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Molecular ordering by halide–halide interactions in dimolybdenum p-halobenzoates
Inorganica Chimica Acta 424 (2015) 300–307
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Molecular ordering by halide–halide interactions in dimolybdenum p-halobenzoates Malcolm H. Chisholm ⇑, Christopher B. Durr, Thomas F. Spilker, Philip J. Young Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, United States
a r t i c l e
i n f o
Article history: Received 2 July 2014 Received in revised form 12 August 2014 Accepted 16 August 2014 Available online 29 August 2014 SI: Metal-metal bonded compounds Keywords: X-ray crystal structure Metal–metal bonding Dimolybdenum complexes
a b s t r a c t A series of compounds of the form Mo2(O2C-C6H4-X)4, 1-X, and trans-Mo2(TiPB)2(O2C-C6H4-X)2, 2-X, have been prepared where X = F, Cl, Br, and I and TiPB = 2,4,6-triisopropylbenzoate. The compounds 1-X (X = F, Cl) and 2-X (X = F, Cl, Br, and I) have been structurally characterized by single crystal X-ray crystallography, some of which are shown to form extended chains in the solid state due to the formation of halide– halide intermolecular interactions. Both families of compounds have been examined by electronic absorption and emission spectroscopy and the lifetimes of the singlet and triplet lifetimes have been determined. S1 lifetimes are 5–8 ps and T1 lifetimes are 50–80 ls. The heavy atom halogen appears to have little effect on the S1 lifetimes. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
2. Results and discussion
Dimolybdenum carboxylates, Mo2(O2CR)4 are amongst the most numerous of quadruply bonded complexes [1]. They are easily prepared from the reaction between Mo(CO)6 and the appropriate carboxylic acid in a refluxing solvent such as dichlorobenzene [2,3]. The carboxylate ligands are substitutionally labile and this has allowed the formation of linked dinuclear species including molecular triangles, squares and higher order polygons [4–6]. The Mo4+ 2 units have the ability to bind solvent molecules such as THF or MeCN along the MM axis. These appear to be weak bonds as evidenced by the relatively long Mo–O and Mo–N distances 0 2.5 Å A [1]. The propensity for this axial ligation also manifests itself when such donor solvents are not present by the formation of intermolecular Mo2 O interactions and this leads to the Mo2(O2CR)4 compounds forming laddered structures of the type depicted in Fig. 1, specifically seen in compounds bearing benzoate ligands [7]. In this paper, we describe the preparations and solid state molecular structures of a series of para-halobenzoates bound to the quadruply bonded Mo4+ 2 unit that show an alternate form of packing in the solid-state due to the formation of weak halidehalide interactions. We also report on the photophysical properties of these complexes and show the chosen halogen affects the energy of the 1MLCT states but not does significantly affect the lifetimes of these states.
2.1. Synthesis
⇑ Corresponding author. E-mail address: [email protected] (M.H. Chisholm). http://dx.doi.org/10.1016/j.ica.2014.08.016 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
The series of homoleptic compounds 1-X (X = F, Cl, Br and I) were prepared from the reactions between Mo(CO)6 and the respective halobenzoic acid in refluxing dichlorobenzene. The heteroleptic series of compounds trans-Mo2(TiPB)2(O2C-C6H4-X)2, 2-X (X = F, Cl, Br and I), termed bis-bis compounds, were prepared from the reactions between Mo2(TiPB)4 and the respective halobenzoic acid in toluene [8] (see Scheme 1). The new compounds are yellow-orange in the solid state. All compounds were soluble in THF and sparingly soluble in toluene. Compounds of the type 1-X and 2-X showed 1H NMR data consistent with their formulations and molecular ions by MALDI-TOF mass spectra. The details of characterization are given in the experimental section. 2.2. Electronic absorption and steady state emission spectra The spectra recorded for the homoleptic compounds 1-X and the trans-substituted complexes 2-X in THF at room temperature are shown in Fig. 2. The homoleptic compounds 1-X show two absorption bands, one corresponding to a ligand based p–p⁄ transition in the ultraviolet and the other a fully allowed metal-toligand charge transfer (MLCT) transition from the Mo2d to the ligand-p⁄ in the visible. Both of these transitions decrease energetically upon moving down the halide series from F to I. The bis-bis compounds 2-X also show the p–p⁄ and MLCT absorption bands
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Fig. 1. Molecular ordering by Mo2 O interactions in Mo2(O-C6H5)4.
similar to the homoleptic 1-X compounds. Since the compounds possess an additional carboxylate ligand, namely TiPB, a second MLCT transition from the Mo2d to the TiPB-CO2-p⁄ is also present. This occurs at similar wavelength for all compounds at 330 nm. Also, for comparison, we note 1-F and 2-F show almost identical spectral features to their simple benzoate counterparts [8]. Upon irradiation into the MLCT absorption bands, the compounds also show very weak fluorescence from the S1 states as shown in Fig. 3. These emission spectra show the expected trends based on the absorption spectra. The compounds also show phosphorescence from the T1 dd⁄ state which is centered around 1100 nm which is typical of dimetal tetracarboxylates that increases notably in intensity upon cooling to 77 K [9]. The nearIR emission spectra can be seen in the Supporting information.
halogen atoms on the excited state lifetimes. Presumably, the heavier iodine atom could better facilitate intersystem crossing to the triplet state thus leading to a shortened singlet state lifetime. The compounds showed weak features in the UV–Vis region by femtosecond transient absorption spectroscopy (fs TA), however, these features were more pronounced in the femotosecond time resolved infrared spectroscopy (fs TRIR) studies, particularly the region associated with the m(CO2) stretch. This method was therefore chosen to determine the lifetimes of the S1 states which are listed in Table 1. A representative spectrum of 2-Br is shown in Fig. 4. All of the compounds show similar lifetimes for the S1 states, ranging from 5 to 8 picoseconds (ps). We note that 2-I has the shortest S1 lifetime and 2-F is the longest but the difference is marginal. The lifetimes of the T1 states were determined by nanosecond (ns) transient absorption spectroscopy and these data are also listed in Table 1 where it can be seen that the T1 values are on the order of 50–80 ls. These values are typical of other dimolybdenum tetracarboxylates which have been studied thus far and are characteristic of 3MoMo dd⁄ T1 states [2,10,11]. Kinetic plots and errors associated with the lifetimes are given in the Supporting information.
2.3. Ultrafast spectroscopy
2.4. Solid state molecular structures
Ultrafast spectroscopy studies were performed on the heteroleptic (2-X) compounds in order to study the effect of the different
A summary of the crystallographic data parameters for homoleptic compounds 1-X can be seen in Table 2, and those for the trans
Scheme 1. Synthesis of 4-halobenzoic acid supported Mo2 homoleptic and bis-bis complexes, where X = F, Cl, Br, and I.
Fig. 2. Electronic absorption spectrum of families 1-X (left) and 2-X (right) taken in THF at room temperature.
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Fig. 3. Fluorescence spectra of families 1-X (left) and 2-X (right) taken in THF at room temperature upon excitation into the MLCT absorption band.
Table 1 Lifetimes of S1 and T1 excited states of compounds 1-X and 2-X. Compound
S1
T1
1-F 1-Cl 1-Br 1-I 2-F 2-Cl 2-Br 2-I
– – – – 7.8 ps 5.4 ps 6.7 ps 4.1 ps
53 ls 55 ls 58 ls 56 ls 66 ls 62 ls 64 ls 75 ls
compounds 2-X in Table 3. In total six structural determinations have been carried out. An ORTEP drawing of each structure can be seen in Fig. 5. It should be noted that the homoleptic compounds containing iodo- and bromo- benzoates failed to yield crystals suitable for our single crystal X-ray analysis. After numerous attempts, recrystallization from layering of THF and hexanes yielded very thin plates and fiber like rods. The fluoro and chlorobenzoates however did yield suitable crystals. In the solid state the fluoro derivate exists as a discrete molecular unit axially coordinated by THF. In contrast the chloro- derivative which is also axially coordinated by THF forms an infinite chain structure in the solid state due to
the formation of weak molecular Cl–Cl interactions as can be seen in Fig. 6. Each Mo2 unit forms four halogen halogen bonds and the Cl–Cl distances are 3.30 Å. Of the trans substituted series, the compounds involving X = Br and I, show similar halogen–halogen interactions in the solid state. This interaction again leads to extended chains. The solid state extended structure of 2-I is seen in Fig. 6 and that of the bromo in Fig. 7. In all of the structures the TiPB moieties are twisted 90° with respect to their attending carboxylates while the halo benzoates are planer to their carboxylates, which has been seen in related compounds. The I–I distance is 3.80 Å while the Br–Br distances are 3.59 Å. It is also important to note that the manner in which these halogens interact is different in each case. In the case of I–I the halogens slip to the side of one another, along the direction of the metal–metal axis, while in the bromo case they slip vertically, along the direction of the TiPB moiety. These extended structures can be seen in Figs. 7 and 8. The chlorobenzoate exists in the solid state as a discrete molecular species with, like all the other molecules, axial coordination of THF. However, it is interesting to note that it does not contain Cl–Cl interactions as was seen in the homoleptic chlorobenzoate. The fluorobenzoate also does not show F–F interactions but rather shows evidence of p–p stacking to again form an extended chain as
Fig. 4. Femtosecond TRIR spectra of 2-Br in THF at RT, kexc = 350 nm.
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a b
Compound
1-F
1-Cl
Chemical formula Formula weight T (K) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalcd (Mg/m3) Crystal size (mm) h range for data collection (°) l (Mo, Ka) (mm1) Reflections collected Unique reflections (Rint) Data completeness to (h) Data/restraints/parameters R1a (%) (all data) wR2b (%) (all data) Goodness-of-fit (GOF) on F2 Largest difference in peak and hole (e Å3)
C36H32F4Mo2O10 892.49 150(2) monoclinic, P21/c 9.4977(1) 18.0339(4) 11.0316(2)
C36H32Cl4Mo2O10 958.29 150(2) triclinic, P 1 6.7473(1) 11.6194(2) 12.1291(3) 95.576(1) 99.128(1) 100.377(1) 915.74(3) 1 1.738 0.27 0.12 0.12 1.715–27.472 1.034 28 066 4201 (0.030) 100.0% (25.242) 4201/0/235 2.74 (3.67) 7.29 (9.60) 1.276 0.851 and 1.032
110.952(1) 1764.57(5) 2 1.680 0.38 0.19 0.15 2.259–27.460 0.789 33 362 4038 (0.030) 100.0% (25.242) 4038/0/235 3.27 (4.43) 8.74 (10.09) 1.165 0.946 and 0.670
P P ||Fo| |Fc||/ |Fo| 100. hP i P wR2 = w(F2o F2c )2/ (w|Fo|2)2 1/2 100. R1 =
shown in Fig. 9. The Mo2(O2C)4 cores are typical of those reported previously [1]. Previously, crystal packing in the M2 tetracarboxylates has been limited to Mo O interactions between adjacent M2 cores and carboxylates or p–p stacking [9] between p-conjugated ligands. The halogen–halogen interaction allows for a new avenue of templates M2(O2CR)4 in the solid state. To this point, halogen–halogen interactions have been seen in a wide range of organic systems and have been employed in crystal engineering [12–19]. In general these weak halogen–halogen interaction favor the heavier elements I–I > Br–Br > Cl–Cl and in organic systems have been classified by their respective C–X X angles. Type 1 compounds
have C–X X angles that are essentially equal as is seen for the bis-bis iodo- and bromo- para-benzoate. However, for the homoleptic para-chlorobenzoate we see an example of a type 2 structure where one C–Cl Cl angle is essentially linear while the other is 90° [20]. To further illustrate this point we summarize the C–X X angles in Table 4. 3. Concluding remarks Two families of halogenated Mo2 quadruply bonded compounds have been synthesized and characterized. The MLCT absorption and emission spectra show a dependence on the halo-
Table 3 Select crystallographic parameters for homoleptic compounds 2 – (F-I).
a b
Compound
2-F
2-Cl
2-Br
2-I
Chemical formula Formula weight T (K) Space group a (Å) b(Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalcd (Mg/m3) Crystal size (mm) h range for data collection (°) l (Mo, Ka) (mm1) Reflections collected Unique reflections (Rint) Data completeness to (h) Data/restraints/parameters R1a (%) (all data) wR2b (%) (all data) Goodness-of-fit (GOF) on F2 Largest difference in peak and hole (e Å3)
C54H70F2Mo2O10 1108.98 150(2) monoclinic, P21/c 10.1027(2) 15.2966(4) 17.1975(4)
C54H70Cl2Mo2O10 1141.88 152(2) monoclinic, P21/c 10.5454(3) 28.4540(9) 10.0650(3)
94.985(2)
115.025(1)
2647.60(11) 2 1.391 0.38 0.38 0.23 2.378–27.454 0.536 46 777 6037 (0.049) 99.9% (25.242)] 6037/15/307 3.65 (5.25) 8.85 (9.98) 1.079 0.736 and 0.505
2736.57(14) 2 1.386 0.38 0.23 0.19 1.431–27.438 0.610 40 716 6237 (0.051) 100.0% (25.242) 6237/0/307 4.41 (7.12) 10.91 (12.65) 1.101 1.534 and 0.595
C54H70Br2Mo2O10 1230.80 150(2) triclinic, P 1 10.0697(2) 10.5101(2) 14.8323(2) 73.389(1) 80.287(1) 64.104(1) 1351.45(4) 1 1.512 0.27 0.19 0.15 1.435–27.475 1.997 35 192 6194 (0.048) 99.9% (25.242) 6194/0/307 3.76 (6.17) 9.0 (11.9) 1.12 0.90 and 1.47
C54H70I2Mo2O10 1324.78 150(2) triclinic, P 1 10.0917(3) 10.4630(2) 14.7965(4) 76.668(2) 86.366(1) 65.537(2) 1382.87(7) 1 1.591 0.31 0.27 0.19 1.415–27.426 1.623 35 285 6286 (0.041) 100.0% (25.242) 6286/0/307 3.81 (6.35) 9.41 (12.77) 1.116 2.111 and 0.969
P P ||Fo| |Fc||/ |Fo| 100. hP i P wR2 = w(F2o F2c )2/ (w|Fo|2)2 1/2 100. R1 =
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Fig. 5. ORTEP drawings of 1 (F,Cl) and 2 (F–I) drawn at 50% probability. Solvent and hydrogen atoms removed for clarity.
gen shifting to lower energy with a progression down the group. We observed minimal change in the excited state lifetimes as the halogen was varied. This implies that the S1 and T1 lifetimes are dictated primarily by the heavy atom effect of the Mo2 core rather than the ancillary halogens. In the solid state we observed that the packing of the molecules was contingent upon the identity and quantity of the attending halobenzoate. The trans compounds containing Br and I were shown to assemble in a linear, 1-D type arrangement, facilitated by halogen– halogen interactions. This interaction was not seen, however, in the more electronegative ligands containing F and Cl indicating a weaker halogen–halogen interaction and, instead, favoring pp stack ing. Increasing the number of attending halogens however did afford 1-D packing as the Cl containing homoleptic compound was able to bind through all four arms. This interaction, while subtle, could facilitate crystal engineering of Mo2(O2CR)4 compounds in the future.
3. Experimental 3.1. General methods All solvent were dried and distilled from appropriate agents and stores over 4 Å molecular sieves in Kontes top flasks. All reactions and preparations were perform under UHP argon using standard Schlenk and glovebox techniques. Mo(CO)6 was purchased from Alfa Aesar and used as received. The halogenated benzoic acids were purchased from Sigma Aldrich Chemical Co. and used as received. Mo2(TiPB)4 was prepared according to a previously published procedure [3]. NMR spectra were taken a on a 400 MHz Bruker DPX Advance 400 spectrometer. All 1H NMR chemical shifts are in parts per million (PPM) relative to the protio impurity at, 2.50 for DMSO-d6 and 3.58 for THF-d8.
Fig. 6. Cl–Cl laddering of the homoleptic compound 1-Cl.
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Fig. 7. Top down and side on view showing the Br–Br interactions in 2-Br.
Fig. 8. Top down and side on view showing the I–I interactions in 2-I.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were obtained on a Bruker Microflex mass spectrometer. Dithranol was used as a matrix. Samples were prepared by adding a solution of the matrix to the solid sample, which was then spotted for analysis. An internal standard was employed to calibrate the observed peaks. 3.2. Electronic absorption spectra UV–Vis–NIR electronic spectra in THF solutions were measured at room temperature using a Perkin–Elmer Lambda 900 spectrometer using 1 cm 1 cm quartz cuvettes sealed with Kontes tops. 3.3. Steady state emission spectra The steady-state luminescence spectra between 350 and 800 nm were acquired on a SPEX Fluoromax-2 spectrofluorometer. The spectra were measured in THF at room temperature and in 2-methyltetrahydrofuran at 77 K. Samples were excited into their MLCT bands. The steady-state near-IR luminescence spectra were
taken on a home-built instrument utilizing a germanium detector. All measurements were recorded in 2-methyltetrahydrofuran using an excitation wavelength of 405 nm. 3.4. Time-resolved measurements Time-resolved infrared21 spectroscopy experiments were performed with a Ti:sapphire and regenerative amplifier combination (1 kHz, 300 fs fwhm) that has been previously described. Samples of 2-I, 2-Br, 2-Cl, and 2-F were prepared in THF with an absorbance of 1 at kmax. Solutions were sealed in a PerkinElmer semidemountable cell with a 0.1 mm Teflon spacer between 4 mm CaF2 windows. Compounds 2-I, 2-Br, 2-Cl, and 2-F were excited at 350 nm with a laser power of 1 lJ. In the ns TA experiment, samples were prepared in a 1 cm quartz cuvette with Kontes top with absorbance 0.1–0.3 and excitation power at the sample of 100 mW [22]. All samples were excited at a wavelength of 355 nm. Kinetics for the time-resolved data were fit to a sum of expoP nentials, S(t) = i Ai exp(1/si)+ C, where Ai is the amplitude, sI is the lifetime, and C is an offset, in Igor Pro 6.0 or SigmaPlot
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Fig. 9. Top down and side on view of the p p stacking seen in 2-F.
Table 4 A summary of solid state interactions from 1 (F,Cl) and 2 (F – I) including the type of halogen–halogen interaction. Compound
C–X X0 angle
C0 –X0 X angle
Interaction
1-F 1-Cl 2-F 2-Cl 2-Br 2-I
– 176.2° – – 162.8° 146.8°
– 85.1° – – 162.8° 146.8°
N/A type 2 halogen–halogen p–p stacking N/A type 1 halogen–halogen type 1 halogen–halogen
12.0. Standard errors of the exponential fits are given as the error bars of the lifetimes. For the TRIR experiments, the transients were fit to Gaussian functions and the peak position was plotted against the delay times. General Synthesis of 1-X. Mo(CO)6 and two equivalents of the respective carboxylic acid were placed into a Schlenk flask and 4:1 o-dichlorobenzene:THF mixture [10–15 mL total]. The mixture was heated to reflux [140 °C] for 48 h. Upon cooling, the THF was removed under vacuum and the product precipitated from solution. The desired product was isolated as a microcrystalline powder by filtration and washing with hexanes [3 15 mL]. General Synthesis of 2-X. Mo2(TiPB)4 and two equivalents of the desired carboxylic acid were combined in a Schlenk flask and dissolved in toluene [10–15 mL]. The reaction mixed at room temperature for 48 h where a precipitate formed. The desired product was isolated by filtration as a powder and was further purified by washings with hexanes [3 15 mL].
1-F. Mo(CO)6 [250 mg, 0.95 mmol] and 4-fluorobenzoic acid [268 mg, 1.91 mmol] produced Mo2(PhF)4 [345 mg, 97%]. NMR (DMSO-d6): dH (400 MHz) 8.23 (dd, 8H, JHH = 8.4 Hz, JHF = 5.3 Hz), 7.38 (t, 8H, JHH = 8.8 Hz, JHF = 8.8 Hz). MALDI-TOF MS: C28H16F4Mo2O8 Calculated: 751.9, Found: 747.0. 1-Cl. Mo(CO)6 [250 mg, 0.95 mmol] and 4-chlorobenzoic acid [304 mg, 1.95 mmol] produced Mo2(PhCl)4 [370 mg, 96%]. NMR (DMSO-d6): dH (400 MHz) 8.16 (d, 8H, JHH = 8.6 Hz), 7.60 (d, 8H, JHH = 8.6 Hz). MALDI-TOF MS: C28H16Cl4Mo2O8 Calculated: 815.8, Found: 812.9. 1-Br. Mo(CO)6 [250 mg, 0.95 mmol] and 4-bromobenzoic acid [398 mg, 1.98 mmol] produced Mo2(PhBr)4 [410 mg, 87%]. NMR (THF-d8): dH (400 MHz) 8.13 (d, 8H, JHH = 8.5 Hz), 7.63 (d, 8H, JHH = 8.5 Hz). MALDI-TOF MS: C28H16Br4Mo2O8 Calculated: 991.6, Found: 990.9. 1-I. Mo(CO)6 [250 mg, 0.95 mmol] and 4-iodobenzoic acid [470 mg, 1.90 mmol] produced Mo2(PhI)4 [510 mg, 91%]. NMR (THF-d8): dH (400 MHz) 7.96 (d, 8H, JHH = 8.0 Hz), 7.74 (d, 8H, JHH = 8.2 Hz). MALDI-TOF MS: C28H16I4Mo2O8 Calculated: 1183.5, Found: 1179.9. 2-F. Mo2(TiPB)4 [100 mg, 0.085 mmol] and 4-fluorobenzoic acid [24 mg, 0.171 mmol] produced Mo2(TiPB)2(PhF)2 [55 mg, 67%]. NMR (THF-d8): dH (400 MHz) 8.40 (dd, 4H, J = 8.4, 5.6 Hz), 7.31 (t, 4H, J = 5.6 Hz) 7.00 (s, 4H), 3.03 (sep, 4H, JHH = 6.9 Hz), 2.87 (sep, 2H, JHH = 6.9 Hz), 1.23 (d, 12H, JHH = 6.9 Hz), 1.03 (d, 24H, JHH = 6.9 Hz). MALDI-TOF MS: C46H54F2Mo2O8 Calculated: 968.2, Found: 965.2. 2-Cl. Mo2(TiPB)4 [200 mg, 0.17 mmol] and 4-chlorobenzoic acid [52.8 mg, 0.34 mmol] produced Mo2(TiPB)2(PhCl)2 [132 mg, 78%]. NMR (DMSO-d6): dH (400 MHz) 8.34 (d, 4H, JHH = 8.5 Hz), 7.60 (d,
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4H, JHH = 8.5 Hz), 7.00 (s, 4H), 3.02 (sep, 4H, JHH = 6.8 Hz), 2.87 (sep, 2H, JHH = 6.8 Hz), 1.23 (d, 12H, JHH = 6.8 Hz), 1.03 (d, 24H, JHH = 7.0 Hz). MALDI-TOF MS: C46H54Cl2Mo2O8 Calculated: 1000.0 Found: 997.6. 2-Br. Mo2(TiPB)4 [600 mg, 0.51 mmol] and 4-bromobenzoic acid [195 mg, 0.97 mmol] produced Mo2(TiPB)2(PhBr)2 [483 mg, 87%]. NMR (DMSO-d6): dH (400 MHz) 8.26 (d, 4H, JHH = 8.6 Hz), 7.77 (d, 4H, JHH = 8.6 Hz) 7.01 (s, 4H), 3.02 (sep, 4H, JHH = 6.6 Hz), 2.88 (sep, 4H, JHH = 6.6 Hz), 1.24 (d, 12H, JHH = 6.6 Hz), 1.04 (d, 24H, JHH = 6.6 Hz). MALDI-TOF MS: C46H54Br2Mo2O8 Calculated: 1088.0 Found: 1085.7. 2-I. Mo2(TiPB)4 [200 mg, 0.17 mmol] and 4-iodobenzoic acid [84 mg, 0.34 mmol] produced Mo2(TiPB)2(PhI)2 [155 mg, 75%]. NMR (THF-d8): dH (400 MHz) 8.09 (d, 4H, JHH = 8.4 Hz), 7.97 (d, 4H, JHH = 8.4 Hz), 7.00 (s, 4H), 3.01 (sep, 4H, JHH = 7.5 Hz), 2.87 (sep, 6H, JHH = 7.0 Hz), 1.23 (d, 12H, JHH = 7.0 Hz), 1.03 (d, 24H, JHH = 7.0 Hz). MALDI-TOF MS: C46H54I2Mo2O8: Calculated: 1184.0, Found: 1181.5. 3.5. Single crystal X-ray diffraction Single crystals of 1 – (F, Cl) and 2 – (F-I) were isolated and handled under a pool of fluorinated oil. Examination of the diffraction pattern was done on a Nonius Kappa CCD diffractometer with Mo Ka radiation. All work was conducted at 150 K using an Oxford Cryosystems Cryostream Cooler. Data integration was performed with Denzo, and scaling and merging of the data was done with Scalepack [23]. The structures were solved by the direct methods program in SHELXS-13 [24]. Full-matrix least-squares refinements based on F2 were performed in SHELXL-13 [24], as incorporated in the WinGX package [25], For each methyl group, the hydrogen atoms were added at calculated positions using a riding model with U(H) = 1.5Ueq (bonded carbon atom). The rest of the hydrogen atoms were included in the model at calculated positions using a riding model with U(H) = 1.2Ueq (bonded atom). Neutral atom scattering factors were used and include terms for anomalous dispersion [26]. Acknowledgements The authors would like to thank the National Science Foundation for funding this research on grant numbers 0957191 and 1266298. We also acknowledge Professor Claudia Turro for use of instrumentation and The Ohio State University Center for Chemical and Biophysical Dynamics for laser systems.
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Appendix A. Supplementary material CCDC 1011284–1011289 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http:// dx.doi.org/10.1016/j.ica.2014.08.016. References [1] F. Albert Cotton, R.A. Walton, C.A. Murillo, Multiple bonds between Metal Atoms, third ed., Springer Science and Business Media, Inc., 2005. [2] S.E. Brown-Xu, M.H. Chisholm, C.B. Durr, T.F. Spilker, J. Phys. Chem. A 117 (2013) 13893. [3] F.A. Cotton, L.M. Daniels, E.A. Hillard, C.A. Murillo, Inorg. Chem. 41 (2002) 1639. [4] M.H. Chisholm, N.J. Patmore, C.R. Reed, N. Singh, Inorg. Chem. 49 (2010) 7116. [5] F.A. Cotton, C.A. Murillo, R. Yu, Dalton Trans. (2006) 3900. [6] F.A. Cotton, C. Lin, C.A. Murillo, Acc. Chem. Res. 34 (2001) 759. [7] F.A. Cotton, M. Extine, L.D. Gage, Inorg. Chem. 17 (1978) 172. [8] S.E. Brown-Xu, M.H. Chisholm, C.B. Durr, T.F. Spilker, P.J. Young, Dalton Trans. 42 (2013) 14491. [9] G.T. Burdzinski, M.H. Chisholm, P.-T. Chou, Y.-H. Chou, F. Feil, J.C. Gallucci, Y. Ghosh, T.L. Gustafson, M.-L. Ho, Y. Liu, R. Ramnauth, C. Turro, Proc. Natl. Acad. Sci. 105 (2008) 15247. [10] S.E. Brown-Xu, M.H. Chisholm, C.B. Durr, T.F. Spilker, J. Am. Chem. Soc. 135 (2013) 8254. [11] S.E. Brown-Xu, M.H. Chisholm, C.B. Durr, T.L. Gustafson, T.F. Spilker, J. Phys. Chem. A 117 (2013) 5997. [12] F.F. Awwadi, R.D. Willett, K.A. Peterson, B. Twamley, Chem.-Eur. J. 12 (2006) 8952. [13] E. Corradi, S.V. Meille, M.T. Messina, P. Metrangolo, G. Resnati, Angew. Chem., Int. Ed. 39 (2000) 1782. [14] M. Fourmigué, Curr. Opin. Solid State Mater. Sci. 13 (2009) 36. [15] P. Metrangolo, H. Neukirch, T. Pilati, G. Resnati, Acc. Chem. Res. 38 (2005) 386. [16] V.R. Pedireddi, D.S. Reddy, B.S. Goud, D.C. Craig, A.D. Rae, G.R. Desiraju, J. Chem. Soc., Perkin Trans. 2 (1994) 2353. [17] N. Ramasubbu, R. Parthasarathy, P. Murray-Rust, J. Am. Chem. Soc. 108 (1986) 4308. [18] T.T.T. Bui, S. Dahaoui, C. Lecomte, G.R. Desiraju, E. Espinosa, Angew. Chem., Int. Ed. 48 (2009) 3838. [19] G.R. Desiraju, R. Parthasarathy, J. Am. Chem. Soc. 111 (1989) 8725. [20] M.B. Andrews, C.L. Cahill, Dalton Trans. 41 (2012) 3911. [21] J. Wang, G. Burdzinski, J. Kubicki, M.S. Platz, J. Am. Chem. Soc. 130 (2008) 11195. [22] M.J. Byrnes, M.H. Chisholm, J.A. Gallucci, Y. Liu, R. Ramnauth, C. Turro, J. Am. Chem. Soc. 127 (2005) 17343. [23] Z. Otwinowski, Minor, W. Methods in Enzymology, vol. 276: Macromolecular Crystallography, Part A, Academic Press, 1997. [24] G. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112. [25] L. Farrugia, J. Appl. Crystallogr. 32 (1999) 837. [26] International Tables for Crystallography, volume C, Kluwer Academic Publishers, Dordrecht, 1992.
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Molecular ordering by halide–halide interactions in dimolybdenum p-halobenzoates Malcolm H. Chisholm ⇑, Christopher B. Durr, Thomas F. Spilker, Philip J. Young Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, United States
a r t i c l e
i n f o
Article history: Received 2 July 2014 Received in revised form 12 August 2014 Accepted 16 August 2014 Available online 29 August 2014 SI: Metal-metal bonded compounds Keywords: X-ray crystal structure Metal–metal bonding Dimolybdenum complexes
a b s t r a c t A series of compounds of the form Mo2(O2C-C6H4-X)4, 1-X, and trans-Mo2(TiPB)2(O2C-C6H4-X)2, 2-X, have been prepared where X = F, Cl, Br, and I and TiPB = 2,4,6-triisopropylbenzoate. The compounds 1-X (X = F, Cl) and 2-X (X = F, Cl, Br, and I) have been structurally characterized by single crystal X-ray crystallography, some of which are shown to form extended chains in the solid state due to the formation of halide– halide intermolecular interactions. Both families of compounds have been examined by electronic absorption and emission spectroscopy and the lifetimes of the singlet and triplet lifetimes have been determined. S1 lifetimes are 5–8 ps and T1 lifetimes are 50–80 ls. The heavy atom halogen appears to have little effect on the S1 lifetimes. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
2. Results and discussion
Dimolybdenum carboxylates, Mo2(O2CR)4 are amongst the most numerous of quadruply bonded complexes [1]. They are easily prepared from the reaction between Mo(CO)6 and the appropriate carboxylic acid in a refluxing solvent such as dichlorobenzene [2,3]. The carboxylate ligands are substitutionally labile and this has allowed the formation of linked dinuclear species including molecular triangles, squares and higher order polygons [4–6]. The Mo4+ 2 units have the ability to bind solvent molecules such as THF or MeCN along the MM axis. These appear to be weak bonds as evidenced by the relatively long Mo–O and Mo–N distances 0 2.5 Å A [1]. The propensity for this axial ligation also manifests itself when such donor solvents are not present by the formation of intermolecular Mo2 O interactions and this leads to the Mo2(O2CR)4 compounds forming laddered structures of the type depicted in Fig. 1, specifically seen in compounds bearing benzoate ligands [7]. In this paper, we describe the preparations and solid state molecular structures of a series of para-halobenzoates bound to the quadruply bonded Mo4+ 2 unit that show an alternate form of packing in the solid-state due to the formation of weak halidehalide interactions. We also report on the photophysical properties of these complexes and show the chosen halogen affects the energy of the 1MLCT states but not does significantly affect the lifetimes of these states.
2.1. Synthesis
⇑ Corresponding author. E-mail address: [email protected] (M.H. Chisholm). http://dx.doi.org/10.1016/j.ica.2014.08.016 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
The series of homoleptic compounds 1-X (X = F, Cl, Br and I) were prepared from the reactions between Mo(CO)6 and the respective halobenzoic acid in refluxing dichlorobenzene. The heteroleptic series of compounds trans-Mo2(TiPB)2(O2C-C6H4-X)2, 2-X (X = F, Cl, Br and I), termed bis-bis compounds, were prepared from the reactions between Mo2(TiPB)4 and the respective halobenzoic acid in toluene [8] (see Scheme 1). The new compounds are yellow-orange in the solid state. All compounds were soluble in THF and sparingly soluble in toluene. Compounds of the type 1-X and 2-X showed 1H NMR data consistent with their formulations and molecular ions by MALDI-TOF mass spectra. The details of characterization are given in the experimental section. 2.2. Electronic absorption and steady state emission spectra The spectra recorded for the homoleptic compounds 1-X and the trans-substituted complexes 2-X in THF at room temperature are shown in Fig. 2. The homoleptic compounds 1-X show two absorption bands, one corresponding to a ligand based p–p⁄ transition in the ultraviolet and the other a fully allowed metal-toligand charge transfer (MLCT) transition from the Mo2d to the ligand-p⁄ in the visible. Both of these transitions decrease energetically upon moving down the halide series from F to I. The bis-bis compounds 2-X also show the p–p⁄ and MLCT absorption bands
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Fig. 1. Molecular ordering by Mo2 O interactions in Mo2(O-C6H5)4.
similar to the homoleptic 1-X compounds. Since the compounds possess an additional carboxylate ligand, namely TiPB, a second MLCT transition from the Mo2d to the TiPB-CO2-p⁄ is also present. This occurs at similar wavelength for all compounds at 330 nm. Also, for comparison, we note 1-F and 2-F show almost identical spectral features to their simple benzoate counterparts [8]. Upon irradiation into the MLCT absorption bands, the compounds also show very weak fluorescence from the S1 states as shown in Fig. 3. These emission spectra show the expected trends based on the absorption spectra. The compounds also show phosphorescence from the T1 dd⁄ state which is centered around 1100 nm which is typical of dimetal tetracarboxylates that increases notably in intensity upon cooling to 77 K [9]. The nearIR emission spectra can be seen in the Supporting information.
halogen atoms on the excited state lifetimes. Presumably, the heavier iodine atom could better facilitate intersystem crossing to the triplet state thus leading to a shortened singlet state lifetime. The compounds showed weak features in the UV–Vis region by femtosecond transient absorption spectroscopy (fs TA), however, these features were more pronounced in the femotosecond time resolved infrared spectroscopy (fs TRIR) studies, particularly the region associated with the m(CO2) stretch. This method was therefore chosen to determine the lifetimes of the S1 states which are listed in Table 1. A representative spectrum of 2-Br is shown in Fig. 4. All of the compounds show similar lifetimes for the S1 states, ranging from 5 to 8 picoseconds (ps). We note that 2-I has the shortest S1 lifetime and 2-F is the longest but the difference is marginal. The lifetimes of the T1 states were determined by nanosecond (ns) transient absorption spectroscopy and these data are also listed in Table 1 where it can be seen that the T1 values are on the order of 50–80 ls. These values are typical of other dimolybdenum tetracarboxylates which have been studied thus far and are characteristic of 3MoMo dd⁄ T1 states [2,10,11]. Kinetic plots and errors associated with the lifetimes are given in the Supporting information.
2.3. Ultrafast spectroscopy
2.4. Solid state molecular structures
Ultrafast spectroscopy studies were performed on the heteroleptic (2-X) compounds in order to study the effect of the different
A summary of the crystallographic data parameters for homoleptic compounds 1-X can be seen in Table 2, and those for the trans
Scheme 1. Synthesis of 4-halobenzoic acid supported Mo2 homoleptic and bis-bis complexes, where X = F, Cl, Br, and I.
Fig. 2. Electronic absorption spectrum of families 1-X (left) and 2-X (right) taken in THF at room temperature.
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Fig. 3. Fluorescence spectra of families 1-X (left) and 2-X (right) taken in THF at room temperature upon excitation into the MLCT absorption band.
Table 1 Lifetimes of S1 and T1 excited states of compounds 1-X and 2-X. Compound
S1
T1
1-F 1-Cl 1-Br 1-I 2-F 2-Cl 2-Br 2-I
– – – – 7.8 ps 5.4 ps 6.7 ps 4.1 ps
53 ls 55 ls 58 ls 56 ls 66 ls 62 ls 64 ls 75 ls
compounds 2-X in Table 3. In total six structural determinations have been carried out. An ORTEP drawing of each structure can be seen in Fig. 5. It should be noted that the homoleptic compounds containing iodo- and bromo- benzoates failed to yield crystals suitable for our single crystal X-ray analysis. After numerous attempts, recrystallization from layering of THF and hexanes yielded very thin plates and fiber like rods. The fluoro and chlorobenzoates however did yield suitable crystals. In the solid state the fluoro derivate exists as a discrete molecular unit axially coordinated by THF. In contrast the chloro- derivative which is also axially coordinated by THF forms an infinite chain structure in the solid state due to
the formation of weak molecular Cl–Cl interactions as can be seen in Fig. 6. Each Mo2 unit forms four halogen halogen bonds and the Cl–Cl distances are 3.30 Å. Of the trans substituted series, the compounds involving X = Br and I, show similar halogen–halogen interactions in the solid state. This interaction again leads to extended chains. The solid state extended structure of 2-I is seen in Fig. 6 and that of the bromo in Fig. 7. In all of the structures the TiPB moieties are twisted 90° with respect to their attending carboxylates while the halo benzoates are planer to their carboxylates, which has been seen in related compounds. The I–I distance is 3.80 Å while the Br–Br distances are 3.59 Å. It is also important to note that the manner in which these halogens interact is different in each case. In the case of I–I the halogens slip to the side of one another, along the direction of the metal–metal axis, while in the bromo case they slip vertically, along the direction of the TiPB moiety. These extended structures can be seen in Figs. 7 and 8. The chlorobenzoate exists in the solid state as a discrete molecular species with, like all the other molecules, axial coordination of THF. However, it is interesting to note that it does not contain Cl–Cl interactions as was seen in the homoleptic chlorobenzoate. The fluorobenzoate also does not show F–F interactions but rather shows evidence of p–p stacking to again form an extended chain as
Fig. 4. Femtosecond TRIR spectra of 2-Br in THF at RT, kexc = 350 nm.
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a b
Compound
1-F
1-Cl
Chemical formula Formula weight T (K) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalcd (Mg/m3) Crystal size (mm) h range for data collection (°) l (Mo, Ka) (mm1) Reflections collected Unique reflections (Rint) Data completeness to (h) Data/restraints/parameters R1a (%) (all data) wR2b (%) (all data) Goodness-of-fit (GOF) on F2 Largest difference in peak and hole (e Å3)
C36H32F4Mo2O10 892.49 150(2) monoclinic, P21/c 9.4977(1) 18.0339(4) 11.0316(2)
C36H32Cl4Mo2O10 958.29 150(2) triclinic, P 1 6.7473(1) 11.6194(2) 12.1291(3) 95.576(1) 99.128(1) 100.377(1) 915.74(3) 1 1.738 0.27 0.12 0.12 1.715–27.472 1.034 28 066 4201 (0.030) 100.0% (25.242) 4201/0/235 2.74 (3.67) 7.29 (9.60) 1.276 0.851 and 1.032
110.952(1) 1764.57(5) 2 1.680 0.38 0.19 0.15 2.259–27.460 0.789 33 362 4038 (0.030) 100.0% (25.242) 4038/0/235 3.27 (4.43) 8.74 (10.09) 1.165 0.946 and 0.670
P P ||Fo| |Fc||/ |Fo| 100. hP i P wR2 = w(F2o F2c )2/ (w|Fo|2)2 1/2 100. R1 =
shown in Fig. 9. The Mo2(O2C)4 cores are typical of those reported previously [1]. Previously, crystal packing in the M2 tetracarboxylates has been limited to Mo O interactions between adjacent M2 cores and carboxylates or p–p stacking [9] between p-conjugated ligands. The halogen–halogen interaction allows for a new avenue of templates M2(O2CR)4 in the solid state. To this point, halogen–halogen interactions have been seen in a wide range of organic systems and have been employed in crystal engineering [12–19]. In general these weak halogen–halogen interaction favor the heavier elements I–I > Br–Br > Cl–Cl and in organic systems have been classified by their respective C–X X angles. Type 1 compounds
have C–X X angles that are essentially equal as is seen for the bis-bis iodo- and bromo- para-benzoate. However, for the homoleptic para-chlorobenzoate we see an example of a type 2 structure where one C–Cl Cl angle is essentially linear while the other is 90° [20]. To further illustrate this point we summarize the C–X X angles in Table 4. 3. Concluding remarks Two families of halogenated Mo2 quadruply bonded compounds have been synthesized and characterized. The MLCT absorption and emission spectra show a dependence on the halo-
Table 3 Select crystallographic parameters for homoleptic compounds 2 – (F-I).
a b
Compound
2-F
2-Cl
2-Br
2-I
Chemical formula Formula weight T (K) Space group a (Å) b(Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalcd (Mg/m3) Crystal size (mm) h range for data collection (°) l (Mo, Ka) (mm1) Reflections collected Unique reflections (Rint) Data completeness to (h) Data/restraints/parameters R1a (%) (all data) wR2b (%) (all data) Goodness-of-fit (GOF) on F2 Largest difference in peak and hole (e Å3)
C54H70F2Mo2O10 1108.98 150(2) monoclinic, P21/c 10.1027(2) 15.2966(4) 17.1975(4)
C54H70Cl2Mo2O10 1141.88 152(2) monoclinic, P21/c 10.5454(3) 28.4540(9) 10.0650(3)
94.985(2)
115.025(1)
2647.60(11) 2 1.391 0.38 0.38 0.23 2.378–27.454 0.536 46 777 6037 (0.049) 99.9% (25.242)] 6037/15/307 3.65 (5.25) 8.85 (9.98) 1.079 0.736 and 0.505
2736.57(14) 2 1.386 0.38 0.23 0.19 1.431–27.438 0.610 40 716 6237 (0.051) 100.0% (25.242) 6237/0/307 4.41 (7.12) 10.91 (12.65) 1.101 1.534 and 0.595
C54H70Br2Mo2O10 1230.80 150(2) triclinic, P 1 10.0697(2) 10.5101(2) 14.8323(2) 73.389(1) 80.287(1) 64.104(1) 1351.45(4) 1 1.512 0.27 0.19 0.15 1.435–27.475 1.997 35 192 6194 (0.048) 99.9% (25.242) 6194/0/307 3.76 (6.17) 9.0 (11.9) 1.12 0.90 and 1.47
C54H70I2Mo2O10 1324.78 150(2) triclinic, P 1 10.0917(3) 10.4630(2) 14.7965(4) 76.668(2) 86.366(1) 65.537(2) 1382.87(7) 1 1.591 0.31 0.27 0.19 1.415–27.426 1.623 35 285 6286 (0.041) 100.0% (25.242) 6286/0/307 3.81 (6.35) 9.41 (12.77) 1.116 2.111 and 0.969
P P ||Fo| |Fc||/ |Fo| 100. hP i P wR2 = w(F2o F2c )2/ (w|Fo|2)2 1/2 100. R1 =
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Fig. 5. ORTEP drawings of 1 (F,Cl) and 2 (F–I) drawn at 50% probability. Solvent and hydrogen atoms removed for clarity.
gen shifting to lower energy with a progression down the group. We observed minimal change in the excited state lifetimes as the halogen was varied. This implies that the S1 and T1 lifetimes are dictated primarily by the heavy atom effect of the Mo2 core rather than the ancillary halogens. In the solid state we observed that the packing of the molecules was contingent upon the identity and quantity of the attending halobenzoate. The trans compounds containing Br and I were shown to assemble in a linear, 1-D type arrangement, facilitated by halogen– halogen interactions. This interaction was not seen, however, in the more electronegative ligands containing F and Cl indicating a weaker halogen–halogen interaction and, instead, favoring pp stack ing. Increasing the number of attending halogens however did afford 1-D packing as the Cl containing homoleptic compound was able to bind through all four arms. This interaction, while subtle, could facilitate crystal engineering of Mo2(O2CR)4 compounds in the future.
3. Experimental 3.1. General methods All solvent were dried and distilled from appropriate agents and stores over 4 Å molecular sieves in Kontes top flasks. All reactions and preparations were perform under UHP argon using standard Schlenk and glovebox techniques. Mo(CO)6 was purchased from Alfa Aesar and used as received. The halogenated benzoic acids were purchased from Sigma Aldrich Chemical Co. and used as received. Mo2(TiPB)4 was prepared according to a previously published procedure [3]. NMR spectra were taken a on a 400 MHz Bruker DPX Advance 400 spectrometer. All 1H NMR chemical shifts are in parts per million (PPM) relative to the protio impurity at, 2.50 for DMSO-d6 and 3.58 for THF-d8.
Fig. 6. Cl–Cl laddering of the homoleptic compound 1-Cl.
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Fig. 7. Top down and side on view showing the Br–Br interactions in 2-Br.
Fig. 8. Top down and side on view showing the I–I interactions in 2-I.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were obtained on a Bruker Microflex mass spectrometer. Dithranol was used as a matrix. Samples were prepared by adding a solution of the matrix to the solid sample, which was then spotted for analysis. An internal standard was employed to calibrate the observed peaks. 3.2. Electronic absorption spectra UV–Vis–NIR electronic spectra in THF solutions were measured at room temperature using a Perkin–Elmer Lambda 900 spectrometer using 1 cm 1 cm quartz cuvettes sealed with Kontes tops. 3.3. Steady state emission spectra The steady-state luminescence spectra between 350 and 800 nm were acquired on a SPEX Fluoromax-2 spectrofluorometer. The spectra were measured in THF at room temperature and in 2-methyltetrahydrofuran at 77 K. Samples were excited into their MLCT bands. The steady-state near-IR luminescence spectra were
taken on a home-built instrument utilizing a germanium detector. All measurements were recorded in 2-methyltetrahydrofuran using an excitation wavelength of 405 nm. 3.4. Time-resolved measurements Time-resolved infrared21 spectroscopy experiments were performed with a Ti:sapphire and regenerative amplifier combination (1 kHz, 300 fs fwhm) that has been previously described. Samples of 2-I, 2-Br, 2-Cl, and 2-F were prepared in THF with an absorbance of 1 at kmax. Solutions were sealed in a PerkinElmer semidemountable cell with a 0.1 mm Teflon spacer between 4 mm CaF2 windows. Compounds 2-I, 2-Br, 2-Cl, and 2-F were excited at 350 nm with a laser power of 1 lJ. In the ns TA experiment, samples were prepared in a 1 cm quartz cuvette with Kontes top with absorbance 0.1–0.3 and excitation power at the sample of 100 mW [22]. All samples were excited at a wavelength of 355 nm. Kinetics for the time-resolved data were fit to a sum of expoP nentials, S(t) = i Ai exp(1/si)+ C, where Ai is the amplitude, sI is the lifetime, and C is an offset, in Igor Pro 6.0 or SigmaPlot
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Fig. 9. Top down and side on view of the p p stacking seen in 2-F.
Table 4 A summary of solid state interactions from 1 (F,Cl) and 2 (F – I) including the type of halogen–halogen interaction. Compound
C–X X0 angle
C0 –X0 X angle
Interaction
1-F 1-Cl 2-F 2-Cl 2-Br 2-I
– 176.2° – – 162.8° 146.8°
– 85.1° – – 162.8° 146.8°
N/A type 2 halogen–halogen p–p stacking N/A type 1 halogen–halogen type 1 halogen–halogen
12.0. Standard errors of the exponential fits are given as the error bars of the lifetimes. For the TRIR experiments, the transients were fit to Gaussian functions and the peak position was plotted against the delay times. General Synthesis of 1-X. Mo(CO)6 and two equivalents of the respective carboxylic acid were placed into a Schlenk flask and 4:1 o-dichlorobenzene:THF mixture [10–15 mL total]. The mixture was heated to reflux [140 °C] for 48 h. Upon cooling, the THF was removed under vacuum and the product precipitated from solution. The desired product was isolated as a microcrystalline powder by filtration and washing with hexanes [3 15 mL]. General Synthesis of 2-X. Mo2(TiPB)4 and two equivalents of the desired carboxylic acid were combined in a Schlenk flask and dissolved in toluene [10–15 mL]. The reaction mixed at room temperature for 48 h where a precipitate formed. The desired product was isolated by filtration as a powder and was further purified by washings with hexanes [3 15 mL].
1-F. Mo(CO)6 [250 mg, 0.95 mmol] and 4-fluorobenzoic acid [268 mg, 1.91 mmol] produced Mo2(PhF)4 [345 mg, 97%]. NMR (DMSO-d6): dH (400 MHz) 8.23 (dd, 8H, JHH = 8.4 Hz, JHF = 5.3 Hz), 7.38 (t, 8H, JHH = 8.8 Hz, JHF = 8.8 Hz). MALDI-TOF MS: C28H16F4Mo2O8 Calculated: 751.9, Found: 747.0. 1-Cl. Mo(CO)6 [250 mg, 0.95 mmol] and 4-chlorobenzoic acid [304 mg, 1.95 mmol] produced Mo2(PhCl)4 [370 mg, 96%]. NMR (DMSO-d6): dH (400 MHz) 8.16 (d, 8H, JHH = 8.6 Hz), 7.60 (d, 8H, JHH = 8.6 Hz). MALDI-TOF MS: C28H16Cl4Mo2O8 Calculated: 815.8, Found: 812.9. 1-Br. Mo(CO)6 [250 mg, 0.95 mmol] and 4-bromobenzoic acid [398 mg, 1.98 mmol] produced Mo2(PhBr)4 [410 mg, 87%]. NMR (THF-d8): dH (400 MHz) 8.13 (d, 8H, JHH = 8.5 Hz), 7.63 (d, 8H, JHH = 8.5 Hz). MALDI-TOF MS: C28H16Br4Mo2O8 Calculated: 991.6, Found: 990.9. 1-I. Mo(CO)6 [250 mg, 0.95 mmol] and 4-iodobenzoic acid [470 mg, 1.90 mmol] produced Mo2(PhI)4 [510 mg, 91%]. NMR (THF-d8): dH (400 MHz) 7.96 (d, 8H, JHH = 8.0 Hz), 7.74 (d, 8H, JHH = 8.2 Hz). MALDI-TOF MS: C28H16I4Mo2O8 Calculated: 1183.5, Found: 1179.9. 2-F. Mo2(TiPB)4 [100 mg, 0.085 mmol] and 4-fluorobenzoic acid [24 mg, 0.171 mmol] produced Mo2(TiPB)2(PhF)2 [55 mg, 67%]. NMR (THF-d8): dH (400 MHz) 8.40 (dd, 4H, J = 8.4, 5.6 Hz), 7.31 (t, 4H, J = 5.6 Hz) 7.00 (s, 4H), 3.03 (sep, 4H, JHH = 6.9 Hz), 2.87 (sep, 2H, JHH = 6.9 Hz), 1.23 (d, 12H, JHH = 6.9 Hz), 1.03 (d, 24H, JHH = 6.9 Hz). MALDI-TOF MS: C46H54F2Mo2O8 Calculated: 968.2, Found: 965.2. 2-Cl. Mo2(TiPB)4 [200 mg, 0.17 mmol] and 4-chlorobenzoic acid [52.8 mg, 0.34 mmol] produced Mo2(TiPB)2(PhCl)2 [132 mg, 78%]. NMR (DMSO-d6): dH (400 MHz) 8.34 (d, 4H, JHH = 8.5 Hz), 7.60 (d,
M.H. Chisholm et al. / Inorganica Chimica Acta 424 (2015) 300–307
4H, JHH = 8.5 Hz), 7.00 (s, 4H), 3.02 (sep, 4H, JHH = 6.8 Hz), 2.87 (sep, 2H, JHH = 6.8 Hz), 1.23 (d, 12H, JHH = 6.8 Hz), 1.03 (d, 24H, JHH = 7.0 Hz). MALDI-TOF MS: C46H54Cl2Mo2O8 Calculated: 1000.0 Found: 997.6. 2-Br. Mo2(TiPB)4 [600 mg, 0.51 mmol] and 4-bromobenzoic acid [195 mg, 0.97 mmol] produced Mo2(TiPB)2(PhBr)2 [483 mg, 87%]. NMR (DMSO-d6): dH (400 MHz) 8.26 (d, 4H, JHH = 8.6 Hz), 7.77 (d, 4H, JHH = 8.6 Hz) 7.01 (s, 4H), 3.02 (sep, 4H, JHH = 6.6 Hz), 2.88 (sep, 4H, JHH = 6.6 Hz), 1.24 (d, 12H, JHH = 6.6 Hz), 1.04 (d, 24H, JHH = 6.6 Hz). MALDI-TOF MS: C46H54Br2Mo2O8 Calculated: 1088.0 Found: 1085.7. 2-I. Mo2(TiPB)4 [200 mg, 0.17 mmol] and 4-iodobenzoic acid [84 mg, 0.34 mmol] produced Mo2(TiPB)2(PhI)2 [155 mg, 75%]. NMR (THF-d8): dH (400 MHz) 8.09 (d, 4H, JHH = 8.4 Hz), 7.97 (d, 4H, JHH = 8.4 Hz), 7.00 (s, 4H), 3.01 (sep, 4H, JHH = 7.5 Hz), 2.87 (sep, 6H, JHH = 7.0 Hz), 1.23 (d, 12H, JHH = 7.0 Hz), 1.03 (d, 24H, JHH = 7.0 Hz). MALDI-TOF MS: C46H54I2Mo2O8: Calculated: 1184.0, Found: 1181.5. 3.5. Single crystal X-ray diffraction Single crystals of 1 – (F, Cl) and 2 – (F-I) were isolated and handled under a pool of fluorinated oil. Examination of the diffraction pattern was done on a Nonius Kappa CCD diffractometer with Mo Ka radiation. All work was conducted at 150 K using an Oxford Cryosystems Cryostream Cooler. Data integration was performed with Denzo, and scaling and merging of the data was done with Scalepack [23]. The structures were solved by the direct methods program in SHELXS-13 [24]. Full-matrix least-squares refinements based on F2 were performed in SHELXL-13 [24], as incorporated in the WinGX package [25], For each methyl group, the hydrogen atoms were added at calculated positions using a riding model with U(H) = 1.5Ueq (bonded carbon atom). The rest of the hydrogen atoms were included in the model at calculated positions using a riding model with U(H) = 1.2Ueq (bonded atom). Neutral atom scattering factors were used and include terms for anomalous dispersion [26]. Acknowledgements The authors would like to thank the National Science Foundation for funding this research on grant numbers 0957191 and 1266298. We also acknowledge Professor Claudia Turro for use of instrumentation and The Ohio State University Center for Chemical and Biophysical Dynamics for laser systems.
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