starting temperature of 200 • C for the same dendrimers without Co 2 (CO) 6 . These findings confirmed that Co 2 (CO) 6 was successfully coordinated to the dendrimers.

Characterization of Magnetic Particles Containing TMPs Phases
Pyrolysis of the homometallic and heterometallic dendrimers in a tube furnace at 900 • C in an inert atmosphere resulted in ferromagnetic materials containing multimetallic phosphide phases in a small yield (30%). The low yield can be explained by the fact that a large portion of the dendrimers consists of flexible aliphatic fragments, which evaporate at high temperatures as gases [41]. Powder X-ray diffraction (XRD), SEM and EDX, BF-STEM, TEM, and HRTEM were used to gain insight into the morphology and bulk composition of the produced magnetic materials. The success of the synthesis of heterometallic dendrimers was monitored using 1 H and 13 C NMR spectroscopies and IR spectroscopy and elemental analyses. For example, the 1 H NMR spectrum of homometallic dendrimer G1-D2 showed one peak at 6.24 ppm due to the equivalent environment of the iron-complexed arene ligand, which indicates a successful nucleophilic aromatic substitution reaction [40,41]. Furthermore, the resonance of carboxylic acid proton disappeared from the 1 H NMR spectrum of G2-D3, indicating heterometallic dendrimers (Figure 1). The thermal analysis of the HOMODENs and HET-ERODENs was conducted using thermogravimetric analysis (TGA) under nitrogen at a heating rate of 10 °C/min. From the TGA thermogram, it is evident that the HET-ERODEN1-HETERODEN4 began to degrade at 80 °C ( Figure 2), due to the decomposition of the alkyne-hexacarbonylcobalt moieties Co2(CO)6, which is lower than the starting temperature of 200 °C for the same dendrimers without Co2(CO)6. These findings confirmed that Co2(CO)6 was successfully coordinated to the dendrimers.

Characterization of Magnetic Particles Containing TMPs Phases
Pyrolysis of the homometallic and heterometallic dendrimers in a tube furnace at 900 °C in an inert atmosphere resulted in ferromagnetic materials containing multimetallic phosphide phases in a small yield (30%). The low yield can be explained by the fact that a large portion of the dendrimers consists of flexible aliphatic fragments, which evaporate at high temperatures as gases [41]. Powder X-ray diffraction (XRD), SEM and EDX, BF-STEM, TEM, and HRTEM were used to gain insight into the morphology and bulk composition of the produced magnetic materials.

X-ray Powder Diffraction (XRD)
X-ray powder diffraction (XRD) patterns of magnetic particles exhibit the XRD pattern of the homometallic (top) and heterometallic (bottom) (Figure 3). The high number of Bragg peaks observed, especially on the homometallic materials, denotes that the samples are multiphasic complexes. In order to clarify the type and amount of the distinct crystalline phases contained in the samples, the whole pattern profile fit (WPPF) of every XRD pattern has been performed using the Rietveld method (RM) (see Figures S1 and S2). In this sense, Tables S1 and S2 show the refined lattice parameters of the different struc- X-ray powder diffraction (XRD) patterns of magnetic particles exhibit the XRD pattern of the homometallic (top) and heterometallic (bottom) (Figure 3). The high number of Bragg peaks observed, especially on the homometallic materials, denotes that the samples are multiphasic complexes. In order to clarify the type and amount of the distinct crystalline phases contained in the samples, the whole pattern profile fit (WPPF) of every XRD pattern has been performed using the Rietveld method (RM) (see Figures S1 and S2). In this sense, Tables S1 and S2 show the refined lattice parameters of the different structures used in the WPPF for homometallic and heterometallic particles, respectively. Further, weight percentages and for these crystalline phases identified on each magnetic sample are listed in Tables 1 and 2. In contrast to the amorphous dendrimer precursor, the magnetic materials were polycrystalline, consisting of various nanocrystals embedded in an amorphous matrix. The X-ray powder diffraction technique [44] shows that the heterometallic samples were more crystalline than homometallic ones, with degrees of crystallinity, ranging from 75 to 86%. The crystals were large as indicated by several sharp peaks around 2θ = 16-36 • in the diffractograms, and their sizes were greater than 50 Å as determined by the Scherrer equation [45] (Tables S3 and S4).   Concerning homometallic samples, the structural characterization derived from XRD patterns analysis shows that the magnetic particles are formed mainly by iron phosphides and phosphates. Only a few weight percentages (below 5%) of metallic iron was determined for the first-and second-generation complexes. On the other hand, the heterometallic samples present a higher number of metallic structures, which include close-packed structures as face-centered cubic (FCC), hexagonal close-packed (HCP) and body-centered cubic (BCC). Besides that, about 35-50% wt of cobalt phosphide (2/1) is also established in both forms. It is worth noting that every structural determination is focused only on crystalline phases, so amorphous material such as the carbon matrix or even other phases not identified were not quantified.

Electron Microscopy Studies
The chemical composition, morphology, and particle size distribution of homometallic and heterometallic samples have been investigated by SEM and EDS analysis (Figure 4), which verified the plate-like morphology of the particles with an extensive size distribution. Also, it confirmed the presence of iron, phosphorus, and oxygen for the homometallic samples and the additional doped cobalt for heterometallic ones. The homometallic G1 and G3, heterometallic G2 and G3 samples were selected for BF-STEM, TEM, and HRTEM studies. The elemental mapping ( Figure 5) emphasizes the heterogeneous dispersion of the EDS detected elements of two systems. Overall, these results are highly consistent with the PXRD analysis. TEM and HRTEM micrographs ( Figure 6) of samples indicate the crystalline nature of the nearly aggregated particles. Selected area electron diffraction (SAED) patterns (Figure 6d,h,l,p) exhibited a polycrystalline nature of homometallic samples and reflected single-crystalline diffraction for heterometallic ones.

Magnetic Properties
An initial examination of the magnetic properties of particles using a magnetic stir bar indicated some kind of inducted magnetism because the samples were attracted to the magnetic bar. To further understand their magnetic properties, an EV9 Microsense Vibrating Sample Magnetometer (VSM) was used to get the magnetization curve (Figure 7), which depicts the magnetization vs. applied magnetic field M(H) measured at room temperature (RT) for homometallic (top) and heterometallic (bottom) materials. Except for G3 and G4 on homometallic samples, the rest of the samples exhibit a typical hysteresis loop characteristic of ferromagnetic substances, which separate increasing and decreasing field branches. In this way, the absence of a hysteresis loop in G3 and G4 of homometallic samples could be due mainly to the absence of metallic iron as confirmed by XRD results (Table 1). In addition, magnetic properties of the iron phosphides observed in homometallic particles are significantly different according to their stoichiometry and structure. Thus, the FeP orthorhombic phase exhibits antiferromagnetic properties below 115 K, whereas the tetragonal (hexagonal) crystal structures of Fe 3 P (Fe 2 P) phase shows ferromagnetic temperature above (below) RT [46,47]. So, it is reasonable to assume that the absence of both Fe and Fe 3 P phases could be contributed to the lack of the hysteresis loop on the former samples.

Magnetic Properties
An initial examination of the magnetic properties of particles using a mag stir bar indicated some kind of inducted magnetism because the samples we tracted to the magnetic bar. To further understand their magnetic propertie EV9 Microsense Vibrating Sample Magnetometer (VSM) was used to get the magn tion curve (Figure 7), which depicts the magnetization vs. applied magnetic field measured at room temperature (RT) for homometallic (top) and heterometallic (bo materials. Except for G3 and G4 on homometallic samples, the rest of the samples e a typical hysteresis loop characteristic of ferromagnetic substances, which separa creasing and decreasing field branches. In this way, the absence of a hysteresis loop and G4 of homometallic samples could be due mainly to the absence of metallic ir confirmed by XRD results (Table 1). In addition, magnetic properties of the iron phides observed in homometallic particles are significantly different according to stoichiometry and structure. Thus, the FeP orthorhombic phase exhibits antiferroma properties below 115 K, whereas the tetragonal (hexagonal) crystal structures of (Fe2P) phase shows ferromagnetic temperature above (below) RT [46,47]. So, it is re able to assume that the absence of both Fe and Fe3P phases could be contributed lack of the hysteresis loop on the former samples.  The remanent magnetization (Mr) and coercive field (Hc) of these ferromagnetic complexes are directly determined in M(H) curves from the magnetization and field axis crossing points, respectively, whereas the saturation magnetization (Ms) is estimated through the maximum magnetization value reached (Tables 3 and 4).  The remanent magnetization (M r ) and coercive field (H c ) of these ferromagnetic complexes are directly determined in M(H) curves from the magnetization and field axis crossing points, respectively, whereas the saturation magnetization (M s ) is estimated through the maximum magnetization value reached (Tables 3 and 4). Concerning this ferromagnetic parameter, saturation magnetization values seem to be correlated with the metallic amount present in each sample. Since the heterometallic particles have more metallic phases than homometallic particles, this parameter reaches higher values than the ferromagnetic homometallic ones and ultimately levels off saturation magnetization (M s ) of 60-75 emu/g are reached on this group. Besides that, the homometallic particles showed dendritic effects on ferromagnetic parameters, particularly H c and M s , which decreased with increased generations [41]. Moreover, the magnetic properties of nanoparticles are governed by various parameters, including concentration and interparticle distance [48][49][50][51]. Thus, it has been previously shown that as the concentration of magnetic species increases to a critical point, the distance between particles decreases, which leads to an increase in dipolar interaction and eventually an increase in H c [51][52][53]. Therefore, it is logical to presume that changes in iron concentration in the homometallic samples regulated H c and M s , leading to the observed trend. In contrast to the homometallic particles, no structure-property relationship was observed within the heterometallic ones.
On the other hand, Figure 8 shows the temperature dependence of magnetization, M(T) curves, under an applied magnetic field of 1 kOe. The M(T) curves for homometallic samples exhibit an offset in their magnetization at temperatures around to 200 K, a step which seems to be correlated with Fe 2 P percentages (Table 1). Moreover, the iron phosphide (2/1) Curie temperature of 209 K could be slightly altered by means of stoichiometry, interparticle interaction, morphology or structure [48]. In this sense, orthorhombic cobalt phosphides (2/1) were not ferromagnetic, in contrast with the hexagonal iron phosphide (2/1). Nevertheless, the latter phase is isostructural to the beta-form of the cobalt phosphide (2/1) so a possible doping of iron in this form could be on the slope change observed on M(T) curves for the heterometallic samples with β-Co 2 P content (i.e.,: Hetero-G1 and G2). Finally, it is clear in the figure that the larger cobalt-iron nanoclusters in heterometallic samples have helped to enhance their magnetization susceptibility significantly and also stabilize the magnetization temperature dependence compared with homometallic samples.

Materials and Instrumentation
All used chemicals and reagents were purchased from Sigma-Aldrich and utilized as received. The solvents were dried and stored over 3 Å molecular sieves before being used. The designs of the organoiron complex 1 and dendrimer G1-D1 were achieved by following previously reported procedures [54][55][56]. Morphological characterizations, PXRD

Materials and Instrumentation
All used chemicals and reagents were purchased from Sigma-Aldrich and utilized as received. The solvents were dried and stored over 3 Å molecular sieves before being used. The designs of the organoiron complex 1 and dendrimer G1-D1 were achieved by following previously reported procedures [54][55][56]. Morphological characterizations, PXRD diffraction, and magnetic properties studies were performed at the University of Oviedo-CINN, Spain.

Instrumentation
All NMR spectra of synthesized dendrimers were recorded using a Bruker Avance NMR Spectrometer ( 1 H, 300 MHz and 13 C, 75 MHz). The spectra were obtained from a DMSO-d6 solution of the complexes with the chemical signals referenced to the solvent residual signal in ppm. Attenuated total reflection Fourier-transform IR (ATR-FTIR) spectroscopic measurements were achieved on a Bruker Alpha FTIR spectrometer Alpha-P using KBr pellet technique in the wavenumber range between 4000 to 400 cm −1 . Elemental carbon and hydrogen analyses for prepared dendrimers were performed on CE-440 Elemental Analyser, Exeter Analytical. Thermogravimetric analysis (TGA) was conducted in platinum pans under nitrogen at a heating rate of 10 • C on a TA Instruments TGA Q500.

Morphological Characterization
SEM micrographs and X-ray microanalysis (SEM/EDX) were recorded using a JEOL-6610 LV scanning electron microscope operating at 30 kV coupled with an Oxford X-Max microanalysis system (EDX). TEM and BF-STEM images, SAED patterns, and BF-STEM/EDX were recorded on a JEOL JEM-2100F field emission transmission electron microscope, at 200 kV, equipped with a STEM unit and an Oxford X-Max microanalysis system (EDX).

X-ray Diffraction
The X-ray diffraction (XRD) patterns for magnetic materials were measured on a Seifert XRD 3000 TT diffractometer operating in Bragg-Brentano geometry. Measurements were done using MoK α radiation (0.7107 Å), where the primary incident, secondary antiscatter slits of 2 mm and a primary mask were used to illuminate the powder samples compacted in a 30 mm square plastic holder. Vertical Soller slits were also used after the incident and anti-scatter slits to delimit the axial divergence. A secondary high-orientated pyrolytic graphite (HOPG) monochromator and 0.2 mm receiving slit were placed before the scintillation detector. XRD patterns were collected between 7 • and 38 • 2θ range in step mode, recording diffracted intensity every 0.02 • with 20 s counting time for each point.

Magnetometry
Room temperature (RT) magnetization curves, M(H), were measured in a EV9 Microsense Vibrating Sample Magnetometer (VSM) within an applied magnetic field range of ±20 kOe. Besides that, VSM is equipped with EV1-LNA temperature control option, which allows us to establish the temperature dependence of magnetization, M(T) curve, under 1 kOe applied magnetic field in a 10 K/min heating rate from 100 to 300 K. In order to perform both measurements, about 100 mg of each complex were encapsulated into a 70 mm 3 acrylic cup which is firmly stuck to an 8 mm Pyrex transverse rod by means double side Scotch ® and PTFE tapes.

General Procedure
Five generations of dendrimers were synthesized in a good yield (73-87%). Incorporating the triple bond throughout dendrimer branches was achieved by reacting the carboxylic group in complex 1 with the hydroxyl group in the compound a in the presence of DMAP and DCC to give complex 2, which is based on nucleophilic aromatic substitution reaction (S N Ar) with G1-D1 in the presence of the weak base, K 2 CO 3 produced G2-D3. The synthesis of the five generations of homometallic dendrimers involved a well-established nucleophilic aromatic substitution reaction (S N Ar) and an esterification reaction. For instance, the synthesis of homometallic dendrimers G1-D2, G2-D4, G3-D6, and G4-D8, involved nucleophilic substitution reaction of homometallic dendrimers G1-D1, G2-D3, G3-D5, G4-D7 with 5-(4-hydroxyphenyl)-pentanoic acid utilizing 1:6, 1:12, 1:24, and 1:48 molar ratios. The reactant mixtures were stirred in DMF with the presence of K 2 CO 3 at 55 • C for 24 h after flushing with nitrogen for 30 min. Consequently, the mixtures were then poured into a 10% HCl solution, and NH 4 PF 6 was added to get the final products.
The Steglich esterification procedure was used to synthesize dendrimers G2-D3, G3-D5, G4-D7, and G5-D9 via reacting dendrimers G1-D2, G2-D4, G3-D6, G4-D8 with complex 2 using appropriate molar ratios. First, the reaction mixtures were stirred at 0 • C for 10 min. After that, the mixtures were stirred at room temperature under nitrogen for 15 min before being left to stir for another two days at room temperature. Purification was achieved by maintaining the mixture at −25 • C for two hours, filtered to remove the remaining DHU, and the removal of the solvent gave rise to the products. Detailed synthetic methodologies, yields %, and characterization using 1 H and 13 C NMR, ATR-FTIR, and elemental analyses data are reported here.

Synthesis of Complex 2, from 2-Butyne-1,4-Diol (a) with Complex 1
Steglich esterification was used to react the carboxylic group in complex 1 with the hydroxyl group in the 2-butyne-1.4-diol to synthesize complex 2 [57]. In 25 mL roundbottom flask was added complex 1 (0.    3.3.11. Heterometallic Dendrimer Co/Fe-dendrimerd3 (HETERODEN 1) The heterometallic dendrimer was synthesized using a previously reported method [42,58]. Under the N 2 atmosphere, homometallic dendrimer G2-D3 (0.25 g, 0.023 mmol) was dissolved in 1 mL of dried DMF and 10 mL of dried THF. Co 2 (CO) 8 was added upon complete dissolution, and then the reaction mixture was stirred at room temperature inside the glovebox for 72 h. Subsequently, the THF was evaporated using rotary evaporation, and the red residue was dissolved into 100 mL acetone. After 10 min, the brown precipitate formed was filtered and reprecipitated into 10-fold excess of diethyl ether. This technique was used three times to obtain the final product in 72% yield as a brown solid (Molecular weight 12,387.04 g/mol

Formation of Magnetic Materials Containing TMPs Phases
The magnetic materials containing mixture phases of TMPs was prepared using a previously described technique [30]. The dendrimer sample was weighed into a quartz boat, transferred inside a quartz tube connected to ultrapure nitrogen gas, and placed in a pyrolysis furnace. The furnace temperature was gradually raised to 900 • C over 3 h and then held constant for 4 h in a nitrogen stream. After the furnace was cooled to room temperature under a nitrogen flow (typically over a period of 3 h), the black particles were collected and weighed.

Conclusions
Magnetic materials have attracted many researchers due to their significance in several advanced applications. Here, we designed five generations of homometallic and four generations of heterometallic dendrimers, which upon pyrolysis, yielded room temperature ferromagnetic materials containing separate iron and cobalt phosphide phases. Powder-XRD, SEM and TEM, as well as SAED, revealed that the homometallic samples were a polycrystalline nature of the nearly aggregated particles and reflected single-crystalline diffraction for heterometallic magnetic ones. Dendritic effects on ferromagnetism at RT were observed with homometallic samples where H c and M s decreased with increasing precursor generation. Incorporating cobalt nanoclusters in heterometallic samples has helped to enhance their magnetization susceptibility at RT significantly compared to homometallic samples. The data gained further shows that the magnetism of the heterometallic particles was less susceptible to the influence of temperature below RT than homometallic particles, which exhibit magnetic phase transitions at temperatures around 200 K that seems to be correlated with the presence of hexagonal structures of iron/cobalt phosphides (2/1). Therefore, the dendrimer structures can be considered an important platform for the synthesis of precursors for magnetic materials containing a mixture of TMP phases, as it allows functionalization with multiple ferromagnetic metals and the control of the magnetism through dendritic effects.
Supplementary Materials: The following are available online, Table S1: Refined lattice parameters for crystalline phases identified on XRD patterns of magnetic homometallic samples [59][60][61][62][63][64][65], Table S2: Refined lattice parameters for crystalline phases identified on XRD patterns of magnetic heterometallic samples, Table S3: Show Crystal size in Å and Crystallinity of magnetic homometallic samples, Table S4: Show Crystal size in Å and Crystallinity of magnetic heterometallic samples, Figure S1: Whole pattern profile fit for the X-ray diffraction pattern of: (a) HOMO-G1, (b) HOMO-G2, (c) HOMO-G3 and (d) HOMO-G4 by means Rietveld method: observed (red points) and calculated (black line). Positions of the Bragg reflections are depicted by green vertical bars (arranged in rows for each phase) and the observed-calculated difference is showed by blue line at the bottom, Figure S2 Funding: The authors acknowledge the Libyan Ministry of Education for financial support and thank funding from the UPEI Doctoral Research Support Program. We also acknowledge the financial support from Spanish Ministerio de Economía y Competitividad (PID2020-113558RB-C41) and Gobiernodel Principado de Asturias (GRUPIN-ID2018-170).

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The data presented in this study are available in supplementary material.