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Synthesis and molecular structures of cobalt(II) β-diketonate complexes as new MOCVD precursors for cobalt oxide films
Polyhedron 23 (2004) 735–741 www.elsevier.com/locate/poly
Synthesis and molecular structures of cobalt(II) b-diketonate complexes as new MOCVD precursors for cobalt oxide films Sergej Pasko
a,b
, Liliane G. Hubert-Pfalzgraf a,*, Adulfas Abrutis Jacqueline Vaissermann c
b,*
,
a Universite Lyon 1, IRC-CNRS, 2 av. A. Einstein, 69626 Villeurbanne cedex, France Department of Chemistry, Vilnius University, Naugarduko 24, LT2006 Vilnius, Lithuania Laboratoire de Chimie des Metaux de transition, UMR-CNRS, 4 place Jussieu, Paris, France b
c
Received 17 September 2003; accepted 18 October 2003
Abstract Adducts of cobalt(II) 2,4-pentanedionate (acac) and 2,2,6,6-tetramethyl-3,5-heptanedionate (thd) with TMEDA (N ; N ; N 0 ; N 0 tetramethyl-1,2-diaminoethane) and aminoalcohols, namely 1-dimethylamino-2-propanol (DMAPH) and 2-dimethylaminoethanol (DMAEH), have been synthesized and characterized by elemental analyses, FT-IR, 1 H NMR, mass spectrometry and TGA. The molecular structures of Co(acac)2 (TMEDA) (1) and [Co(acac)2 (DMAPH)]2 (2) have been determined by single-crystal X-ray dif av.). The most fraction. 1 is monomeric while 2 is dimeric with two molecules linked by hydrogen bonds (O–H–O distance 2.708 A volatile and stable new adducts Co(acac)2 (TMEDA) and Co(thd)2 (TMEDA) have been studied as precursors for cobalt oxide deposition by liquid injection MOCVD in DME on monocrystalline LaAlO3 and Si substrates. Films were characterized by XRD and XPS. These preliminary MOCVD experiments showed that epitaxial Co3 O4 films can be obtained by using both new precursors. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Cobalt; Oxide; b-diketonates; Adducts; Structures; MOCVDf
1. Introduction Cobalt oxides are of great interest due to useful properties, such as high catalytic activity at low cost [1], antiferromagnetism [1], electrochromism [2]. Cobalt oxide films have been considered for uses as magnetic detectors, membranes for oxidation of hydrocarbons, counter electrodes, humidity or oxygen optical sensors [3,4], solar-selective absorbers and protective layers [1,5,6]. Cobalt oxide films have been deposited by a variety of methods including conventional MOCVD [1,2,5–8]. However, despite the interest of MOCVD of Co3 O4 , reports are scarce. [Co(acac)2 ]4 was generally used as a precursor [1,5,7,8], although the use of Co(acac)3 [8], Co(OAc)2 [9] and more recently of *
Corresponding authors. Tel.: +37052331004; fax: +37052330987. E-mail address: [email protected] (A. Abrutis).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2003.11.044
Co(thd)2 [10] or Co(NO3 )3 [11] has been reported. Another use of cobalt b-diketonates is for the CVD of Co films [12]. A number of cobalt(II) acetylacetonate adducts with N-donors have been described [13–18]. Although some of them such as Co(acac)2 (LL) [LL ¼ 2,20 -bipyridyl (130 °C/102 Torr), 1,10-phenantroline (190 °C/102 Torr)] [19] and Co2 (acac)4 (piperidine) (80 °C/104 Torr) [20] were volatile, no adduct was used so far for MOCVD applications. Cobalt b-diketonate adducts are also good catalysts for a number of reactions, such as polymerisation, enantioselective Michael addition, etc. [21–23]. We report here the synthesis and structural characterization of some new adducts of cobalt(II) 2,4-pentanedionate and 2,2,6,6-tetramethylheptane-3,5-dionate and the preliminary study of the most volatile and stable new adducts as precursors for the deposition of cobalt oxide films by liquid injection MOCVD.
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2. Experimental 2.1. Syntheses Syntheses of air-sensitive complexes were performed under argon using Schlenk tubes and vacuum line techniques. Solvents were purified by standard methods. TMEDA (N ; N ; N 0 ; N 0 -tetramethylethylenediamine), DMAEH (2-dimethylaminoethanol), DMAPH (1-dimethylamino-2-propanol), thdH (2,2,6,6-tetramethyl-3, 5-heptanedione) and acacH (acetylacetone, 2,4-pentanedione) were distilled and stored over molecular sieves. Co(thd)2 and Co(acac)2 (H2 O)2 were prepared as reported [10,24]. [Co(acac)2 ]4 was obtained by sublimation of Co(acac)2 (H2 O)2 at 100–120 °C/2 104 Torr (67%). It is slightly hygroscopic. FT-IR spectra were recorded with a Perkin–Elmer Paragon 500 Spectrometer as Nujol mulls. Mass spectra were obtained using a Thermofinnigan Mat95XL spectrometer under standard electron ionization conditions (E1 ¼ 70 eV). TGA experiments were performed under air with a Setaram 62 system using a thermal ramp of 10 °C/min. Proton NMR spectra were recorded in the range )130 to +130 ppm using the solvent peak as a reference on an AM250 Bruker spectrometer. Elemental analyses were done at the Centre de microanalyses du CNRS and at Vilnius University. Co(acac)2 (TMEDA) (1) was previously reported [15], it was prepared by a modified procedure. TMEDA (10% excess) was added to Co(acac)2 (H2 O)2 , the reaction medium was evaporated after 2 h and sublimed at 70 °C/2 104 Torr (90%). MS (m=zþ , %): M (5), M-acac (26), M-TMEDA (43), M-CH3 -TMEDA (76), M-acac-TMEDA (84), M-acac-CH3 -TMEDA (7), TMEDA (7), acacH (4), Me2 N@CH2 (100). 1 H NMR (CDCl3 , 20 °C): )13.19 broad (Me(acac) + CH, 8H), 10.51 s (6H, Me acac), 38.69 s (2H, CH2 ), 47 s (6H, Me2 N), 67 s (2H, CH2 ), 78.08 s (6H, Me2 N). [Co(acac)2 (DMAPH)]2 (2). 0.70 g (0.68 mmol) of [Co(acac)2 ]4 were dissolved in 20 ml of toluene and 0.37 ml (3.02 mmol) of DMAPH were added. The color of the solution changed from dark violet to red. After stirring for 2 h and concentration, 2 crystallized at )30 °C (0.72 g, 73%). Anal. Calc. for C15 H27 CoNO5 : C, 50.00; H, 7.55, N, 3.89. Found: C, 49.50; H, 7.49, N, 3.85%. IR, cm1 : 3390 w (mOH); 1599 vs, 1519 vs (mC@O, mC@C); 558 m, 505 w (mCo–O, mCo–N). 1 H NMR (CDCl3 , 20 °C): )14.52 s (2H, CH), 12.28 broad [15H, Me(acac) + Me(CH)], 32.85 broad (8H, Me2 N + CH2 ), 71.93 s (1H, CHO). [Co(acac)2 (DMAEH)] (3). 0.88 g (0.85 mmol) of [Co(acac)2 ]4 were dissolved in 25 ml of toluene. Addition of 0.38 ml (3.75 mmol) of DMAEH gave a red precipitate which was filtered after 16 h. A second crop of 3 was obtained by concentration at )30 °C (0.74 g, 72%). Anal. Calc. for C14 H25 CoNO5 : C, 48.56; H, 7.28;
N, 4.04. Found: C, 48.00; H, 7.30; N, 3.92%. IR, cm1 : 3109 w (mOH); 1595 vs, 1520 vs (mC@O, mC@C); 554 w (mCo–O, mCo–N). 1 H NMR (CDCl3 , 20 °C): )14.10 s (2H, CH), 12.13 s (12H, Me, acac), 32.85 broad (Me2 N + CH2 , 8H), 71.93 s (2H, CH2 O). Co(thd)2 (TMEDA) (4). Same procedure as for 2 applied to 0.32 g (0.75 mmol) of Co(thd)2 in 10 ml of toluene and 0.12 ml (0.83 mmol) of TMEDA. The reaction mixture was evaporated after 2 h and sublimed at 125 °C/2.3 102 Torr (80%). Anal. Calc. for C28 H54 CoO4 N2 : C, 62.09; H, 10.05, N, 5.17. Found: C, 62.73; H, 10.16, N, 5.40%. IR, cm1 : 1594 vs, 1582 vs, 1570 vs; 1531 s, 1504 vs (mC@O, mC@C); 609 w, 586 w, 478 m (mCo–O, mCo–N). MS (m=zþ , %): M (19), M-TMEDA (35), M-t Bu-TMEDA (100), M-C11 H19 O2 (10), MC11 H19 O2 -TMEDA (15). thdH (2.8), t BuCOCH2 CO (15), TMEDA (10). 1 H NMR (CDCl3 , 20 °C): )17.53 s (2H, CH), )5.09 s (18H, t Bu), 8.06 s (4H, Me2 N), 32.24 (18H, t Bu), 46.80 (2H, CH2 ), 67.82 (2H, CH2 ), 78.87 (12H, Me2 N). All compounds were soluble in usual organic solvents, except for 2 and 3, insoluble in aliphatic hydrocarbons. Solubility was generally lower in polar solvents (N ; N -dimethylformamide, CH3 CN, alcohols). All complexes but 1 are slightly air-sensitive, their colour changed to green on storage for over six months in air, oxidation to Co(III) was faster in solutions especially polar ones. 2.2. Crystallography of 1 and 2 Crystals of 1 and 2 were obtained by sublimation at 80–85 °C/2.3 102 Torr and by recrystallisation in toluene at )20 °C, respectively. Data were collected with an Enraf–Nonius MACH3 diffractometer. Unit cell dimensions with estimated standard deviations were obtained from least squares refinements of the setting angles of 25 well-centred reflections. Corrections were made for Lorentz and polarization effects. Empirical absorption correction (Difabs) was applied. Crystallographic data and other pertinent information are summarized in Table 1. Computations were performed using C R Y S T A L S [25]. Atomic form factors for neutral Co, O, N and C were taken from [26]. Anomalous dispersion was taken in account. All atoms were anisotropically refined. Hydrogen atoms were introduced in calculated positions. Least-squares refinements (full matrix) were carried out by minimizing the function P wðjFo j jFc jÞ2 , where Fo and Fc are the observed and calculated structure P factors. Models P reached converP gence with RP ¼ ðjjFo j jFc jjÞ= jFo j and Rw ¼ ½ ðjFo j jFc jÞ2 = wðFo Þ2 1=2 having values listed in Table 1. A weighting scheme [27] was applied. Criteria for a satisfactory complete analysis were the ratios of rms shift to standard deviation being less than 0.1 and no significant features in the final map.
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Table 1 Crystal data for Co(acac)2 (TMEDA) and [Co(acac)2 (DMAPH)]2 Formula Formula weight a (A) b (A) c (A) a (°) b (°) c (°) 3 ) V (A Z Crystal system Space group Linear absorption coefficient l (cm1 ) Density q (g cm3 ) Radiation h Limits (°) Temperature of measurement (K) Number of data collected Number of unique data collected Number P of unique data P used for refinement (on F ) R ¼ h kFo j jFc k= jFo j i1=2 P P wðjFo j jFc jÞ2 = wFo2 Rw ¼ Extinction parameter Number of variables 3 ) Largest difference peak and hole (e A
C16 H30 CoN2 O4 (1) 373.36 8.500(4) 10.193(3) 11.565(6) 90 92.35(4) 90 1001.0(7) 2 monoclinic Pn 8.71 1.24 Mo Ka (k ¼ 0:71069 A) 1–28 295 2720 2422 (Rint ¼ 0:03) 1764 ðFo Þ2 > 3rðFo Þ2 0.0476
C15 H27 CoNO5 (2) 360.3 10.674(2) 12.083(1) 14.452(2) 93.11(1) 91.96(2) 92.01(1) 1858.8 4 triclinic P 1 9.39 1.29 Mo Ka (k ¼ 0:71069 A) 1–26 251 7700 7288 (Rint ¼ 0:01) 4884 ðFo Þ2 > 3rðFo Þ2 0.0399
0.0525 691 210 0.40
0.0496 122 398 0.50
2.3. CVD experiments and films characterisation
3. Results and discussion
Deposition of Co3 O4 films was carried out by innovative pulsed liquid injection MOCVD (PI-MOCVD) [28]. Detailed description of this technique and of the reactor is given elsewhere [29,30]. Solutions (0.05 M) of precursors in 1,2-dimethoxyethane (monoglyme) were used for the depositions (injection frequency 2 Hz, microdose mass 4 mg). The carrier gas was a mixture of Ar (54 l/h) and O2 (36 l/h). Depositions were performed on monocrystalline LaAlO3 (1 0 0) and Si(1 0 0) substrates under 5 Torr total pressure. Substrates were cleaned in boiling toluene and its vapour before use. After deposition, films were cooled down to RT in an O2 atmosphere (1 atm). Films crystallization and texture were studied by Xray diffraction (XRD) with a Siemens D500 diffractometer (Cu Ka radiation). The film in-plane orientation was studied by XRD in Schultz geometry. X-ray photoelectron spectroscopy (XPS, VG ESCALAB 200R, Al Ka radiation) was also used. The in-depth film purity was evaluated after Arþ sputtering at 4 keV, 3.75 107 Torr argon pressure. A non-linear least-squares program (Eclipse V2.0) adopting Gaussian–Lorentzian peak shapes was used for the raw spectra fitting and for the evaluation of atomic compositions. Thickness of the films on Si(1 0 0) substrates was determined by profilometry (Taylor–Hobson) on a step formed by lithography. The thickness value was used for the calculation of the film growth rate.
3.1. Synthesis and characterization Adducts of cobalt(II) acetylacetonate with TMEDA, DMAEH and DMAPH were easily obtained either by ligand exchange reaction from Co(acac)2 (H2 O)2 or by decomplexation of [Co(acac)2 ]4 at RT. It is noticeable that the decomplexation of [Co(acac)2 ]4 by aminoalcohols was more effective than that of [Ni(acac)2 ]3 [31]. [Co(acac)2 ]4 by contrast did not react with O-donors such as DME, triglyme and tetraglyme even in refluxing toluene for 24 h. These observations account for the absence of decomplexation and/or ligand exchange reactions in DME solutions, the solvent used for the CVD experiments. Co(thd)2 and Co(thd)2 (TMEDA), the first adduct of Co(thd)2 reported, are also stable in DME. The complexes were characterized by elemental analyses, FT-IR, 1 H NMR, mass spectrometry and TGA. Their FT-IR spectra display the mC@O and mC@C absorption bands of the b-diketonate ligands in the 1504–1600 cm1 range as well as those of the Lewis base. The spectra of 2 and 3, the complexes with aminoalcohols, showed also absorptions at 3390 and 3109 cm1 , respectively, due to mOH stretching. Their frequency is lower than that of the corresponding free alcohol – 3433 and 3385 cm1 – respectively suggesting thus coordination. All compounds were volatile, the order of their sublimation rate under vacuum in identical conditions was as follows: Co(acac) 2 (TMEDA) >
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Co(thd)2 > Co(thd)2 (TMEDA) > [Co(acac)2 ]4 > [Co(aca c)2 (DMAPH)]2 [Co(acac)2 (DMAEH)]2 . The two latter adducts sublimed at 80 and 90 °C/104 Torr, respectively, but with partial loss of the aminoalcohol ligand especially for 3, the DMAEH adduct. Due to this behaviour, adducts 2 and 3 were not investigated as MOCVD precursors for cobalt oxide films. The complexes with TMEDA were totally recovered as adducts by sublimation under vacuum thus reflecting the higher thermal stability of the N,N-donor Co b-diketonate adducts as compared to those with the O,N-donors. The volatility of the tetramethylheptanedionate derivatives, is, as expected higher than that of the acetylacetonate ones except 1 [32]. TGA-DTA analyses were performed in air. Fig. 1 illustrates the data for 1. The amount of residue of black Co3 O4 (18.3%), lower than the theoretical amount (21.5%) and the almost horizontal DTA curve part show that 1 sublimed partially (15%) in the 130–230 °C temperature range. Subsequent events are the loss of TMEDA and acacH which occurred at temperatures lower than 260 °C and the oxidation of the residue as evidenced by the strong exothermic peak at 370 °C. The mass spectra of Co(acac)2 (TMEDA) (1) and of Co(thd)2 (TMEDA) (4) show the molecular ions, the stability being in the favour of 4. The main decomposition pathways of the molecular ions are the loss of TMEDA then of the methyl groups and acac for 1, of both TMEDA and butyl groups for 4. These patterns are in agreement with the literature. [10]. A peak at m=z ¼ 608 (25%) attributed to Co(thd)3 was observed for samples of 4 stored in air for 6 months. The oxidation rate to Co(III) species by air was 1 < 4 < 2 < [Co (acac)2 ]4 < Co(thd)2 < 3 according to 1 H NMR data. Thus, an advantage of the Co(II)-TMEDA adducts 1 and 4 by comparison to ligand free Co(II) b-diketonates is a higher resistance to oxidation.
Despite the paramagnetic nature of the complexes, proton NMR spectra could be obtained. The NMR signals spread over the range )20 to +90 ppm. The signals are relatively narrow and, for complexes 1 and 4 account for the two types of magnetically non-equivalent substituents on the b-diketonate ring, cis and trans to the nitrogen donor sites of the TMEDA ligand. The complexes with the aminoalcohols are more stereolabile and only one signal was observed at RT for the substituents of the b-diketonate ring. 3.2. Molecular structures of 1 and 2 The molecular structures of 1 and 2 were established by single crystal X-ray diffraction. 1 is monomeric (Fig. 2), while 2 contains two different dimeric molecules, 2a and 2b, in the asymmetric unit cell (Fig. 3). One molecule corresponds to the association of two monomeric units with chelating g2 -aminoalcohol ligands having an R configuration whereas the other involves chelating aminoalcohol ligands with an S configuration. The dimeric nature of 2 is due to assembly via hydrogen bonds from O(H) on one molecule to an O(acac) of another unit. The O–O distances have values of 2.684(3) for O(10)H–O0 (8) and O(5)H–O0 (4), and 2.733(3) A
Fig. 2. Molecular structure of Co(acac)2 (TMEDA) showing the atom numbering scheme (thermal ellipsoids at 20% probability).
Fig. 1. TGA curve of Co(acac)2 (TMEDA).
Fig. 3. Molecular structure of [Co(acac)2 (DMAPH)]2 showing the atom numbering scheme (dotted line indicate H bonding).
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respectively. Intramolecular hydrogen bonding in complexes with a b-diketonate ligand has been observed previously for instance for [Ba2 Cu(l3 ,g2 –OCHMeCH2 NMe2 )2 (l,g2 -thd)2 (g2 -thd)(i PrOH)2 ] (O–H–O av.) [33]. The structure of 2 is similar to that of 2.58 A [Ni(acac)2 (DMAEH)]2 [31] or [Ni(acac)2 (DMAPH)]2 av.). Selected bond distances and [34] (O–H–O 2.54 A angles are collected in Table 2. All adducts adopt a cis geometry, and the metals lie in a distorted octahedral CoO4 N2 or CoO5 N cores. The Co–O(g2 -acac) bond distances in 1 [2.043(4)–2.076(4) A] and 2 [2.023(3)–2.079(2) A], are similar to the literature body as illustrated by Co(acac)2 (6-methylquinoline) [35] or [Co(acac)2 (H2 O)]2 [36] for instance. The Co–O bonds are in 1 trans to the nitrogen atoms [2.076(4)–2.090(4) A] longer than those trans to the oxygenÕs [2.044(4) A av.]. A similar trans effect was observed for Co(acac)2 (TEEDA) [15] and Co(thtf)2 (TMEDA), thtf ¼ 1-(2thienyl)-4,4,4-trifluoro-1,3-butanedionate [37] but not for Co(acac)2 (bipy) [38,39]. The Co–O(H) coordination than bonds are as expected longer (2.112(2)–2.125(2) A) 2 the Co–O(g -acac) ones and similar to those observed in trans-Co(acac)2 (MeOH)2 [40]. The Co–N distances av. and 2.257(2) A av. for 1 and 2, respec[2.227(6) A tively] are comparable for both compounds. They are in agreement with the values on adducts N-donors such as N ; N ; N 0 ; N 0 -tetraethyl-1,2-diaminoethane [15], 6-methylquinoline [35] and pyridine [41], but longer than for instance for Co(thtf)2 (TMEDA) [37] or Co(acac)2 (bipy)
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for the a and b forms, [38,39] [2.161(3) and 2.147(5) A respectively]. The major distortions are related to the neutral ligands as observed for the bite angles N–Co–N [82.3(2)°] in 1 or the even smaller N–Co–O ones [78.10(9)° and 78.66(9)°] in 2 and to those related to the ligands in trans positions [
Table 2 and angles (°) of Co(acac)2 (TMEDA) and [Co(acac)2 (DMAPH)]2 Selected bond lengths (A) Co(acac)2 (TMEDA)
[Co(acac)2 (DMAPH)]2 Molecule a
Bond lengths Co–O(1) Co–O(2) Co–O(3) Co–O(4) Co–N(1) Co–N(2) Bond angles O(1)–Co–O(2) O(1)–Co–O(3) O(2)–Co–O(3) O(1)–Co–O(4) O(2)–Co–O(4) O(3)–Co–O(4) O(1)–Co–N(1) O(2)–Co–N(1) O(3)–Co–N(1) O(4)–Co–N(1) O(1)–Co–N(2) O(2)–Co–N(2) O(3)–Co–N(2) O(4)–Co–N(2) N(1)–Co–N(2)
2.076(4) 2.043(4) 2.090(4) 2.046(4) 2.237(5) 2.218(6) 88.1(1) 93.6(2) 90.8(2) 87.9(2) 175.2(2) 86.7(2) 174.6(2) 89.3(2) 91.2(2) 94.9(2) 93.3(2) 94.9(2) 171.2(2) 88.0(2) 82.3(2)
Co(1)–O(1) Co(1)–O(2) Co(1)–O(3) Co(1)–O(4) Co(1)–O(5) Co(1)–N(1) O(1)–Co(1)–O(2) O(1)–Co(1)–O(3) O(2)–Co(1)–O(3) O(1)–Co(1)–O(4) O(2)–Co(1)–O(4) O(3)–Co(1)–O(4) O(1)–Co(1)–O(5) O(2)–Co(1)–O(5) O(3)–Co(1)–O(5) O(4)–Co(1)–O(5) O(1)–Co(1)–N(1) O(2)–Co(1)–N(1) O(3)–Co(1)–N(1) O(4)–Co(1)–N(1) O(5)–Co(1)–N(1)
Molecule b 2.024(2) 2.039(2) 2.041(2) 2.079(2) 2.125(2) 2.252(2) 90.12(8) 96.2(1) 95.3(1) 176.23(9) 88.78(9) 87.44(9) 89.21(9) 93.68(9) 169.44(9) 87.27(9) 86.55(9) 171.16(9) 93.16(9) 94.02(9) 78.10(9)
Co(2)–O(7) Co(2)–O(6) Co(2)–O(9) Co(2)–O(8) Co(2)–O(10) Co(2)–N(2) O(6)–Co(2)–O(7) O(7)–Co(2)–O(9) O(6)–Co(2)–O(9) O(7)–Co(2)–O(8) O(6)–Co(2)–O(8) O(8)–Co(2)–O(9) O(7)–Co(2)–O(10) O(6)–Co(2)–O(10) O(9)–Co(2)–O(10) O(8)–Co(2)–O(10) O(7)–Co(2)–N(2) O(6)–Co(2)–N(2) O(9)–Co(2)–N(2) O(8)–Co(2)–N(2) O(10)–Co(2)–N(2)
2.032(2) 2.058(2) 2.023(3) 2.060(2) 2.112(2) 2.262(3) 89.8(1) 91.2(1) 95.2(1) 178.9(1) 89.58(9) 88.0(1) 90.7(1) 89.14(9) 175.3(1) 90.21(9) 87.8(1) 167.5(1) 97.1(1) 93.0(1) 78.66(9)
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behaviour of the precursors at lower and higher deposition temperature. Films of cubic Co3 O4 were deposited in all cases due to sufficient excess of oxygen during deposition and cooling (film thickness 100–400 nm). XRD study of Co3 O4 films deposited on LaAlO3 show that both precursors 1 and 4 give (1 1 0) textured films on LaAlO3 substrates (Fig. 4). Moreover, additional XRD study in Schultz geometry showed that films were grown epitaxially with ‘‘cubeon-cube’’ in-plane orientation of Co3 O4 crystallites. The formation of (1 1 0) texture during film growth can be explained by a better lattice match between the (0 0 1) plane of the pseudo-cubic substrates and the (1 1 0) plane of cubic Co3 O4 (mismatch 0.5%) compared to the (0 0 1) plane of Co3 O4 (6% mismatch). All Co3 O4 films deposited on Si(1 0 0) substrates were polycrystalline independently of the precursor and deposition temperature used. Films on Si were etched with HF in order to form a step for the determination of film thickness and growth rate. The use of Co(acac)2 (TMEDA) lead to higher growth rate (0.7 lm/h at 450 °C and 1.6 lm/h at 600 °C) compared to Co(thd)2 (TMEDA) (0.5 lm/h at 450 °C and 1.3 lm/h at 600 °C). Growth of Co3 O4 films from both precursors was kinetically limited in the temperature range 450–600 °C investigated. XPS studies of the deposited films were performed in the Co 2p, O 1s region. Fig. 5 shows an Al Ka XPS spectrum in the Co 2p, O 1s region of a film deposited at 600 °C using 1. The position of the Co 2p3=2 peak (780.5 eV), the presence of a weak shake up satellite at 790.5 eV and the value of the Auger a parameter (1553.5 eV)
Fig. 5. Part of an XPS spectrum showing the peaks of Co in Co3 O4 films deposited from Co(acac)2 (TMEDA) at 600 °C, the asterisk () indicates the weak shake up satellite.
confirmed that the film surface consisted of Co3 O4 [10]. Contamination with carbon (23%) could be reduced to 5.3% after sputtering of the surface by Arþ ions. These preliminary MOCVD experiments show that both new Co(II) b-diketonate adducts 1 and 4 can be applied for the deposition of pure, epitaxial Co3 O4 films by liquid injection MOCVD. They outperform the existing CVD precursors in terms of volatility and oxidation stability; the quite cheap, air stable Co(acac)2 (TMEDA) adduct is most attractive.
4. Supplementary material Crystallographic data (atomic coordinates, thermal parameters, full lists of bond distances and angles) have been deposited at the Cambridge Crystallographic Data Centre, CCDC No. 186320 and 171430 for 1 and 2, respectively. Copies of the data can be obtained free of charge from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ ccdc.com.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements The authors acknowledge partial financial support from European Community (FP5, MULTIMETOX network, contract C5RT-CT-1999-05001). S. Pasko is grateful to CNOUS (Centre National des Oeuvres Universitaires et Scolaires) for a fellowship.
References Fig. 4. XRD for Co3 O4 films deposited on LaAlO3 substrates from Co(acac)2 (TMEDA) at 450 and 600 °C. Similar scans were obtained in the case of Co(thd)2 (TMEDA).
[1] E. Fischer Rivera, B. Atakan, K. Kohse-H€ oinghaus, J. Phys. IV 11 (2001) Pr3-629.
S. Pasko et al. / Polyhedron 23 (2004) 735–741 [2] C.G. Granquist, Handbook of Inorganic Electrochromic Materials, Elsevier, Amsterdam, 1995. [3] M. Ando, T. Kobayashi, S. Iijima, M.J. Haruta, Mater. Chem. 7 (1997) 1779. [4] E. Barrera, I. Gonzalez, T. Viveros, Sol. Energy Mater. Solar Cells 51 (1998) 69. [5] A.U. Mane, K. Shalini, S.A. Shivashankar, J. Phys. IV 11 (2001) Pr3-63. [6] P.S. Patil, L.D. Kadam, C.D. Lokhande, Thin Solid Films 144 (1996) 29. [7] E. Fujii, H. Torii, A. Tomozawa, R. Takayama, T. Hirao, J. Mater. Sci. 30 (1995) 6013. [8] E. Fujii, Eur. Patent No EP0733 721A1, 1996. [9] T. Maruyama, T. Nakai, Sol. Energy Mater. 22 (1991) 107. [10] D. Barreca, C. Massignan, S. Daolio, M. Fabrizio, C. Piccirillo, L. Armelao, E. Tondello, Chem. Mater. 13 (2001) 588. [11] D.G. Colombo, D.C. Gilmer, V.G. Young, S.A. Campbell, W.I. Gladfelter, Chem. Vap. Dep. 4 (1998) 220. [12] T. Maruyama, Jpn. J. Appl. Phys., Part 2 36 (1997) 705L. [13] P.O. Dunstan, Thermochim. Acta 303 (1997) 209. [14] R.C. Aggarwal, D.S. Surya Narayana, Indian J. Chem. 21A (1982) 318. [15] R.E. Colborn, M.F. Garbauskas, C.I. Hejna, Inorg. Chem. 27 (1988) 3661. [16] G.C. Pellacani, R. Battistuzzi, G. Marcotrigliano, J. Inorg. Nucl. Chem. 35 (1973) 2243. [17] W. Ludwig, M. D€ oring, R. Fischer, A. Friedrich, W. Seidel, E. Uhlig, D. Walther, J. Therm. Anal. 38 (1992) 239. [18] D.S. Sankhla, R.C. Mathur, S.N. Misra, J. Inorg. Nucl. Chem. 42 (1980) 489. [19] A.Yu. Steblyanko, A.N. GrigorÕev, L.I. Martynenko, Russ. J. Inorg. Chem. 42 (1997) 215. [20] M.A. Laffey, P. Thornton, J. Chem. Soc., Dalton Trans. (1982) 313. [21] V.J. Eddy, J.L. Hallgreen, E. Robert, J. Polym. Sci. 28A (1990) 2417. [22] K. Kaeriyama, Makromol. Chem. 175 (1974) 2285. [23] H. Brunner, B. Hammer, Angew. Chem. 96 (1984) 305.
741
[24] J.B. Ellern, R.O. Ragsdale, Inorg. Syn. 11 (1968) 89. [25] D.J. Watkin, C.K. Prout, J.R. Carruthers, P.W. Betteridge, In: Crystal Issue 10; Chemical Crystallography Laboratory, University of Oxford, UK, 1996. [26] D.T. Cromer, in: International Tables for X-ray crystallography, vol. 4, Kynoch Press, Birmingham, 1974. [27] J.R. Carruthers, D.J. Watkin, Acta Cryst. A35 (1979) 698. [28] J.P. Senateur, C. Dubourdieu, V. Galindo, F. Weiss, A. Abrutis, in: Kwang-Leong Choy (Ed.), Innovative Processing of Films and Nanocrystalline Powders, Imperial College Press, London, 2002, p. 71. [29] A. Abrutis, V. Plausinaitiene, V. Kubilius, A. Teiserskis, Z. Saltyte, R. Butkute, J.P. Senateur, Thin Solid Films 413 (2002) 32. [30] A. Abrutis, V. Kubilius, V. Bigelyte, A. Teiserskis, Z. Saltyte, J.P. Senateur, F. Weiss, Mater. Lett. 31 (1997) 201. [31] P.A. Williams, A.C. Jones, J.F. Bickley, A. Steiner, H.O. Davies, T.J. Leedham, S.A. Impey, J. Garcia, S. Allen, A. Rougier, A. Blyr, J. Mater. Chem. 11 (2001) 2329. [32] H. Guillon, L.G. Hubert-Pfalzgraf, Appl. Organometal. Chem. 12 (1998) 231. [33] F. Labrize, L.G. Hubert-Pfalzgraf, J. Vaissermann, C.B. Knobler, Polyhedron 15 (1996) 577. [34] L.G. Hubert-Pfalzgraf, J. Vaissermann, unpublished results. [35] M.B. Hursthouse, K.M.A. Malik, J.E. Davies, J.H. Harding, Acta Cryst. B34 (1978) 1355. [36] F.A. Cotton, R.C. Elder, Inorg. Chem. 5 (1996) 423. [37] L.C. Tzavellas, C. Tsianis, C.A. Kavounis, C.J. Cardin, Inorg. Chim. Acta 262 (1997) 53. [38] A.N. GrigorÕev, A.Yu. Steblyanko, A.V. Goncharov, K.A. Potekhin, A.S. Batsanov, Yu.T. Struchkov, Russ. J. Inorg. Chem. 32 (1987) 396. [39] A.Yu. Steblyanko, A.N. GrigorÕev, L.I. Martynenko, M.V. Reshetnyak, A.S. Batsanov, Yu.T. Struchkov, Russ. J. Inorg. Chem. 33 (1988) 857. [40] P. Werndrup, V.G. Kessler, J. Chem. Soc., Dalton Trans. (2001) 574. [41] R.C. Elder, Inorg. Chem. 7 (1968) 1117. [42] L.G. Hubert-Pfalzgraf, Inorg. Chem. Commun. 6 (2003) 102.
Synthesis and molecular structures of cobalt(II) b-diketonate complexes as new MOCVD precursors for cobalt oxide films Sergej Pasko
a,b
, Liliane G. Hubert-Pfalzgraf a,*, Adulfas Abrutis Jacqueline Vaissermann c
b,*
,
a Universite Lyon 1, IRC-CNRS, 2 av. A. Einstein, 69626 Villeurbanne cedex, France Department of Chemistry, Vilnius University, Naugarduko 24, LT2006 Vilnius, Lithuania Laboratoire de Chimie des Metaux de transition, UMR-CNRS, 4 place Jussieu, Paris, France b
c
Received 17 September 2003; accepted 18 October 2003
Abstract Adducts of cobalt(II) 2,4-pentanedionate (acac) and 2,2,6,6-tetramethyl-3,5-heptanedionate (thd) with TMEDA (N ; N ; N 0 ; N 0 tetramethyl-1,2-diaminoethane) and aminoalcohols, namely 1-dimethylamino-2-propanol (DMAPH) and 2-dimethylaminoethanol (DMAEH), have been synthesized and characterized by elemental analyses, FT-IR, 1 H NMR, mass spectrometry and TGA. The molecular structures of Co(acac)2 (TMEDA) (1) and [Co(acac)2 (DMAPH)]2 (2) have been determined by single-crystal X-ray dif av.). The most fraction. 1 is monomeric while 2 is dimeric with two molecules linked by hydrogen bonds (O–H–O distance 2.708 A volatile and stable new adducts Co(acac)2 (TMEDA) and Co(thd)2 (TMEDA) have been studied as precursors for cobalt oxide deposition by liquid injection MOCVD in DME on monocrystalline LaAlO3 and Si substrates. Films were characterized by XRD and XPS. These preliminary MOCVD experiments showed that epitaxial Co3 O4 films can be obtained by using both new precursors. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Cobalt; Oxide; b-diketonates; Adducts; Structures; MOCVDf
1. Introduction Cobalt oxides are of great interest due to useful properties, such as high catalytic activity at low cost [1], antiferromagnetism [1], electrochromism [2]. Cobalt oxide films have been considered for uses as magnetic detectors, membranes for oxidation of hydrocarbons, counter electrodes, humidity or oxygen optical sensors [3,4], solar-selective absorbers and protective layers [1,5,6]. Cobalt oxide films have been deposited by a variety of methods including conventional MOCVD [1,2,5–8]. However, despite the interest of MOCVD of Co3 O4 , reports are scarce. [Co(acac)2 ]4 was generally used as a precursor [1,5,7,8], although the use of Co(acac)3 [8], Co(OAc)2 [9] and more recently of *
Corresponding authors. Tel.: +37052331004; fax: +37052330987. E-mail address: [email protected] (A. Abrutis).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2003.11.044
Co(thd)2 [10] or Co(NO3 )3 [11] has been reported. Another use of cobalt b-diketonates is for the CVD of Co films [12]. A number of cobalt(II) acetylacetonate adducts with N-donors have been described [13–18]. Although some of them such as Co(acac)2 (LL) [LL ¼ 2,20 -bipyridyl (130 °C/102 Torr), 1,10-phenantroline (190 °C/102 Torr)] [19] and Co2 (acac)4 (piperidine) (80 °C/104 Torr) [20] were volatile, no adduct was used so far for MOCVD applications. Cobalt b-diketonate adducts are also good catalysts for a number of reactions, such as polymerisation, enantioselective Michael addition, etc. [21–23]. We report here the synthesis and structural characterization of some new adducts of cobalt(II) 2,4-pentanedionate and 2,2,6,6-tetramethylheptane-3,5-dionate and the preliminary study of the most volatile and stable new adducts as precursors for the deposition of cobalt oxide films by liquid injection MOCVD.
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2. Experimental 2.1. Syntheses Syntheses of air-sensitive complexes were performed under argon using Schlenk tubes and vacuum line techniques. Solvents were purified by standard methods. TMEDA (N ; N ; N 0 ; N 0 -tetramethylethylenediamine), DMAEH (2-dimethylaminoethanol), DMAPH (1-dimethylamino-2-propanol), thdH (2,2,6,6-tetramethyl-3, 5-heptanedione) and acacH (acetylacetone, 2,4-pentanedione) were distilled and stored over molecular sieves. Co(thd)2 and Co(acac)2 (H2 O)2 were prepared as reported [10,24]. [Co(acac)2 ]4 was obtained by sublimation of Co(acac)2 (H2 O)2 at 100–120 °C/2 104 Torr (67%). It is slightly hygroscopic. FT-IR spectra were recorded with a Perkin–Elmer Paragon 500 Spectrometer as Nujol mulls. Mass spectra were obtained using a Thermofinnigan Mat95XL spectrometer under standard electron ionization conditions (E1 ¼ 70 eV). TGA experiments were performed under air with a Setaram 62 system using a thermal ramp of 10 °C/min. Proton NMR spectra were recorded in the range )130 to +130 ppm using the solvent peak as a reference on an AM250 Bruker spectrometer. Elemental analyses were done at the Centre de microanalyses du CNRS and at Vilnius University. Co(acac)2 (TMEDA) (1) was previously reported [15], it was prepared by a modified procedure. TMEDA (10% excess) was added to Co(acac)2 (H2 O)2 , the reaction medium was evaporated after 2 h and sublimed at 70 °C/2 104 Torr (90%). MS (m=zþ , %): M (5), M-acac (26), M-TMEDA (43), M-CH3 -TMEDA (76), M-acac-TMEDA (84), M-acac-CH3 -TMEDA (7), TMEDA (7), acacH (4), Me2 N@CH2 (100). 1 H NMR (CDCl3 , 20 °C): )13.19 broad (Me(acac) + CH, 8H), 10.51 s (6H, Me acac), 38.69 s (2H, CH2 ), 47 s (6H, Me2 N), 67 s (2H, CH2 ), 78.08 s (6H, Me2 N). [Co(acac)2 (DMAPH)]2 (2). 0.70 g (0.68 mmol) of [Co(acac)2 ]4 were dissolved in 20 ml of toluene and 0.37 ml (3.02 mmol) of DMAPH were added. The color of the solution changed from dark violet to red. After stirring for 2 h and concentration, 2 crystallized at )30 °C (0.72 g, 73%). Anal. Calc. for C15 H27 CoNO5 : C, 50.00; H, 7.55, N, 3.89. Found: C, 49.50; H, 7.49, N, 3.85%. IR, cm1 : 3390 w (mOH); 1599 vs, 1519 vs (mC@O, mC@C); 558 m, 505 w (mCo–O, mCo–N). 1 H NMR (CDCl3 , 20 °C): )14.52 s (2H, CH), 12.28 broad [15H, Me(acac) + Me(CH)], 32.85 broad (8H, Me2 N + CH2 ), 71.93 s (1H, CHO). [Co(acac)2 (DMAEH)] (3). 0.88 g (0.85 mmol) of [Co(acac)2 ]4 were dissolved in 25 ml of toluene. Addition of 0.38 ml (3.75 mmol) of DMAEH gave a red precipitate which was filtered after 16 h. A second crop of 3 was obtained by concentration at )30 °C (0.74 g, 72%). Anal. Calc. for C14 H25 CoNO5 : C, 48.56; H, 7.28;
N, 4.04. Found: C, 48.00; H, 7.30; N, 3.92%. IR, cm1 : 3109 w (mOH); 1595 vs, 1520 vs (mC@O, mC@C); 554 w (mCo–O, mCo–N). 1 H NMR (CDCl3 , 20 °C): )14.10 s (2H, CH), 12.13 s (12H, Me, acac), 32.85 broad (Me2 N + CH2 , 8H), 71.93 s (2H, CH2 O). Co(thd)2 (TMEDA) (4). Same procedure as for 2 applied to 0.32 g (0.75 mmol) of Co(thd)2 in 10 ml of toluene and 0.12 ml (0.83 mmol) of TMEDA. The reaction mixture was evaporated after 2 h and sublimed at 125 °C/2.3 102 Torr (80%). Anal. Calc. for C28 H54 CoO4 N2 : C, 62.09; H, 10.05, N, 5.17. Found: C, 62.73; H, 10.16, N, 5.40%. IR, cm1 : 1594 vs, 1582 vs, 1570 vs; 1531 s, 1504 vs (mC@O, mC@C); 609 w, 586 w, 478 m (mCo–O, mCo–N). MS (m=zþ , %): M (19), M-TMEDA (35), M-t Bu-TMEDA (100), M-C11 H19 O2 (10), MC11 H19 O2 -TMEDA (15). thdH (2.8), t BuCOCH2 CO (15), TMEDA (10). 1 H NMR (CDCl3 , 20 °C): )17.53 s (2H, CH), )5.09 s (18H, t Bu), 8.06 s (4H, Me2 N), 32.24 (18H, t Bu), 46.80 (2H, CH2 ), 67.82 (2H, CH2 ), 78.87 (12H, Me2 N). All compounds were soluble in usual organic solvents, except for 2 and 3, insoluble in aliphatic hydrocarbons. Solubility was generally lower in polar solvents (N ; N -dimethylformamide, CH3 CN, alcohols). All complexes but 1 are slightly air-sensitive, their colour changed to green on storage for over six months in air, oxidation to Co(III) was faster in solutions especially polar ones. 2.2. Crystallography of 1 and 2 Crystals of 1 and 2 were obtained by sublimation at 80–85 °C/2.3 102 Torr and by recrystallisation in toluene at )20 °C, respectively. Data were collected with an Enraf–Nonius MACH3 diffractometer. Unit cell dimensions with estimated standard deviations were obtained from least squares refinements of the setting angles of 25 well-centred reflections. Corrections were made for Lorentz and polarization effects. Empirical absorption correction (Difabs) was applied. Crystallographic data and other pertinent information are summarized in Table 1. Computations were performed using C R Y S T A L S [25]. Atomic form factors for neutral Co, O, N and C were taken from [26]. Anomalous dispersion was taken in account. All atoms were anisotropically refined. Hydrogen atoms were introduced in calculated positions. Least-squares refinements (full matrix) were carried out by minimizing the function P wðjFo j jFc jÞ2 , where Fo and Fc are the observed and calculated structure P factors. Models P reached converP gence with RP ¼ ðjjFo j jFc jjÞ= jFo j and Rw ¼ ½ ðjFo j jFc jÞ2 = wðFo Þ2 1=2 having values listed in Table 1. A weighting scheme [27] was applied. Criteria for a satisfactory complete analysis were the ratios of rms shift to standard deviation being less than 0.1 and no significant features in the final map.
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Table 1 Crystal data for Co(acac)2 (TMEDA) and [Co(acac)2 (DMAPH)]2 Formula Formula weight a (A) b (A) c (A) a (°) b (°) c (°) 3 ) V (A Z Crystal system Space group Linear absorption coefficient l (cm1 ) Density q (g cm3 ) Radiation h Limits (°) Temperature of measurement (K) Number of data collected Number of unique data collected Number P of unique data P used for refinement (on F ) R ¼ h kFo j jFc k= jFo j i1=2 P P wðjFo j jFc jÞ2 = wFo2 Rw ¼ Extinction parameter Number of variables 3 ) Largest difference peak and hole (e A
C16 H30 CoN2 O4 (1) 373.36 8.500(4) 10.193(3) 11.565(6) 90 92.35(4) 90 1001.0(7) 2 monoclinic Pn 8.71 1.24 Mo Ka (k ¼ 0:71069 A) 1–28 295 2720 2422 (Rint ¼ 0:03) 1764 ðFo Þ2 > 3rðFo Þ2 0.0476
C15 H27 CoNO5 (2) 360.3 10.674(2) 12.083(1) 14.452(2) 93.11(1) 91.96(2) 92.01(1) 1858.8 4 triclinic P 1 9.39 1.29 Mo Ka (k ¼ 0:71069 A) 1–26 251 7700 7288 (Rint ¼ 0:01) 4884 ðFo Þ2 > 3rðFo Þ2 0.0399
0.0525 691 210 0.40
0.0496 122 398 0.50
2.3. CVD experiments and films characterisation
3. Results and discussion
Deposition of Co3 O4 films was carried out by innovative pulsed liquid injection MOCVD (PI-MOCVD) [28]. Detailed description of this technique and of the reactor is given elsewhere [29,30]. Solutions (0.05 M) of precursors in 1,2-dimethoxyethane (monoglyme) were used for the depositions (injection frequency 2 Hz, microdose mass 4 mg). The carrier gas was a mixture of Ar (54 l/h) and O2 (36 l/h). Depositions were performed on monocrystalline LaAlO3 (1 0 0) and Si(1 0 0) substrates under 5 Torr total pressure. Substrates were cleaned in boiling toluene and its vapour before use. After deposition, films were cooled down to RT in an O2 atmosphere (1 atm). Films crystallization and texture were studied by Xray diffraction (XRD) with a Siemens D500 diffractometer (Cu Ka radiation). The film in-plane orientation was studied by XRD in Schultz geometry. X-ray photoelectron spectroscopy (XPS, VG ESCALAB 200R, Al Ka radiation) was also used. The in-depth film purity was evaluated after Arþ sputtering at 4 keV, 3.75 107 Torr argon pressure. A non-linear least-squares program (Eclipse V2.0) adopting Gaussian–Lorentzian peak shapes was used for the raw spectra fitting and for the evaluation of atomic compositions. Thickness of the films on Si(1 0 0) substrates was determined by profilometry (Taylor–Hobson) on a step formed by lithography. The thickness value was used for the calculation of the film growth rate.
3.1. Synthesis and characterization Adducts of cobalt(II) acetylacetonate with TMEDA, DMAEH and DMAPH were easily obtained either by ligand exchange reaction from Co(acac)2 (H2 O)2 or by decomplexation of [Co(acac)2 ]4 at RT. It is noticeable that the decomplexation of [Co(acac)2 ]4 by aminoalcohols was more effective than that of [Ni(acac)2 ]3 [31]. [Co(acac)2 ]4 by contrast did not react with O-donors such as DME, triglyme and tetraglyme even in refluxing toluene for 24 h. These observations account for the absence of decomplexation and/or ligand exchange reactions in DME solutions, the solvent used for the CVD experiments. Co(thd)2 and Co(thd)2 (TMEDA), the first adduct of Co(thd)2 reported, are also stable in DME. The complexes were characterized by elemental analyses, FT-IR, 1 H NMR, mass spectrometry and TGA. Their FT-IR spectra display the mC@O and mC@C absorption bands of the b-diketonate ligands in the 1504–1600 cm1 range as well as those of the Lewis base. The spectra of 2 and 3, the complexes with aminoalcohols, showed also absorptions at 3390 and 3109 cm1 , respectively, due to mOH stretching. Their frequency is lower than that of the corresponding free alcohol – 3433 and 3385 cm1 – respectively suggesting thus coordination. All compounds were volatile, the order of their sublimation rate under vacuum in identical conditions was as follows: Co(acac) 2 (TMEDA) >
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Co(thd)2 > Co(thd)2 (TMEDA) > [Co(acac)2 ]4 > [Co(aca c)2 (DMAPH)]2 [Co(acac)2 (DMAEH)]2 . The two latter adducts sublimed at 80 and 90 °C/104 Torr, respectively, but with partial loss of the aminoalcohol ligand especially for 3, the DMAEH adduct. Due to this behaviour, adducts 2 and 3 were not investigated as MOCVD precursors for cobalt oxide films. The complexes with TMEDA were totally recovered as adducts by sublimation under vacuum thus reflecting the higher thermal stability of the N,N-donor Co b-diketonate adducts as compared to those with the O,N-donors. The volatility of the tetramethylheptanedionate derivatives, is, as expected higher than that of the acetylacetonate ones except 1 [32]. TGA-DTA analyses were performed in air. Fig. 1 illustrates the data for 1. The amount of residue of black Co3 O4 (18.3%), lower than the theoretical amount (21.5%) and the almost horizontal DTA curve part show that 1 sublimed partially (15%) in the 130–230 °C temperature range. Subsequent events are the loss of TMEDA and acacH which occurred at temperatures lower than 260 °C and the oxidation of the residue as evidenced by the strong exothermic peak at 370 °C. The mass spectra of Co(acac)2 (TMEDA) (1) and of Co(thd)2 (TMEDA) (4) show the molecular ions, the stability being in the favour of 4. The main decomposition pathways of the molecular ions are the loss of TMEDA then of the methyl groups and acac for 1, of both TMEDA and butyl groups for 4. These patterns are in agreement with the literature. [10]. A peak at m=z ¼ 608 (25%) attributed to Co(thd)3 was observed for samples of 4 stored in air for 6 months. The oxidation rate to Co(III) species by air was 1 < 4 < 2 < [Co (acac)2 ]4 < Co(thd)2 < 3 according to 1 H NMR data. Thus, an advantage of the Co(II)-TMEDA adducts 1 and 4 by comparison to ligand free Co(II) b-diketonates is a higher resistance to oxidation.
Despite the paramagnetic nature of the complexes, proton NMR spectra could be obtained. The NMR signals spread over the range )20 to +90 ppm. The signals are relatively narrow and, for complexes 1 and 4 account for the two types of magnetically non-equivalent substituents on the b-diketonate ring, cis and trans to the nitrogen donor sites of the TMEDA ligand. The complexes with the aminoalcohols are more stereolabile and only one signal was observed at RT for the substituents of the b-diketonate ring. 3.2. Molecular structures of 1 and 2 The molecular structures of 1 and 2 were established by single crystal X-ray diffraction. 1 is monomeric (Fig. 2), while 2 contains two different dimeric molecules, 2a and 2b, in the asymmetric unit cell (Fig. 3). One molecule corresponds to the association of two monomeric units with chelating g2 -aminoalcohol ligands having an R configuration whereas the other involves chelating aminoalcohol ligands with an S configuration. The dimeric nature of 2 is due to assembly via hydrogen bonds from O(H) on one molecule to an O(acac) of another unit. The O–O distances have values of 2.684(3) for O(10)H–O0 (8) and O(5)H–O0 (4), and 2.733(3) A
Fig. 2. Molecular structure of Co(acac)2 (TMEDA) showing the atom numbering scheme (thermal ellipsoids at 20% probability).
Fig. 1. TGA curve of Co(acac)2 (TMEDA).
Fig. 3. Molecular structure of [Co(acac)2 (DMAPH)]2 showing the atom numbering scheme (dotted line indicate H bonding).
S. Pasko et al. / Polyhedron 23 (2004) 735–741
respectively. Intramolecular hydrogen bonding in complexes with a b-diketonate ligand has been observed previously for instance for [Ba2 Cu(l3 ,g2 –OCHMeCH2 NMe2 )2 (l,g2 -thd)2 (g2 -thd)(i PrOH)2 ] (O–H–O av.) [33]. The structure of 2 is similar to that of 2.58 A [Ni(acac)2 (DMAEH)]2 [31] or [Ni(acac)2 (DMAPH)]2 av.). Selected bond distances and [34] (O–H–O 2.54 A angles are collected in Table 2. All adducts adopt a cis geometry, and the metals lie in a distorted octahedral CoO4 N2 or CoO5 N cores. The Co–O(g2 -acac) bond distances in 1 [2.043(4)–2.076(4) A] and 2 [2.023(3)–2.079(2) A], are similar to the literature body as illustrated by Co(acac)2 (6-methylquinoline) [35] or [Co(acac)2 (H2 O)]2 [36] for instance. The Co–O bonds are in 1 trans to the nitrogen atoms [2.076(4)–2.090(4) A] longer than those trans to the oxygenÕs [2.044(4) A av.]. A similar trans effect was observed for Co(acac)2 (TEEDA) [15] and Co(thtf)2 (TMEDA), thtf ¼ 1-(2thienyl)-4,4,4-trifluoro-1,3-butanedionate [37] but not for Co(acac)2 (bipy) [38,39]. The Co–O(H) coordination than bonds are as expected longer (2.112(2)–2.125(2) A) 2 the Co–O(g -acac) ones and similar to those observed in trans-Co(acac)2 (MeOH)2 [40]. The Co–N distances av. and 2.257(2) A av. for 1 and 2, respec[2.227(6) A tively] are comparable for both compounds. They are in agreement with the values on adducts N-donors such as N ; N ; N 0 ; N 0 -tetraethyl-1,2-diaminoethane [15], 6-methylquinoline [35] and pyridine [41], but longer than for instance for Co(thtf)2 (TMEDA) [37] or Co(acac)2 (bipy)
739
for the a and b forms, [38,39] [2.161(3) and 2.147(5) A respectively]. The major distortions are related to the neutral ligands as observed for the bite angles N–Co–N [82.3(2)°] in 1 or the even smaller N–Co–O ones [78.10(9)° and 78.66(9)°] in 2 and to those related to the ligands in trans positions [
Table 2 and angles (°) of Co(acac)2 (TMEDA) and [Co(acac)2 (DMAPH)]2 Selected bond lengths (A) Co(acac)2 (TMEDA)
[Co(acac)2 (DMAPH)]2 Molecule a
Bond lengths Co–O(1) Co–O(2) Co–O(3) Co–O(4) Co–N(1) Co–N(2) Bond angles O(1)–Co–O(2) O(1)–Co–O(3) O(2)–Co–O(3) O(1)–Co–O(4) O(2)–Co–O(4) O(3)–Co–O(4) O(1)–Co–N(1) O(2)–Co–N(1) O(3)–Co–N(1) O(4)–Co–N(1) O(1)–Co–N(2) O(2)–Co–N(2) O(3)–Co–N(2) O(4)–Co–N(2) N(1)–Co–N(2)
2.076(4) 2.043(4) 2.090(4) 2.046(4) 2.237(5) 2.218(6) 88.1(1) 93.6(2) 90.8(2) 87.9(2) 175.2(2) 86.7(2) 174.6(2) 89.3(2) 91.2(2) 94.9(2) 93.3(2) 94.9(2) 171.2(2) 88.0(2) 82.3(2)
Co(1)–O(1) Co(1)–O(2) Co(1)–O(3) Co(1)–O(4) Co(1)–O(5) Co(1)–N(1) O(1)–Co(1)–O(2) O(1)–Co(1)–O(3) O(2)–Co(1)–O(3) O(1)–Co(1)–O(4) O(2)–Co(1)–O(4) O(3)–Co(1)–O(4) O(1)–Co(1)–O(5) O(2)–Co(1)–O(5) O(3)–Co(1)–O(5) O(4)–Co(1)–O(5) O(1)–Co(1)–N(1) O(2)–Co(1)–N(1) O(3)–Co(1)–N(1) O(4)–Co(1)–N(1) O(5)–Co(1)–N(1)
Molecule b 2.024(2) 2.039(2) 2.041(2) 2.079(2) 2.125(2) 2.252(2) 90.12(8) 96.2(1) 95.3(1) 176.23(9) 88.78(9) 87.44(9) 89.21(9) 93.68(9) 169.44(9) 87.27(9) 86.55(9) 171.16(9) 93.16(9) 94.02(9) 78.10(9)
Co(2)–O(7) Co(2)–O(6) Co(2)–O(9) Co(2)–O(8) Co(2)–O(10) Co(2)–N(2) O(6)–Co(2)–O(7) O(7)–Co(2)–O(9) O(6)–Co(2)–O(9) O(7)–Co(2)–O(8) O(6)–Co(2)–O(8) O(8)–Co(2)–O(9) O(7)–Co(2)–O(10) O(6)–Co(2)–O(10) O(9)–Co(2)–O(10) O(8)–Co(2)–O(10) O(7)–Co(2)–N(2) O(6)–Co(2)–N(2) O(9)–Co(2)–N(2) O(8)–Co(2)–N(2) O(10)–Co(2)–N(2)
2.032(2) 2.058(2) 2.023(3) 2.060(2) 2.112(2) 2.262(3) 89.8(1) 91.2(1) 95.2(1) 178.9(1) 89.58(9) 88.0(1) 90.7(1) 89.14(9) 175.3(1) 90.21(9) 87.8(1) 167.5(1) 97.1(1) 93.0(1) 78.66(9)
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S. Pasko et al. / Polyhedron 23 (2004) 735–741
behaviour of the precursors at lower and higher deposition temperature. Films of cubic Co3 O4 were deposited in all cases due to sufficient excess of oxygen during deposition and cooling (film thickness 100–400 nm). XRD study of Co3 O4 films deposited on LaAlO3 show that both precursors 1 and 4 give (1 1 0) textured films on LaAlO3 substrates (Fig. 4). Moreover, additional XRD study in Schultz geometry showed that films were grown epitaxially with ‘‘cubeon-cube’’ in-plane orientation of Co3 O4 crystallites. The formation of (1 1 0) texture during film growth can be explained by a better lattice match between the (0 0 1) plane of the pseudo-cubic substrates and the (1 1 0) plane of cubic Co3 O4 (mismatch 0.5%) compared to the (0 0 1) plane of Co3 O4 (6% mismatch). All Co3 O4 films deposited on Si(1 0 0) substrates were polycrystalline independently of the precursor and deposition temperature used. Films on Si were etched with HF in order to form a step for the determination of film thickness and growth rate. The use of Co(acac)2 (TMEDA) lead to higher growth rate (0.7 lm/h at 450 °C and 1.6 lm/h at 600 °C) compared to Co(thd)2 (TMEDA) (0.5 lm/h at 450 °C and 1.3 lm/h at 600 °C). Growth of Co3 O4 films from both precursors was kinetically limited in the temperature range 450–600 °C investigated. XPS studies of the deposited films were performed in the Co 2p, O 1s region. Fig. 5 shows an Al Ka XPS spectrum in the Co 2p, O 1s region of a film deposited at 600 °C using 1. The position of the Co 2p3=2 peak (780.5 eV), the presence of a weak shake up satellite at 790.5 eV and the value of the Auger a parameter (1553.5 eV)
Fig. 5. Part of an XPS spectrum showing the peaks of Co in Co3 O4 films deposited from Co(acac)2 (TMEDA) at 600 °C, the asterisk () indicates the weak shake up satellite.
confirmed that the film surface consisted of Co3 O4 [10]. Contamination with carbon (23%) could be reduced to 5.3% after sputtering of the surface by Arþ ions. These preliminary MOCVD experiments show that both new Co(II) b-diketonate adducts 1 and 4 can be applied for the deposition of pure, epitaxial Co3 O4 films by liquid injection MOCVD. They outperform the existing CVD precursors in terms of volatility and oxidation stability; the quite cheap, air stable Co(acac)2 (TMEDA) adduct is most attractive.
4. Supplementary material Crystallographic data (atomic coordinates, thermal parameters, full lists of bond distances and angles) have been deposited at the Cambridge Crystallographic Data Centre, CCDC No. 186320 and 171430 for 1 and 2, respectively. Copies of the data can be obtained free of charge from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ ccdc.com.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements The authors acknowledge partial financial support from European Community (FP5, MULTIMETOX network, contract C5RT-CT-1999-05001). S. Pasko is grateful to CNOUS (Centre National des Oeuvres Universitaires et Scolaires) for a fellowship.
References Fig. 4. XRD for Co3 O4 films deposited on LaAlO3 substrates from Co(acac)2 (TMEDA) at 450 and 600 °C. Similar scans were obtained in the case of Co(thd)2 (TMEDA).
[1] E. Fischer Rivera, B. Atakan, K. Kohse-H€ oinghaus, J. Phys. IV 11 (2001) Pr3-629.
S. Pasko et al. / Polyhedron 23 (2004) 735–741 [2] C.G. Granquist, Handbook of Inorganic Electrochromic Materials, Elsevier, Amsterdam, 1995. [3] M. Ando, T. Kobayashi, S. Iijima, M.J. Haruta, Mater. Chem. 7 (1997) 1779. [4] E. Barrera, I. Gonzalez, T. Viveros, Sol. Energy Mater. Solar Cells 51 (1998) 69. [5] A.U. Mane, K. Shalini, S.A. Shivashankar, J. Phys. IV 11 (2001) Pr3-63. [6] P.S. Patil, L.D. Kadam, C.D. Lokhande, Thin Solid Films 144 (1996) 29. [7] E. Fujii, H. Torii, A. Tomozawa, R. Takayama, T. Hirao, J. Mater. Sci. 30 (1995) 6013. [8] E. Fujii, Eur. Patent No EP0733 721A1, 1996. [9] T. Maruyama, T. Nakai, Sol. Energy Mater. 22 (1991) 107. [10] D. Barreca, C. Massignan, S. Daolio, M. Fabrizio, C. Piccirillo, L. Armelao, E. Tondello, Chem. Mater. 13 (2001) 588. [11] D.G. Colombo, D.C. Gilmer, V.G. Young, S.A. Campbell, W.I. Gladfelter, Chem. Vap. Dep. 4 (1998) 220. [12] T. Maruyama, Jpn. J. Appl. Phys., Part 2 36 (1997) 705L. [13] P.O. Dunstan, Thermochim. Acta 303 (1997) 209. [14] R.C. Aggarwal, D.S. Surya Narayana, Indian J. Chem. 21A (1982) 318. [15] R.E. Colborn, M.F. Garbauskas, C.I. Hejna, Inorg. Chem. 27 (1988) 3661. [16] G.C. Pellacani, R. Battistuzzi, G. Marcotrigliano, J. Inorg. Nucl. Chem. 35 (1973) 2243. [17] W. Ludwig, M. D€ oring, R. Fischer, A. Friedrich, W. Seidel, E. Uhlig, D. Walther, J. Therm. Anal. 38 (1992) 239. [18] D.S. Sankhla, R.C. Mathur, S.N. Misra, J. Inorg. Nucl. Chem. 42 (1980) 489. [19] A.Yu. Steblyanko, A.N. GrigorÕev, L.I. Martynenko, Russ. J. Inorg. Chem. 42 (1997) 215. [20] M.A. Laffey, P. Thornton, J. Chem. Soc., Dalton Trans. (1982) 313. [21] V.J. Eddy, J.L. Hallgreen, E. Robert, J. Polym. Sci. 28A (1990) 2417. [22] K. Kaeriyama, Makromol. Chem. 175 (1974) 2285. [23] H. Brunner, B. Hammer, Angew. Chem. 96 (1984) 305.
741
[24] J.B. Ellern, R.O. Ragsdale, Inorg. Syn. 11 (1968) 89. [25] D.J. Watkin, C.K. Prout, J.R. Carruthers, P.W. Betteridge, In: Crystal Issue 10; Chemical Crystallography Laboratory, University of Oxford, UK, 1996. [26] D.T. Cromer, in: International Tables for X-ray crystallography, vol. 4, Kynoch Press, Birmingham, 1974. [27] J.R. Carruthers, D.J. Watkin, Acta Cryst. A35 (1979) 698. [28] J.P. Senateur, C. Dubourdieu, V. Galindo, F. Weiss, A. Abrutis, in: Kwang-Leong Choy (Ed.), Innovative Processing of Films and Nanocrystalline Powders, Imperial College Press, London, 2002, p. 71. [29] A. Abrutis, V. Plausinaitiene, V. Kubilius, A. Teiserskis, Z. Saltyte, R. Butkute, J.P. Senateur, Thin Solid Films 413 (2002) 32. [30] A. Abrutis, V. Kubilius, V. Bigelyte, A. Teiserskis, Z. Saltyte, J.P. Senateur, F. Weiss, Mater. Lett. 31 (1997) 201. [31] P.A. Williams, A.C. Jones, J.F. Bickley, A. Steiner, H.O. Davies, T.J. Leedham, S.A. Impey, J. Garcia, S. Allen, A. Rougier, A. Blyr, J. Mater. Chem. 11 (2001) 2329. [32] H. Guillon, L.G. Hubert-Pfalzgraf, Appl. Organometal. Chem. 12 (1998) 231. [33] F. Labrize, L.G. Hubert-Pfalzgraf, J. Vaissermann, C.B. Knobler, Polyhedron 15 (1996) 577. [34] L.G. Hubert-Pfalzgraf, J. Vaissermann, unpublished results. [35] M.B. Hursthouse, K.M.A. Malik, J.E. Davies, J.H. Harding, Acta Cryst. B34 (1978) 1355. [36] F.A. Cotton, R.C. Elder, Inorg. Chem. 5 (1996) 423. [37] L.C. Tzavellas, C. Tsianis, C.A. Kavounis, C.J. Cardin, Inorg. Chim. Acta 262 (1997) 53. [38] A.N. GrigorÕev, A.Yu. Steblyanko, A.V. Goncharov, K.A. Potekhin, A.S. Batsanov, Yu.T. Struchkov, Russ. J. Inorg. Chem. 32 (1987) 396. [39] A.Yu. Steblyanko, A.N. GrigorÕev, L.I. Martynenko, M.V. Reshetnyak, A.S. Batsanov, Yu.T. Struchkov, Russ. J. Inorg. Chem. 33 (1988) 857. [40] P. Werndrup, V.G. Kessler, J. Chem. Soc., Dalton Trans. (2001) 574. [41] R.C. Elder, Inorg. Chem. 7 (1968) 1117. [42] L.G. Hubert-Pfalzgraf, Inorg. Chem. Commun. 6 (2003) 102.