Supporting Information Experimental Procedure Reactions were carried out using standard Schlenk techniques. Tri-n-octylamine (TOA; 98%), oleic acid (OA; 90%), ethanol, toluene, tetrahydrofuran, and hexane were obtained from Sigma-Aldrich. TOA and OA were dried separately before use by heating to ~110 oC under vacuum. All other solvents were distilled using standard procedures.1 Fe3(CO)12, t-butyl dichlorophosphine, and lithium aluminum hydride were obtained from Strem and used as received. The precursor, H2Fe3(CO)9PtBu, was prepared from Fe3(CO)12 and tBuPH2 in refluxing toluene, as previously reported.2 Tert-butyl phosphine was synthesized via the reduction of tBuPCl2 with LiAlH4. Characterization. Fourier Transform-Infrared (FTIR) spectra were collected with a Thermo-Nicolet 670 FT-IR using a 0.1 mm CaF2 cell. Scanning Electron Microscopy was performed using a FEI XL-30 Environmental Scanning Electron Microscope (ESEM). Transmission electron microscopy (TEM) experiments were performed by depositing a drop of a suspension diluted in hexane on a carbon-coated copper grid. The solvent was evaporated and the sample was analyzed using using JEOL 2000FX and JEOL 2010 microscopes that were equipped with energy-dispersive spectrometers and operated at 200 kV and 100 kV, respectively. Conventional and high-resolution TEM imaging, selected area electron diffraction (SAED) and energy-dispersive spectroscopy (EDS) methods have been used for analysis of the iron phosphide nanoparticles.
X-ray diffraction (XRD) data were obtained with a powder
diffractometer (Rigaku D/Max-2100PC) using unfiltered Cu Kα radiation (λ = 1.5406 Å) at 40 kV and 40 mA. The contribution from Kα2 radiation was removed using the Rachinger algorithm. Goniometer alignment was verified by daily analysis of a Rigaku-supplied SiO2 reference standard. Elemental analyses were obtained from Galbraith Analytical Laboratories. SQUID magnetization measurements were performed on a Super Quantum magnetometer (MPMS 5.5, equipped with a Squid detector). The temperature was varied between 2 and 300 K according to a classical zero-field cooling/field cooling
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(ZFC/FC) procedure in the presence of a very weak applied magnetic field (1000 Oe), and the hysteresis cycles were obtained at different temperatures in a magnetic field varying from +50 to -50 kOe. Synthesis of Iron Phosphide Nanofibers (1).
Iron phosphide nanofibers were synthesized by
decomposing 0.5 mmol H2Fe3(CO)9PtBu in the presence of TOA (7 mL) and OA (1 mL). This deep red solution was heated to 315 oC with a standard heating mantle and magnetic stirring, at which time the solution turned black (the exact temperature at which the solution turned black varied, depending on the ratios of surfactant, from 315 to 330 oC). The mixture was stirred for an additional 20 minutes at that temperature. After cooling to room temperature, the nanoparticles were precipitated with ethanol. The supernatant was removed, and the remaining black solid was washed several times with hexane. Synthesis of Nanofiber “Bundles” (2). Keeping all conditions as in (1), but varying the ratio of TOA to OA (6 mL:2 mL, 4 mL:4 mL, etc.) resulted in “bundles” of nanofibers. Synthesis of Dumbbell-Shaped Nanofiber “Bundles” (3). Using the same conditions as in (1), but adding small amounts of hexane or other alkanes (i.e. nonane or tridecane) before heating the solution, dumbbell-shaped bundles of nanofibers were formed. Following Decomposition using FT-IR. In order to determine how the precursor decomposed, the reaction was monitored by FT-IR. Small portions of the solution were taken from the mixture at various intervals (100 oC, 125 oC, 135 oC, and 140 oC) and diluted in hexane. An IR spectrum was also taken in which the precursor was dissolved in hexane for comparison to the literature values. Additionally, in order to determine the effect that the TOA had on the precursor, a few drops of TOA were added to a solution of the precursor in THF.
2
Intensity
Fe2P, Barringerite
20
30
40
50
60
70
2 Theta (degrees)
Figure S1. X-Ray Powder Diffraction Pattern for the iron phosphide nanorods. Peaks correspond to PDF 51-0943 (Fe2P). Infrared support of the suggested decomposition mechanism. Table S1 gives the experimentally obtained carbonyl frequencies along with the values reported in the literature. H2Fe3(CO)9PtBu Literature2 hexane 2081 m 2058 s 2032 vs 2008 s 1985 m 1973 w
Table S1.
Experimenta l hexane 2092 m 2057 s 2030 vs 2005 s 1986 m 1973 w
H2Fe3(CO)9PtBu+TOAÆ HFe3(CO)9PtBuLiterature3 Experimental
HFe3(CO)9PtBu- Æ Fe4(CO)12(PtBu)2 Literature4 Experimental
a
THF 2037 m 1991 vs 1963 s 1951 s 1929 m 1896 w
THF 2038 m 1993 vs 1967 vs 1954 s 1931 m 1898 w
b
cyclohexane 2033 vs 2020 s 1993 s 1979 m
hexane 2034 vs 2016 vs 1994 s 1979 m
IR values (Literature & Experimental Values) of the clusters present during the
decomposition (w: weak, m: medium, s: strong, vs: very strong). added a few drops of TOA.
b
a
Precursor dissolved in THF, then
IR taken during the monitoring of the decomposition; reaction mixture at
140 oC.
3
2005
94
2057
%Transmittance
96
92
A
1986
2092
98
1973
100
90 88
2200
2030
86
2100
2000
1900
Wavenumbers (cm-1)
2038
96 94
B
92 90
1954
%Transmittance
1931
98
1898
100
88 86
1993
84
1967
82 80 78 2200
2100
2000
1900
Wavenumbers (cm-1)
82
C 2056
1950
78
1993 1986 1976
%Transmittance
80
76
74
70 68 2200
2100
2016
2035
72
2000
1900
Wavenumbers (cm-1)
Figure S2. IR spectra. A) IR of H2Fe3(CO)9PtBu in hexane at room temperature. B) IR of a solution of H2Fe3(CO)9PtBu in THF with a few drops of TOA added. C) IR of an aliquot of the decomposition reaction taken at 140 oC; diluted in hexane. 4
hkl (110) (001) (110) (101) (200) (111) (201) (210) (002) (300)
Measured d-spacing (Å) 4.98 3.46 3.01 2.85 2.55 2.26 2.07 1.93 1.75 1.69
Intensity vw b vw vvw vw w vs s m m m
Fe2P d-spacing (Å) 5.09 3.44 2.94 2.85 2.55 2.23 2.05 1.92 1.72 1.70
a
Figure S3. d-spacings from the Polycrystalline Selected Area Electron Diffraction (SAED) pattern of the nanorods compared to published values. More discrepancies are seen in the weaker reflections due to the fact that measurements taken from TEM data are not as precise as those from X-ray diffraction data.
a
JCPDS card file 33-670.
b
vvw: very very weak, vw: very weak, w: weak, m: medium, s:
strong, vs: very strong.
Figure S4. TEM image of a T-shaped bundle.
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Figure S5. SEM image of iron phosphide nanorods synthesized with the addition of 100 μL hexane.
Figure S6. TEM image of a cross-shaped bundle.
Figure S7. TEM image of a T-shaped bundle obtained from a decomposition with 4 mL TOA, 4 mL OA, and 100 μL nonane.
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A
B
C Figure S8. A schematic representation of the Fe2P crystal structure looking down the c axis.5 The red atoms are iron and the lilac atoms are phosphorous. The atom coordinates are Fe(1): 0.255, 0, 0; P(1): 0.33333, 0.66667, 0; Fe(2): 0.596, 0, 0.5; P(2): 0, 0, 0.5. The structure can be viewed as being built of alternating layers as shown for (A) The z = 0 layers, and (B) The z = 0.5 layers. (C) shows the combination of one z = 0 and one z = 0.5 layer. The unit cell is outlined with dotted lines. The iron atoms in the z = 0 layers are tetrahedral, while those in the z = 0.5 layer are square pyramidal. The square pyramidal iron atoms have four bonds to P of 2.485 and one of 2.371 Å, while the tetrahedral iron atoms have two bonds to P of 2.222 and two of 2.287 Å. The iron atoms in the z = 0.5 layer connect to two P atoms in the z = 0 layer above and below to generate the square pyramidal geometry, while the iron atoms in the z = 0 layer bond to one phosphorus atom in the z = 0.5 layer above and one below to generate a tetrahedral configuration.
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Figure S9. TEM image of a one-minute reaction, solvent system TOA:OA 4:4.
Figure S10. Hysteresis loops of the iron phosphide nanorods with bundle-morphology (B).
References (1) Perrin, D. D.; Armarego, W. L. Purification of Laboratory Chemicals; 5th ed.; Pergamon Press: New York, 1993. (2) Huttner, G.; Schneider, J.; Mohr, G.; Von Seyerl, J. J. Organomet. Chem. 1980, 191, 161-169. (3) Knoll, K.; Huttner, G.; Zsolnai, L.; Orama, O.; Wasiucionek, M. J. Organomet. Chem. 1986, 310, 225-247. (4) Vahrenkamp, H.; Wolters, D. J. Organomet. Chem. 1982, 224, C17-C20. (5) Fujii, H.; Uwatoko, Y.; Motoya, K.; Ito, Y.; Okamoto, T. J. Phys. Soc. Jpn. 1988, 57, 21432153.
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