Experimental and Molecular Dynamics Simulation Study of the Sublimation and Vaporization Energetics of Iron Metalocenes. Crystal Structures of Fe(η 5 -C 5 H 4 CH 3 ) 2 and Fe[(η 5 -(C 5 H 5 )(η 5 -C 5 H 4 CHO

Please download to get full document.

View again

All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
 25
 
  Experimental and Molecular Dynamics Simulation Study of the Sublimation and Vaporization Energetics of Iron Metalocenes. Crystal Structures of Fe(η 5 -C 5 H 4 CH 3 ) 2 and Fe[(η 5 -(C 5 H 5 )(η 5 -C 5 H 4 CHO
Share
Transcript
  Experimental and Molecular Dynamics Simulation Study of the Sublimation andVaporization Energetics of Iron Metalocenes. Crystal Structures of Fe( η 5 -C 5 H 4 CH 3 ) 2  andFe[( η 5 -(C 5 H 5 )( η 5 -C 5 H 4 CHO)] Cla ´ udio M. Lousada, † Susana S. Pinto, ‡ Jose ´  N. Canongia Lopes, ‡ M. Fa ´ tima Minas da Piedade, †,‡ Hermı ´ nio P. Diogo, ‡ and Manuel E. Minas da Piedade* ,†  Departamento de Quı ´ mica e Bioquı ´ mica, Faculdade de Cie ˆ ncias, Uni V  ersidade de Lisboa, 1649-016 Lisboa,Portugal, and Centro de Quı ´ mica Estrutural, Complexo Interdisciplinar, Instituto Superior Te ´ cnico daUni V  ersidade Te ´ cnica de Lisboa, 1049-001 Lisboa, Portugal Recei V  ed: No V  ember 11, 2007; In Final Form: December 18, 2007  The standard molar enthalpies of sublimation of ferrocene, 1,1 ′ -dimethylferrocene, decamethylferrocene,ferrocenecarboxaldehyde and  R -methylferrocenemethanol, and the enthalpy of vaporization of   N  ,  N  -dimethyl-(aminomethyl)ferrocene, at 298.15 K, were determined by Calvet-drop microcalorimetry and/or the Knudseneffusion method. The obtained values were used to assess and refine our previously developed force field formetallocenes. The modified force field was able to reproduce the  ∆ sub  H  ° m  and  ∆ vap  H  ° m  values of the test-setwith an accuracy better than 5 kJ ‚ mol - 1 , except for decamethylferrocene, in which case the deviation betweenthe calculated and experimental ∆ sub  H  ° m  values was 16.1 kJ ‚ mol - 1 . The srcin of the larger error found in theprediction of the sublimation energetics of decamethylferrocene, and which was also observed in the estimationof structural properties (e.g., density and unit cell dimensions), is discussed. Finally, the crystal structures of Fe( η 5 -C 5 H 4 CH 3 ) 2  and Fe[( η 5 -(C 5 H 5 )( η 5 -C 5 H 4 CHO)] at 293 and 150 K, respectively, are reported. Introduction The ability to predict macroscopic physical properties of asystem from a limited amount of molecular information has beena long-term goal in chemistry and engineering, as it reducesthe need for expensive and time-consuming experimentation.In the case of the enthalpy of sublimation of organometalliccompounds this problem has barely been investigated, in spiteof the fact that values of  ∆ sub  H  ° m  are often needed, for example,to obtain metal - ligand “bond strengths” from calorimetricstudies 1 - 3 or to design chemical vapor deposition processes. 4,5 In contrast, for organic compounds, a number of empiricalestimation schemes based on various structural motifs 6 - 13 andcorrelations with physical properties (e.g., the temperature of fusion), 14 and molecular parameters (e.g., the number of valenceelectrons or the van der Waals surface) 15 have been reported.The lack of experimental data 16 - 18 is perhaps the majorobstacle in the development of empirical correlations valid for,at least, homologous series of organometallic compounds. Thisseems to be possible, however, as shown by the good linearrelation observed by plotting the enthalpies of sublimation of M( η 5 -C 5 H 5 ) 2 Cl 2  (M  )  Ti, Zr, Hf, V, Nb, Ta, Mo, W)compounds against the atomic radii of the metals. 19 Anotherproblem is the large variety of combinations of metals andligands found in organometallic species, which makes thedevelopment of general empirical estimation methods moredifficult than for organic compounds.Although not a “paper and pencil” method, such as theschemes and correlations mentioned above, a much morepromising and general approach seems to be the use of atom - atom pair potential calculations. 20,21 This technique currentlyallows, to a considerable extent, the interpretation of packingeffects in many crystals and is being intensively applied (thoughstill with limited success) 22 - 24 in the investigation of the ab initioprediction of crystal structures, i.e., the prediction of crystalstructures based only on the knowledge of the molecularstructure. 15,21 - 25 It has also been used to estimate enthalpies of sublimation of organic compounds, 13,15,21 along with othercomputational methods, such as those based on neural net-works, 13 structure activity relationships 26,27 or PIXEL integration(integral sums over the molecular electron density to obtainCoulombic, polarization, dispersion, and repulsion lattice ener-gies). 28 Since the starting point for the prediction of  ∆ sub  H  ° m  bythe atom - atom method is the knowledge of the crystal structureof the compound of interest, the method does in principle allowfor the discrimination between different polymorphs, whichrepresents a considerable advantage over empirical procedures.A key aspect for the application of the atom - atom methodis the definition of an intermolecular potential function capableof accurately describing the interactions that simultaneouslydetermine the enthalpy of sublimation and the structure of thecrystal. Various potential functions and parametrizations havebeen developed, mainly for organic molecules, from statisticalanalysis of reported structure and enthalpy of sublimationdata. 20 - 22,25,29 In the case of organometallic compounds, anample structural databank is available 30 but, as mentioned above,very little information exists on enthalpies of sublimation. 16 - 18 Moreover, since the characterization of the solid samples interms of phase purity has been overlooked in most experimentalmeasurements of   ∆ sub  H  ° m , there are very few data that cansafely be assigned to a definite crystal structure and used asaccurate benchmarks to validate the calculations.This led us to embark on a systematic experimental andcomputational study of the quantitative relation between struc-ture and enthalpy of sublimation in organometallic compounds. * Author to whom correspondence should be addressed. E-mail: memp@fc.ul.pt. † Universidade de Lisboa. ‡ Instituto Superior Te´cnico da Universidade Te´cnica de Lisboa. 2977  J. Phys. Chem. A  2008,  112,  2977 - 298710.1021/jp7107818 CCC: $40.75 © 2008 American Chemical SocietyPublished on Web 03/11/2008  In a previous report a simple but transferable force field formetallocenes, integrated with the OPLS-AA model, was devel-oped and shown to correctly capture the volumetric propertiesof a number of solid ferrocene derivatives. 31 Although primarilydeveloped for solids, the model did not incorporate anyrestrictions regarding liquids. Hence its application to theprediction of the sublimation and vaporization energetics wasinvestigated in this work. The results of the computations wereassessed, and the model was refined using the enthalpies of sublimation of the solid compounds  1 - 5  and the enthalpy of vaporization of   6 , determined by Calvet-drop microcalorimetryand/or the Knudsen effusion method. Materials and MethodsGeneral.  Elemental analyses (C, H) were made on a FisonsInstruments EA1108 apparatus, with typical maximum accuracyerrors of  ( 0.3% for carbon and ( 0.1% for hydrogen. IR spectrawere carried out on Jasco 430, Jasco 4100, or Mattson satellitespectrophotometers, calibrated with polystyrene film.  1 H NMRspectra were obtained using a Varian Gemini 200 (300 MHz)or a Bruker Ultrashield (400 MHz) spectrometer. Mass spectrawere recorded on a Fisons Instruments Trio 1000 apparatus.X-ray powder diffractograms (XRD) were obtained at 293  (  2K, using Cu K R radiation, on D8 Bruker AXS, Philips PW1710,or Rigaku Geigerflex diffractometers. The data were collectedover the range 5 ° e 2 θ e 35  ° , with a scan speed of 0.5 °  (2 θ ‚ min - 1 ), and a step size 0.020 °  (2 θ ). The indexation of thepowder patterns was performed using the program Checkcell. 32 Differential scanning calorimetry (DSC) experiments were madewith a temperature-modulated TA Instruments 2920 MTDSCapparatus, operated as a conventional DSC. The samples weresealed under air in aluminum pans, and weighed to  (  10 - 7 gon a Mettler UMT2 ultra-microbalance. Helium (Air LiquideN55) at a flow rate of 0.5 cm 3 ‚ s - 1 was used as the purging gas.The temperature and heat flow scales of the instrument werecalibrated as previously described. 33 Materials. Fe( η 5 -C 5 H 5 ) 2 . Ferrocene ([CAS 102-54-5] Aldrich98%) was purified by sublimation at 328 K and 5.3 Pa prior touse. Elemental analysis for C 10 H 10 Fe: expected C 64.56%, H5.42%; found C 64.53%, H 5.39% (average of two determina-tions). FT-IR (KBr, main peaks):  ν ˜/cm - 1 ) 3083 ( ν C - H , C 5 H 5 );1105, 1408 ( ν C - C , C 5 H 5 ); 1001 ( δ C - H , C 5 H 5 ); 815, 850 ( π  C - H ,C 5 H 5 ); 475 ( ν Fe - C 5 H 5 ). The assignments were based on thosegiven by Nakamoto. 34 1 H NMR (400 MHz, CDCl 3  /TMS):  δ ) 4.173 (s, 10H, C 5 H 5 ). The  1 H NMR results are in agreementwith those reported in a reference database. 35 The powder patternwas indexed as monoclinic, space group  P 2 1  /  a , with  a ) 10.505-(6) Å,  b  )  7.589(9) Å,  c  )  5.912(6) Å,    )  120.9(6) ° . Thesevalues are in good agreement with  a ) 10.530(8) Å,  b ) 7.604-(5) Å,  c  )  5.921(4) Å,    )  121.0(6) °  previously obtained byneutron diffraction. 36 The onset ( T  on ) and the maximum ( T  max )temperature of the melting peak, obtained by DSC at a scanrate of 5 K ‚ min - 1 , were  T  on  )  447.73  (  0.12 K and  T  max  ) 448.51  (  0.07 K, respectively and the corresponding enthalpyof fusion  ∆ fus  H  ° m  )  17.81  (  0.06 kJ ‚ mol - 1 . The uncertaintiesquoted are twice the standard deviation of the mean of fourdeterminations. The samples had masses in the range of 4.2 - 6.2 mg. The previously reported enthalpies of fusion of ferroceneare in the range 17.8 - 18.5 kJ ‚ mol - 1 . 37 - 39 Fe( η 5 -C 5 H 4 CH 3 ) 2 .  1,1 ′ -Dimethylferrocene (CAS [1291-47-0], Aldrich 97%) was purified by sublimation at 296 K and 2.2Pa prior to use. Elemental analysis for C 12 H 14 Fe: expected C67.32%, H 6.59%; found C 67.52%, H 7.06% (average of twodeterminations). FT-IR (KBr, main peaks):  ν ˜/cm - 1 )  3077( ν C - H , C 5 H 5 ); 2966, 2944, 2919 ( ν C - H , CH 3 ); 2881, 1772, 1749,1729, 1698, 1683, 1651; 1474, 1462 (symmetric bending CH 3 );1379 (asymmetric bending CH 3 ); 1359 ( ν C - C , in-plane skeletalvibration); 1226 ( ν C - CH 3 ); 1054, 1037 ( δ C - H ); 1024 (ringbreathing); 924, 918; 850 ( δ C - C ); 811 (out-of-plane bend  π  C - H perpendicular); 633, 602 ( δ C - C ); 502 (asymmetric  ν Fe - C 5 H 5 CH 3 );479 (asymmetric  δ Fe - C 5 H 5 CH 3 ). The assignments were based onthose given by Phillips et al. 40 1 H NMR (300 MHz, CDCl 3  / TMS):  δ  )  1.935 (s, 6H, CH 3 ); 3.990 (s, 8H, C 5 H 4 ), in goodagreement with previously reported data. 41 The powder patternwas indexed as monoclinic, space group  P 2 1  /  c , with  a ) 12.236-(4) Å,  b  )  7.483(6) Å,  c  )  10.803(4) Å,    )  103.6(5) ° . Thesevalues are in agreement with  a  )  12.334(6) Å,  b  )  7.526(3)Å,  c  )  10.954(4) Å,    )  102.81(2) obtained in this work at293 K by single-crystal X-ray diffraction. The onset and themaximum temperature of the melting peak, obtained by DSCat a scan rate of 10 K ‚ min - 1 , were  T  on  )  311.55  (  0.11 K and T  max  )  312.60  (  0.21 K, respectively, and the correspondingenthalpy of fusion  ∆ fus  H  ° m  )  17.66  (  0.06 kJ ‚ mol - 1 . Theuncertainties quoted are twice the standard deviation of the meanof four determinations. The samples had masses in the range3.8 mg to 4.9 mg. Fe[ η 5 -C 5 (CH 3 ) 5 ] 2 .  Decamethylferrocene (CAS [12126-50-0],Aldrich 97%) was purified by sublimation at 413 K and 5.3Pa. Elemental analysis for C 20 H 30 Fe: expected C 73.62%, H9.27%; found C 73.42%, H 9.12% (average of two determina-tions). FT-IR (KBr, main peaks):  ν ˜/cm - 1 )  2965, 2945, 2896( ν C - H , CH 3 ); 1377, 1373 (symmetric bending CH 3 ); 1473, 1449,1426 (asymmetric bending CH 3 ); 1356 ( ν C - C , in-plane skeletalvibration); 587 (ring breathing); 453 (asymmetric  ν Fe - C 5 H 5 CH 3 ).These results agree with those published by Stanghellini andco-workers. 42 1 H NMR (300 MHz, CDCl 3  /TMS):  δ  )  1.63 (s,30H, C 5 (CH 3 ) 5 ). The powder pattern was indexed as orthor-hombic space group  C  mca ,  a  )  15.238(6) Å,  b  )  11.919(5) Å, c ) 9.862(9) Å. These values are in agreement with  a ) 15.210-(3) Å,  b  )  11.887(2) Å,  c  )  9.968(2) Å, obtained by single-crystal X-ray diffraction. 43 Two endothermic events, corre-sponding to solid - solid phase transitions were detected beforefusion, by DSC. For the first transition  T  on  )  401.11  (  0.05 K, T  max  )  402.55  (  0.04 K and  ∆ trs  H  ° m  )  4.30  (  0.04 kJ ‚ mol - 1 ;for the second transition  T  on ) 503.12 ( 0.11 K,  T  max ) 503.74 (  0.08 K, and  ∆ trs  H  ° m  )  4.87  (  0.05 kJ ‚ mol - 1 . Fusionoccurred with partial decomposition of the sample at  T  on  ) 2978  J. Phys. Chem. A, Vol. 112, No. 13, 2008   Lousada et al.  576.89  (  0.15 K and  T  max  )  577.32  (  0.09 K (average of twodeterminations). The DSC experiments were carried out at ascan rate of 5 K ‚ min - 1 using masses of sample in the range 3.5mg to 6.6 mg. Fe[( η 5 -C 5 H 5 )( η 5 -C 5 H 4 CHO)].  Ferrocenecarboxaldehyde (CAS[12093-10-6], Aldrich 98%) was purified by sublimation at 298K and 1.1 Pa. Elemental analysis for C 11 H 10 OFe: expected C61.73%, H 4.71%; found C 61.51%, H 4.56% (average of twodeterminations). FT-IR (KBr, main peaks):  ν ˜/cm - 1 )  3087( ν C - H , C 5 H 5 ); 2866, 2833, 2804, 2762, 2727 ( ν C - H , CHO); 1680( ν C - O , CHO); 1105, 1410 ( ν C - C , C 5 H 5 ); 1388 ( δ C - H , CHO);1001 ( δ C - H , C 5 H 5 ); 823, 841 ( π  C - H , C 5 H 5 ); 498 (C 5 H 5  ring tilt);480 ( ν Fe - C 5 H 5 ).  1 H NMR (400 MHz, CDCl 3  /TMS):  δ  )  4.271(5H, C 5 H 5 ), 4.604 (2H, C 5 H 4 ), 4.791 (2H, C 5 H 4 ), 9.949 (1H,CHO). The observed FT-IR and  1 H NMR spectra are in goodagreement with those indicated in a reference database. 35 TheX-ray powder pattern was indexed as orthorhombic, space group P 2 1 2 1 2 1 , with  a  )  7.597(7) Å,  b  )  10.448(4) Å,  c  )  11.241(3)Å. These values are in agreement with those previously reportedfrom single-crystal X-ray diffraction experiments carried outat room temperature  a  )  7.639(5) Å,  b  )  10.525(8) Å,  c  ) 11.294(10) Å. 44 A solid - solid phase transition with  ∆ trs  H  ° m  ) 11.6  (  0.3 kJ ‚ mol - 1 , was observed by DSC at  T  on  )  316.2  ( 0.2 K and  T  max  )  317.4  (  0.3 K. This was followed by fusionat  T  on  )  396.6  (  0.2 K,  T  max  )  397.2  (  0.2 K, for which ∆ fus  H  ° m  )  2.5  (  0.2 kJ ‚ mol - 1 . The uncertainties quoted aretwice the standard deviation of the mean of four determinations.The obtained values are in good agreement with the DSC resultspreviously reported by Daniel et al. ( T  trs  )  316.4 K;  ∆ trs  H  ° m  ) 11.7  (  0.3 kJ ‚ mol - 1 ,  T  fus )  396.7 K,  ∆ fus  H  ° m )  2.05  (  0.06 kJmol - 1 ) 45 and in reasonable agreement with the more recentadiabatic calorimetry determinations by Kaneko and Sorai ( T  trs )  317.03 K;  ∆ trs  H  ° m  )  13.29  (  0.10 kJ ‚ mol - 1 ,  T  fus )  397.60K,  ∆ fus  H  ° m  )  2.76 kJ mol - 1 ). 46 The experiments were carriedout at a scan rate of 5 K ‚ min - 1 , using samples with masses inthe range of 3.3 - 6.7 mg. Fe[( η 5 -C 5 H 5 )( η 5 -C 5 H 4 CHCH 3 OH)]. R -Methylferrocenemeth-anol (CAS [1277-49-2], Aldrich 97%; racemic mixture) waspurified by sublimation at 310 K and 1.5 Pa, followed byrecrystallization from petroleum ether 40 - 60 ° . Elementalanalysis for C 12 H 14 OFe: expected C 62.65%, H 6.13%; foundC 62.86%, H 6.08% (average of two determinations). FT-IR(KBr, main peaks):  ν ˜/cm - 1 )  3924 ( ν C - H , C 5 H 5 ); 3213, 3088,2973, 2930, 1635, 1410, 1363, 1307, 1237, 1105, 1068, 1000( δ C - H , C 5 H 5 ); 917, 869, 807 ( π  C - H , C 5 H 5 ); 511 (C 5 H 5  ring tilt);482, 4366 ( ν Fe - C 5 H 5 ).  1 H NMR (400 MHz, CDCl 3  /TMS):  δ  ) 4.548 (m, 1H, CH), 4.197 (m, 9H, C 5 H 4  and C 5 H 5 ), 1.823 (d,2H, OH), 1.432 (d, 3H, CH 3 ). The observed  1 H NMR spectrumis in good agreement with that reported in the literature. 47 TheX-ray powder pattern was indexed as tetragonal, space group  I  4 1 cd  , with  a ) b ) 23.293(0) Å,  c ) 7.710(2) Å. These valuesare in agreement with those obtained by single-crystal X-raydiffraction  a  )  b  )  23.3334(18) Å,  c  )  7.7186(11) Å. 48 Theonset and the maximum temperature of the fusion peak obtainedby DSC at a scan rate of 5 K ‚ min - 1 were  T  on  )  335.56  (  0.11K and  T  max  )  343.71  (  0.09 K, respectively, and thecorresponding enthalpy of fusion  ∆ fus  H  ° m  )  14.75  (  0.06kJ ‚ mol - 1 . The uncertainties quoted are twice the standarddeviation of the mean of four determinations. The samples hadmasses in the range of 5.2 - 7.1 mg. Fe[( η 5 -C 5 H 5 ) { η 5 -C 5 H 4 CH 2 N(CH 3 ) 2 } ].  N  ,  N  -Dimethyl(ami-nomethyl)ferrocene (CAS [1271-86-9], Aldrich 96%, F) 1.228g ‚ cm - 3 ) was purified by distillation at 373 K and 1.1 Pa. FT-IR (NaCl windows, main peaks):  ν ˜/cm - 1 )  3092, 2966, 2937,2854, 2813, 2764, 2720, 1685, 1467, 1455, 1438, 1412, 1380,1348, 1260, 1231, 1171, 1136, 1105, 1039, 1021, 1001, 928,843.  1 H NMR (400 MHz, CDCl 3  /TMS):  δ  )  4.15 (5H, C 5 H 5 );4.10 (4H, C 5 H 4 ), 3.26 (2H, R 2 NCH 2 Cp), 2.16 (6H, (H 3 C) 2 N - ).Mass spectrum (70 eV, sample temperature 302 K, sourcetemperature 523 K):  m  /   z  (relative intensities)  )  244 (10.93),243 (67.33), 242 (22.57), 241 (9.50), 201 (3.67), 200 (23.49),199 (86.50), 197 (9.69), 187 (2.73), 186 (27.27), 178 (4.13),177 (4.12), 175 (8.29), 163 (20.40), 162 (29.44), 135 (10.34),134 (14.64), 129 (5.65), 122 (16.17), 121 (100.0), 119 (11.93),106 (5.88), 99 (7.92), 97 (5.37), 95 (6.86), 94 (12.45), 83 (3.00),81 (8.97), 79 (6.46), 78 (12.78), 77 (11.94), 65 (5.89), 58(21.80), 56 (49.48), 44 (6.05), 42 (26.20). The observed FT-IR,  1 H NMR and mass spectra are in good agreement with thoseindicated in a reference database. 35 The onset and the maximumtemperatures of the fusion peak obtained by DSC, using sampleswith masses in the range of 2.9 - 5.8 mg and a scan rate of 5K ‚ min - 1 , were  T  on  )  278.40  (  0.13 K and  T  max  ) 281.46  ( 0.09 K, respectively, and the corresponding enthalpy of fusion ∆ fus  H  ° m  )  14.6  (  0.2 kJ ‚ mol - 1 . The uncertainties quoted aretwice the standard deviation of the mean of four determinations.These results are in reasonable agreement with the previouslyreported  T  fus  )  280.94  (  0.01 K and  ∆ fus  H  ° m  )  15.01  (  0.02kJ ‚ mol - 1 . 49 Single-Crystal X-ray Diffraction.  Single-crystal X-ray dif-fraction analysis of dimethylferrocene was performed at 293 Kon a MACH3 Enraf-Nonius diffractometer equipped with MoK R radiation (  λ ) 0.710 73 Å). Data were corrected for Lorentzand polarization effects, and for absorption, using the DIFABSempirical method included in WINGX-Version 1.70.01. 50 Datacollection and data reduction were done with the CAD4 andXCAD programs. 51 In the case of ferrocenecarboxaldehyde theanalysis was carried out at 150 K on a Bruker AXS APEX CCDarea detector diffractometer, using graphite-monochromated MoK R  (  λ  )  0.710 73 Å) radiation. Intensities were corrected forLorentz polarization effects. An empirical absorption correctionwas applied using SADABS, 52 and the data reduction was donewith the SMART and SAINT programs. 53 All structures weresolved by direct methods with SIR97 54 and refined by full-matrixleast-squares on  F  2 using SHELXL97, 55 both included inWINGX-Version 1.70.01. 50 Non-hydrogen atoms were refinedwith anisotropic thermal parameters whereas H atoms wereplaced in idealized positions and allowed to refine riding onthe parent C atom. Graphical representations were preparedusing ORTEP 56 and Mercury 1.1.2. 57 The PARST program 58 was used to calculate intermolecular interactions in both cases.A summary of the crystal data, structure solution and refinementparameters is given in Table 1. Knudsen Effusion Experiments.  The Knudsen effusionapparatus used to determine the enthalpies of sublimation of Fe( η 5 -C 5 H 5 ) 2 , Fe( η 5 -C 5 H 4 CH 3 ) 2 , Fe[ η 5 -C 5 (CH 3 ) 5 ] 2 , and Fe[( η 5 -C 5 H 5 )( η 5 -C 5 H 4 CHO)] has been previously described. 19,59,60 Theeffusion holes were drilled in a 2.090  ×  10 - 5 m thick copperfoil (Cu 99%, Goodfellow Metals) soldered to the cell lid andhad areas of 6.952  ×  10 - 7 m 2 (hole 1; ferrocene), 4.390  ×  10 - 7 m 2 (hole 2; 1,1 ′ -dimethylferrocene, and decamethylferrocene),and 6.910  ×  10 - 7 m 2 (hole 3; ferrocenecarboxaldehyde). In thecase of Fe( η 5 -C 5 H 5 ) 2 , Fe( η 5 -C 5 H 4 CH 3 ) 2 , and Fe[( η 5 -(C 5 H 5 )( η 5 -C 5 H 4 CHO)] this block was immersed in a water bath whosetemperature was controlled to  ( 0.01 K with a Haake EDUnitherm thermostat and measured with the same precision witha calibrated mercury thermometer. A Haake EK12 cryostat wasused as a heat sink. In the experiments with Fe[ η 5 -C 5 (CH 3 ) 5 ] 2 the water bath was replaced by a tubular furnace surroundingIron Metalocenes  J. Phys. Chem. A, Vol. 112, No. 13, 2008   2979  the brass block. The temperature was controlled to better than ( 0.1 K, by a Eurotherm 902P thermostatic unit, and a K typethermocouple placed in contact with the inner wall of thefurnace. The temperature of the brass block was measured witha precision of   ( 0.1 K by a Tecnisis 100 Ω platinum resistancethermometer embedded in the block and connected in a fourwire configuration to a Keithley 2000 multimeter. The equi-librium temperature inside the cell was assumed to be identicalto the temperature of the water bath or of the brass block,respectively. The cells were initially charged with ca. 0.2 - 0.5g of sample, and the mass loss in each run was determined to ( 10 - 5 g with a Mettler AT201 balance. Calvet Microcalorimetry.  The enthalpies of sublimation of Fe( η 5 -C 5 H 5 ) 2 , Fe( η 5 -C 5 H 4 CH 3 ) 2 , Fe[( η 5 -C 5 H 5 )( η 5 -C 5 H 4 CHO)]and Fe[( η 5 -(C 5 H 5 )( η 5 -C 5 H 4 CHCH 3 OH)], and the enthalpy of vaporization of Fe[( η 5 -C 5 H 5 ) { η 5 -C 5 H 4 CH 2 N(CH 3 ) 2 } ] were alsomeasured by using the electrically calibrated Calvet microcalo-rimeter and the operating procedure previously reported. 61,62 Ina typical experiment the sample with a mass in the range 2 - 22mg was placed into a small glass capillary and weighed with aprecision of 1  µ g in a Mettler M5 microbalance. The capillarywas equilibrated for ca. 10 min, at  T   )  298.15 K, inside afurnace placed above the entrance of the calorimetric cell, andsubsequently dropped into the cell under N 2  atmosphere. Thetemperature of the calorimetric cell was set to 298.15 K forFe( η 5 -C 5 H 5 ) 2  and Fe( η 5 -C 5 H 4 CH 3 ) 2 , 311.2 K for Fe[( η 5 -C 5 H 5 )-( η 5 -C 5 H 4 CHO)], 311.0 K for Fe[ η 5 -C 5 H 5 )( η 5 -C 5 H 4 CHCH 3 OH)],and 305.1 K for Fe[( η 5 -C 5 H 5 ) { η 5 -C 5 H 4 CH 2 N(CH 3 ) 2 } ]. Afterdropping, an endothermic peak due to the heating of the samplefrom room temperature to the temperature of the calorimeterwas first observed. When the signal returned to the baselinethe sample and reference cells were simultaneously evacuatedto 1.3  ×  10 - 4 Pa and the measuring curve corresponding to thevaporization or sublimation of the compound was acquired. Thecorresponding enthalpy of sublimation or vaporization wassubsequently derived from the area of the obtained curve andthe calibration constant of the apparatus. No decompositionresidues were found inside the calorimetric cell at the end of the experiments. Density Functional Theory Calculations.  Density functionaltheory calculations were carried out with the Gaussian-03program. 63 The geometries were fully optimized and the totalenergies were calculated using the Becke’s three-parameterhybrid method 64 with the Perdew and Wang PW91 65 correlationfunctional (B3PW91) and the SDDall basis set (SDD effectivecore potentials and triple-   valence basis sets on all heavy atomsand D95 for hydrogens). 66,67 In previous tests the B3PW91/ SDDall model proved to be a reliable, economical, and practicalapproach to obtain accurate geometrical data for ferrocenederivatives. 31 All the total energies, given as SupportingInformation, were corrected with the zero-point vibrationenergies calculated at the same theoretical level. Atomic pointcharges (ESP charges) were determined at the BPW91/6-311G-(3df,3pd) level of theory, through a fit to the molecularelectrostatic potential, using the CHelpG procedure 68 and theBPW91/SDDall equilibrium geometry. Molecular Dynamics (MD) Simulations.  The moleculardynamics runs were performed using the DL • POLY package 69 and a refined version of the previously reported all-atom forcefield developed to model ferrocene and its derivatives withinthe framework of the OPLA • AA parametrization. 31 In theformer version of the force field the five carbon atoms of thecyclopentadienyl (Cp) ring and the five atoms attached to them(either hydrogens or the atoms from substituents directlyinvolved in the bond to the Cp ring) were considered as a rigidunit. The remaining fragments of the ring substituents weremodeled using the corresponding OPLS-AA (or AMBER) bond,angle, dihedral and improper dihedral constraints. This wassubsequently found to lead to convergence problems during thesimulation of some ferrocene derivatives. To overcome thisproblem, it was assumed in the present refinement of the forcefield that the five “backbone” carbon atoms of the Cp ring stillform a rigid unit but all Cp ring substituents (any atom attacheddirectly or indirectly to the backbone carbon atoms) are modeledusing the usual OPLS-AA (or AMBER) parameters. 70 - 73 Theonly other departure from the previously reported force field 31 was related to the nonbonded interactions (Lennard-Jonesparameters) of the iron atom. Preliminary simulations using thewhole Cp ring as a rigid unit yielded  ∆ sub  H  ° m [Fe( η 5 -C 5 H 5 ) 2 ]  ) 76  (  3 kJ ‚ mol - 1 at 298.15 K, 31 in good agreement with therecommended value of 73.48  (  1.08 kJ ‚ mol - 1 for the use of ferrocene as a standard reference material for enthalpy of sublimation measurements. 17,74 However, when the constraintof rigid Cp substituents was waived, significant overestimationsof the standard molar enthalpy of sublimation of ferrocene andother ferrocene-derivatives were observed. A closer inspectionat the parameters used for the iron atom in the nonrefined forcefield showed that the nonbonded interaction parameter  ǫ  (thatwas adapted from a Buckingham-type potential fitted tosimulation data performed on a rigid ferrocene model) 75 wastoo high in the context of the OPLS-AA framework, particularlywhen only the backbones of the metallocene molecules weremodeled as rigid units. We therefore decided to modify the  ǫ parameter for iron in order to match the simulation results withthe average of the experimental values for the standard molarenthalpy of sublimation of ferrocene obtained in this work by TABLE 1: Crystal Data and Structure Refinement for1,1 ′ -Dimethylferrocene and Ferrocenecarboxaldehyde Fe( η 5 -C 5 H 4 CH 3 ) 2 Fe[( η 5 -C 5 H 5 )-( η 5 -C 5 H 4 CHO)]empirical formula C12 H14 Fe C11 H10 Fe Oformula weight 214.08 214.04 T   /K 293(2) K 150(1) Kwavelength/Å 0.71073 0.71073crystal size/mm 0.17  ×  0.15  ×  0.11 0.2  ×  0.2  ×  0.2color of crystal orange redcrystal system monoclinic orthorhombicspace group  P 2 1  /  a P 2 1 2 1 2 1 a  /Å 10.954(4) 7.639(6) b  /Å 7.526(3) 10.518(8) c  /Å 12.334(6) 11.300(9)    /deg 102.81(2) V   /Å 3 991.5(7) 907.9(12)  Z   4 4 F calcd  /g ‚ cm - 3 1.434 1.566  µ  /mm - 1 1.467 1.610 F  (000) 448 440 θ  limits/deg 1.69 - 25.07 2.65 - 28.37limiting indices 0 e h e 12  - 10 e h e 90 e k e 8  - 14 e k e 11 - 14 e 1 e 14  - 15 e 1 e 14reflns collected/unique 1675/1675[  R (int) ) 0.0000]5487/2246[  R (int) ) 0.0576]completeness to  θ  95.5% ( θ ) 25.07) 99.2% ( θ ) 28.37)refinement method full-matrix least-squares on  F  2 full-matrix least-squares on  F  2 data/restraints/params 1675/0/118 2246/1/118GOF on  F  2 1.023 1.000final  R  indices [  I  > 2 σ  (  I  )]  R 1 ) 0.0798  R 1 ) 0.0541  R  indices (all data)  R 1 ) 0.1041  R 1 ) 0.0988absolute structure param 0.10(6)largest diff peak andhole/e ‚ Å - 3 1.221 and - 1.114 0.456 and - 0.338 2980  J. Phys. Chem. A, Vol. 112, No. 13, 2008   Lousada et al.  Knudsen effusion and Calvet microcalorimetry (73 kJ ‚ mol - 1 ,see below). The new value of   ǫ  for the iron atom, used in allsimulations reported in this paper, is 1.2 kJ ‚ mol - 1 . It must bestressed that the decision of using the  ǫ  parameter for iron as afitting variable, and retain the OPLS-AA parameters for all otheratoms, was based on the rationale behind the development of the present force-field: 31 a model for the prediction of theproperties of organometallic compounds that is compatible withthe OPLS-AA parametrization for their organic fragments.The condensed phases were modeled as boxes containing anumber of molecules ranging from 144 (decamethylferrocene)to 280 (ferrocene), which correspond to an average number of atoms of around 6000 and to cutoff distances of 1.6 nm. TheEwald summation technique was used to account for long-rangeinteractions beyond those cutoffs. In the case of the solidcompounds, the simulation boxes and initial configurations wereset taking into account the dimensions and occupancy of theunit cells of the crystalline structures at various temperaturesselected from the Cambridge Structural Database (CSD) 30 (ferrocene CSD ref codes, FEROCE04-06, 13, 24, 27, 29,31; 36,76 - 78 1,1 ′ -dimethylferrocene CSD ref code, ZAYDUY; 79 decamethylferrocene CSD ref code, DMFERR01; 43 ferrocen-ecarboxaldehyde CSD ref code, DEJZAT; 44 R -methylferrocen-emethanol CSD ref code, HIDXOH 48 ) or obtained in this workfor 1,1 ′ -dimethylferrocene and ferrocenecarboxaldehyde. Sincethe dimensions of the unit cells of the crystals were too smallto accommodate a sufficiently large cutoff distance, well-proportioned simulation boxes consisting of several stacked cellswere used. The simulations were performed under the aniso-tropic isothermal - isobaric ensemble (  N- σ  -T  ) at 298 K and 0.1MPa and typical runs consisted of an equilibration period of ca. 100 ps followed by production stages of 400 ps. Other detailsconcerning the simulation of crystalline structures using anOPLS-based force field can be found elsewhere. 31,80 In the caseof the liquid  N  ,  N  -dimethyl(aminomethyl)ferrocene, 200 mol-ecules were randomly placed in a large cubic box (using anexpanded cubic lattice to avoid superimposition) and the systemwas allowed to evolve for more than 500 ps under isotropicisothermal - isobaric ensemble (  N-p-T  ) conditions, to its equi-librium density at 298 K and 0.1 MPa. The final size of thebox allowed a cutoff distance of 1.6 nm. For all compounds,the vapor phase was modeled  V  ia  isolated molecules in thecanonical (  N  - V  - T  ) ensemble at 298 K. Since the statistics arepoor due to the small number of atoms, each production runtook 40 ns and 20 such runs were used to calculate the averagegas-phase properties. Results and Discussion The standard atomic masses recommended by the IUPACCommission in 2005 81 were used in the calculation of all molarthermochemical quantities. Molecular and Crystal Structure Determination.  The bonddistances and angles obtained by single-crystal X-ray diffractionfor Fe( η 5 -C 5 H 4 CH 3 ) 2  at 293 K and Fe[( η 5 -C 5 H 5 )( η 5 -C 5 H 4 CHO)]at 150 K are given in Table 2. A comparison of some selectedgeometrical features of both compounds found in this work,with the corresponding information previously reported atdifferent temperatures, is presented in Table 3.The crystal structure of Fe( η 5 -C 5 H 4 CH 3 ) 2  at 293 K consistsof four molecules per unit cell. A perspective representation of the compound is shown in Figure 1, along with the labelingscheme used. Similarly to what has been found by Foucher etal. 79 at 173 K, the cyclopentadienyl rings are almost eclipsedand the methyl substituents are in the  cis  conformation.However, the Fe - Cp centroid  bond distances as well as the Fe - C Cp  lengths presently obtained at 293 K are somewhat smallerthan those reported at 173 K: 1.6447 Å and 1.6487 Å at 293 Kvs 1.650 Å and 1.649 Å at 173 K, respectively. This effect wasalso observed by Seiler and Dunitz 82 for ferrocene structuresdetermined at different temperatures. The two C Cp - C methyl  bonddistances in the present structure are fairly different (1.474 Åand 1.530 Å) to better accommodate the bulky methyl groups.This difference is also present, although to a less extent inFoucher’s structure (1.491 Å and 1.501 Å). The larger asym-metry of the C Cp - C methyl  bond distances at 293 K is probablydue to the increase of the thermal motion of the atoms with thetemperature. The crystal of 1,1 ′ -dimethylferrocene is a van derWaals crystal where specific highly directional, intermolecularinteractions are absent.The ferrocenecarboxaldehyde compound is enantiomericallypure and crystallizes in the chiral space group  P 2 1 2 1 2 1 . As shownin Figure 2, the cyclopentadienyl rings have an almost eclipsedconformation. Analogously to what has been found in this workfor Fe( η 5 -C 5 H 4 CH 3 ) 2  and by Seiler and Dunitz 82 for ferrocene,the structure of ferrocenecarboxaldehyde obtained here at 150K exhibits longer Fe - Cp centroid  and Fe - C Cp  bond distances thanthat reported by Daniel et al. 83 at room temperature (Table 3).The CHO substituent is almost coplanar with the Cp ring (4.6 ° ),thus allowing conjugation of the  ππ  -electron systems of theC d O bond and of the aromatic cyclopentadienyl ring. This isalso observed in the published room-temperature structure. 83 Theexistence of CO - Cp conjugation is supported by the C(6) - C(11) bond length of 1.444 Å, which is between typical valuesfor single and double C(6) - C(11) bond distances (1.54 Å and1.40 Å respectively). The C d O bond length is 1.042 Å and theC(6) - C(11) - O(11) bond angle is 142.5 ° . In the crystal packingthe CO group forms two intermolecular interactions, which areapproximately of the same length: C(5) - H(5) ‚‚‚ O(11) 2.713-(7) Å and C(8) - H(8) ‚‚‚ O(18) 2.779(7) Å. This conclusion isbased on the criterion that the sum of the van der Waals radiiof H and O is the higher limit for the existence of an H ‚‚‚ Ointeraction. 57 The C(5) - H(5) ‚‚‚ O(11) interaction generates achain of molecules along the  a -axis (Figure 3a) while the C(8) - H(8) ‚‚‚ O(18) interaction produces another chain along the  b -axis(Figure 3b). These two supramolecular motifs are connectedmaking a three-dimensional network. TABLE 2: Bond Lengths (Å) and Angles (deg) for1,1 ′ -Dimethylferrocene and Ferrocenecarboxaldehyde Fe( η 5 -C 5 H 4 CH 3 ) 2 Fe[( η 5 -C 5 H 5 )-( η 5 -C 5 H 4 CHO)]Fe(1) - Cp2 1.6447(10) 1.6380(11)Fe(1) - Cp1 1.6487(10) 1.6523(11)Fe(1) - C(Cp) 2.011(7) - 2.062(7) 2.007(6) - 2.049(5)C(1) - C(2) 1.386(10) 1.411(11)C(3) - C(2) 1.398(10) 1.390(9)C(4) - C(3) 1.440(10) 1.366(8)C(4) - C(5) 1.411(11) 1.390(9)C(1) - C(5) 1.436(9) 1.400(11)C(6) - C(7) 1.407(11) 1.402(10)C(7) - C(8) 1.396(12) 1.390(12)C(8) - C(9) 1.403(11) 1.404(13)C(10) - C(9) 1.426(9) 1.350(12)C(6) - C(10) 1.425(10) 1.382(9)C(6) - C(11) 1.444(14)O(11) - C(11) 1.042(10)C(5) - C(51) 1.474(9)C(10) - C(101) 1.530(10)Cp(1) - Fe(1) - Cp(2) 178.47(6) 178.86(5)O(11) - C(11) - C(6) 142.5(17) Iron Metalocenes  J. Phys. Chem. A, Vol. 112, No. 13, 2008   2981
Related Search
Similar documents
View more
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks