Article pubs.acs.org/IC
Cr(III)-HMC (HMC = 5,5,7,12,12,14-Hexamethyl-1,4,8,11tetraazacyclotetradecane) Alkynyl Complexes: Preparation and Emission Properties Sarah F. Tyler,† Eileen C. Judkins,† You Song,‡ Fan Cao,‡ David R. McMillin,† Phillip E. Fanwick,† and Tong Ren*,† †
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
‡
S Supporting Information *
ABSTRACT: Presented here is the chemistry of CrIII alkynyl complexes based on the rac-HMC and meso-HMC ligands (HMC = 5,5,7,12,12,14hexamethyl-1,4,8,11-tetraazacyclotetradecane). Thus far, two pairs of cis/ trans-[Cr(rac/meso-HMC)(C2R)2]Cl (R = Ph, C2H/C2SiMe3) complexes have been synthesized from reactions between cis/trans-[Cr(rac/mesoHMC)Cl2]Cl and LiC2R. These complexes were characterized using single crystal X-ray diffraction, UV−vis spectroscopy, FT-IR spectroscopy, and fluorimetry. Single crystal X-ray diffraction studies revealed that these complexes adopt a pseudo-octahedral geometry. The electronic spectra of both the cis- and trans-[Cr(rac/meso-HMC)(C4R′)2]Cl (R′ = H or SiMe3) complexes exhibit d−d bands with pronounced vibronic progression associated with the asymmetric stretch of the Cr-bound CC bonds. All of these complexes are phosphorescent and show structured emissions originating from the ligand field excited states.
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include a homoleptic [Cr(C2SiMe3)6]3− species16 and several CrIII(Me3 TACN)(C2 R) 3 type complexes (Me 3 TACN = N,N′,N″-trimethyl-1,4,7-triazacyclononane).17 Berke and coworkers investigated alkynylation chemistry based on the combination of chromium and phosphine, which led to a variety of Cr(dmpe) or Cr(depe) bis-alkynyl complexes (dmpe = 1,2-bis(dimethylphosphino)ethane; depe = 1,2-bis(diethylphosphino)ethane) and butadiyne bridged dimer complexes.18 CrIII(cyclam) alkynyl complexes, trans-[Cr(cyclam)(C2R)2]+ and trans-[Cr(cyclam)(1,3-C2C6H4C2H)2]+, were documented by Berben and Long.19 Wagenknecht and coworkers prepared and characterized several [Cr(cyclam)(C2Ar)2]+ type complexes, where selective synthesis of the cis or trans product has been demonstrated.20−22 Our laboratory has specifically investigated the preparation and structural features of trans-Cr(cyclam)(gem-DEE) complexes (gem-DEE = geminal-diethynylene, isotriacetylene).23 Although structurally similar, HMC (HMC = 5,5,7,12,12,14hexamethyl-1,4,8,11-tetraazacyclotetradecane) is simpler and less costly to prepare than cyclam. Due to the two diastereoisomers of HMC (rac and meso), it is also easier to separate the cis/trans starting materials of CrIII(HMC) than it is for CrIII(cyclam). Cr(HMC) complexes have been explored since the 1970s, beginning with a study of two isomeric forms
INTRODUCTION Chemistry of metal alkynyls is an interesting topic from the perspectives of both synthesis and materials applications.1,2 Many mono- and dinuclear metal alkynyls have been investigated as model molecular wires through solution voltammetry and spectroscopy,3 and notable examples include those based on Fe,4 Re,5 Ru,6 and Ru2.7 Examples of molecular conductance measurement in nanojunctions, though limited, further illustrate the promise of metal alkynyls as both true molecular wires8 and active species in flash memory devices.9 Oligomeric/polymeric metal alkynyls based on heavy metals such as Pt and Hg are excellent photovoltaic and optical power limiting materials.10 Many of these works have been based on the combination of 4d/5d metals and soft ligands. Seeking alternative and potentially sustainable metal alkynyl chemistry, several laboratories including ours have investigated 3d metal alkynyl chemistry with cyclam (1,4,8,11-tetraazacyclotetradecane) as the auxiliary ligand.11 The Cr-based complexes are particularly appealing because of both their magnetic (S = 3/2) and emissive characteristics. Preparative chemistry of chromium alkynyl complexes can be traced back to the pioneering work of Nast and co-workers more than half a century ago,12 where complexes such as K3[Cr(C2H)6]13 and Cr0 tricarbonyl alkynyl species14 were investigated. Following this, the macrocyclic complex [CrIII(phthalocyanine)(C2Ph)2]− was reported by Taube et al.15 More recent studies by Berben and Long on CrIII alkynyls © XXXX American Chemical Society
Received: May 27, 2016
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DOI: 10.1021/acs.inorgchem.6b01285 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry of CrII(HMC).24 Over time, the chemistry of Cr(HMC) evolved to include reports of heterometallic donor (RuII)− acceptor (CrIII(HMC)) dyads bridged by cyanide,25 and the metal to metal and metal to ligand emission studies of said complexes,26 as well as magnetic studies of cyanide and hydroxide/aqua bridged complexes utilizing CuII and FeIII.27 To date, there are no reports of any CrIII(HMC)-based alkynyl complexes. Thus, we have endeavored to explore the area of CrIII(HMC) alkynyl complexes for future applications in magnetism, donor−acceptor electron/energy transfer, and optoelectronics. Reported herein are the synthesis and characterization of CrIII(HMC) alkynyl complexes 1 and 2 (Scheme 1).
any peaks corresponding to a hydroamination product such as that encountered in the synthesis of Cr(cyclam) alkynyl complexes.21 All four complexes appear indefinitely stable under ambient conditions. Room-temperature magnetic susceptibility data of complexes 1 and 2 are consistent with a S = 3/2 CrIII center (see a more detailed discussion below), which precludes the use of NMR spectroscopy for meaningful characterization. Complexes 1 and 2 were authenticated using ESI mass spectrometry, and the purity of isolated materials was established with elemental analysis. Consistent with the exceptional stability of a d3 center, complexes 1 and 2 displayed no significant waves in their voltammograms (see SI, Figure S1), and hence no further electrochemical study was pursued. All complexes were characterized with single crystal X-ray diffraction. The cations 1+ and 2+ were all crystallized as the chloride salts. The molecular structures of 1a+, 1b+, 2a+, and 2b+ are shown in Figures 1−4, respectively, and the selected bond lengths and bond angles are collected in Table 1. The CC bond lengths in all cations fall within the range expected for triple bonds.2
Scheme 1. Synthesis of CrIII(HMC) Alkynyl Complexes
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Figure 1. Perspective view of 1a+ at 30% probability level. H atoms were omitted for clarity.
RESULTS AND DISCUSSION The reaction between cis/trans-[Cr(rac/meso-HMC)Cl2]Cl28 and the appropriate lithium alkynyl produced the bis-alkynyl complexes 1a/b and 2a/b (Scheme 1). The orientation of the alkynyl units around the CrIII center is completely dependent on the starting material used: cis/rac starting material yields a cis/rac product, and trans/meso starting material yields a trans/ meso product. In contrast, similar alkynylation reactions of [M(cyclam)X2] (frequently a mixture of cis and trans isomers; X as halide or triflate) led to mostly trans-[M(cyclam)(C2R)2]+.11 Complexes 1a and 2a were prepared from the reactions of cis-[Cr(rac-HMC)Cl2]Cl with 5 equiv of LiC2Ph and 3 equiv of LiC4SiMe3, respectively, and isolated as orange/ brown solids in yields of 35% and 23%, respectively. Complexes 1b and 2b were prepared from the reactions of trans[Cr(meso−HMC)Cl2]Cl with 5 equiv of LiC2Ph and 3 equiv of LiC4SiMe3, respectively, and isolated as bright yellow solids with yields of 52% and 53%, respectively. Although LiC4SiMe3 is always used to synthesize the butadiynyl complexes, the final product obtained when using the trans starting material is always desilylated. Clearly, synthesis of the cis complexes resulted in lower yields, and products were more difficult to isolate due to their solubility in diethyl ether and their propensity to form oils when using solvents such as hexanes. ESI mass spectra of the crude reaction mixtures did not reveal
Figure 2. Perspective view of 1b+ at 30% probability level. H atoms were omitted for clarity.
All complexes can be considered as having an octahedral coordination sphere. The ease with which the cis and trans compounds are obtained is due almost entirely on the diastereoisomers of the HMC ligand. It is well-known that the nitrogen plane of rac-HMC (also known as tet-b) ligand is most commonly folded, whereas the nitrogen plane of mesoHMC (also known as tet-a) is rarely anything but planar (Scheme 2).28−31 Depending on the reaction conditions, B
DOI: 10.1021/acs.inorgchem.6b01285 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Scheme 2. Stereoisomers of HMCa
a The folding axis for cis-[Cr(rac-HMC)(C2R)2]Cl complexes is shown as the red dotted line.
Figure 3. Perspective view of 2a+ at 30% probability level. H atoms were omitted for clarity.
coordinating ligands, and counterions, it is possible for racHMC complexes to rearrange from folded to planar29,32 (never from rac-HMC to meso-HMC, however),31 which is not the case here. The CrC bond lengths in 1b+ are similar to those observed for trans-[Cr(cyclam)(C2Ph)2]+, but are slightly longer by ca. 0.012 Å; there is a negligible difference between the averaged CC bond lengths.22 In a comparison of 1a+ and cis-[Cr(cyclam)(C2Ph)2]+, the CrC bond lengths in 1a+ are also longer by ∼0.012 Å. Additionally, the averaged CC bond length of 1a+ is increased by ∼0.02 Å. As observed in the [Cr(cyclam)(C2Ph)2]+ cis/trans pair, the CrC bonds in 1a+ are also shorter than those in 1b+, owing to the trans influence.20 Comparison of CrC bond lengths in 2a+ and 2b+ reveals the same trans influence effect as that in 1a+ and 1b+. The CC bond lengths in 2a/b+ are comparable to the CC bond lengths in 1a/b+. The single and triple CC bond lengths of the butadiynyl are within the expected ranges, consistent with the acetylenic resonance structure being dominant over either the cumulenic or carbynic structures.2
Figure 4. Perspective view of 2b+ at 30% probability level. H atoms were omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) for 1a+, 1b+, 2a+, and 2b+
Cr1−N1 Cr1−N2 Cr1−N3 Cr1−N4 Cr1−C1 Cr1−C9 C1−C2 C2−C3 C3−C4 C5−C6 C6−C7 C7−C8 C9−C10 C1−Cr1−C9 C1−Cr1−C1′ Cr1−C1−C2 Cr1−C9−C10 N1−Cr1−N3/N1′ N2−Cr1−N4/N2′ N1−Cr1−N2 N1−Cr1−N4/N2′ N2−Cr1−N3/N1′ N3/N2′ −Cr1−N4/N1′
1a+
1b+
2a+
2b+
2.143(2) 2.135(2) 2.138(2) 2.160(2) 2.047(2) 2.050(2) 1.199(3)
2.086(1) 2.078(1) 2.101(1) 2.074(1) 2.078(2) 2.092(2) 1.213(2)
2.151(3) 2.132(3)
2.104(1) 2.082(1)
2.045(4)
2.081(1)
1.204(5) 1.385(6) 1.209(6)
1.218(2) 1.380(2) 1.199(2) 1.216(2) 1.384(2) 1.195(2)
1.185(3) 88.52(8)
1.209(2) 177.98(6)
169.0(2) 172.9(2) 86.5(1) 85.3(1) 84.4(1) 164.3(1) 95.6(1) 82.7(1)
173.2(1) 168.5(1) 179.1(1) 179.3(1) 95.6(1) 85.1(1) 85.1(1) 94.2(1)
84.8(2) 172.2(4)
180.00 172.5(1)
165.0(2) 99.1(2) 83.2(1) 87.1(1) 87.1(1) 83.2(1)
180.00 180.00 84.6(1) 95.4(1) 95.4(1) 84.6(1)
C
DOI: 10.1021/acs.inorgchem.6b01285 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Room-temperature magnetic susceptibility measurements of solid samples yielded effective magnetic moments of 3.51, 3.51, 3.92, and 3.50 μB for complexes 1a−2b, respectively. With the exception of 2a, the effective magnetic moments are significantly lower than the spin-only value expected for S = 3 /2 (3.87 μB), but are still within range to be consistent with a CrIII center. In order to gain an in-depth understanding of the spin characteristics of these new CrIII alkynyls, both the temperature dependence of the magnetic susceptibility (χM) and field-dependent magnetization measurements of complexes 2a and 2b were carried out. As shown in Figure 5, at room
Figure 5. Temperature dependence of magnetic property in the form of χMT for 2b and the theoretical fit according to the ZFS model (solid red line).
temperature χMT of complex 2b is 1.67 cm3 K mol−1, which is slightly lower than the theoretical value 1.875 cm3 K mol−1 corresponding to a CrIII ion with S = 3/2 and g = 2. χMT remains almost constant over the entire temperature range, decreases slightly below 7 K, and reaches a minimum of 1.41 cm3 K mol−1, which is consistent with the simple paramagnetic nature of CrIII. Additional evidence can be obtained from the variable-field magnetization. With the increasing field, the magnetization of complex 2b increases and maintains a constant M = 2.75 NμB above 5 T, which corresponds to the value for three unpaired electrons. The variable-temperature magnetic susceptibility data were fitted using the PHI program33 with a zero-field splitting (ZFS) model taking into consideration zj′ as the intermolecular interaction to give the best results with g = 1.88, D = −0.52 cm−1, and zj′ = −0.06 cm−1 (see SI, Figure S2). The negligible intermolecular interaction indicates that the slight decrease of χMT results from the zero-field splitting of the CrIII ion. Complex 2a shows similar magnetic properties with a room-temperature χMT value of 1.75 cm3 K mol−1 and a saturation magnetization of 2.74 NμB under the same measuring field and temperature. The best fitting results are g = 1.90, D = −0.56 cm−1, and zj′ = −0.04 cm−1 (see SI, Figures S3 and S4). The UV−vis absorption spectra of 1 and 2 are shown in Figure 6. All complexes display structured d−d bands between 300 and 450 nm. The molar extinction coefficients of the structured bands are between 500 and 3000 M−1 cm−1. In both pairs, the cis complexes (1a, 2a) exhibit higher extinction coefficients along with an additional, albeit weak, d−d band (∼545 nm). Although not shown, all complexes exhibit intense absorptions below ∼350 nm (1a/1b) and ∼300 nm (2a/2b), which are associated with charge transfer (CT) and intraligand transitions.20−22 The trans complexes are slightly blue-shifted
Figure 6. UV−vis absorption spectra of 1a/1b (A; blue and orange, respectively) and 2a/2b (B, blue and orange, respectively) in CH2Cl2.
compared to their cis counterparts. These results are similar to those found for cis/trans-Cr(cyclam)(C2R)2 complexes.20 To understand the exact origins of the transitions observed for 1 and 2, it is worth mentioning that the absorption spectra of a series of cis- and trans-[Cr(HMC)X2]1+ (X as either halide or pseudohalide) type complexes were reported by House et al.,28 where three ligand field (d−d) bands were assigned as 4 A2g to 4T1g(F), 4T2g(F), and 4T1g(P) under an approximate Oh symmetry. Generally, these transitions appear as broad peaks of modest intensity (ε < 100) with the absorption maxima for the cis complexes slightly blue-shifted from those of the corresponding trans species. For instance, cis-[Cr(HMC)Br2] Br absorbs at 595, 438, and 250 nm, while trans-[Cr(HMC)Br2]Br absorbs at 600, 410, and 374 nm. Clearly, the replacement of halide ligands with alkynyl ligands results in a significantly stronger ligand field. Consequently, the 4T1g(P) term is either beyond the typical UV−vis window or buried under the CT bands. Additionally, the d−d bands in 1 and 2 are about 10−30 times more intense than those of [Cr(HMC)X2]+, indicating a partial charge transfer character due to the strong dπ−π(CC) mixing. The most striking feature of the UV−vis spectra of 1 and 2 is the highly structured nature of the d−d bands, which is clearly D
DOI: 10.1021/acs.inorgchem.6b01285 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry the consequence of vibronic coupling. Vibronic progressions have been calculated and are given in the Supporting Information (Figure S5). In the cases of 1a and 1b, the vibronic progressions are between 800 and 900 cm−1 (av 874 and 868 cm−1, respectively). Because of the possible occurrence of aromatic CH bending, NH bending, and CH2 rocking in this region, it is difficult to speculate the vibrational mode responsible for the observed vibronic progressions. On the other hand, complexes 2a and 2b have averaged vibronic progressions of ca. 2023 and 1971 cm−1, respectively, which are close to the CC stretching frequencies found for 2a (2162, 2126, and 2008 cm−1) and 2b (2134 and 1981 cm−1) (Figure 7). They are thought to be associated with the asymmetric
Figure 7. Solid state FT-IR spectra of 2a (red) and 2b (blue).
stretch of the Cr-bound CC units. It should be noted that the discussion of vibronic progressions herein is qualitative, while the quantification of such an effect requires a far more sophisticated spectroscopic study even for seemingly simple organic molecules.34 Full FT-IR spectra for 1a−2b can be found in the Supporting Information (Figures S6 and S7). Similar to the previously studied [Cr(cyclam)(C2R)2]+ species,20−23 complexes 1 and 2 are phosphorescent. The emission spectra of complexes 1 and 2 are shown in Figure 8 (frozen glass) and Figure S8 (overlay of room-temperature, solid state, and frozen glass emissions), while relevant parameters are collected in Table 2. As discussed above, assuming an approximate octahedral symmetry, there are two possible spin-allowed excitations from the ground state 4A2g to the excited states 4T1g and 4T2g. Phosphorescence then occurs after intersystem crossing from these excited states to the lower lying doublet states, 2Eg and/or 2T1g. Complexes 1 and 2 exhibit strong emissions from 2T1g (Figure 8) with pronounced fine structuring. In general, the trans complexes exhibit more highly structured emissions than their cis counterparts, and they are well-resolved in the frozen glass spectra. These structured emissions are believed to be of vibronic origin, as noted in other Cr(HMC) and Cr(cyclam) complexes.35 The emission of cis-[Cr(rac-HMC)Cl2]Cl at 77 K is also structured, similar to 1a and 1b in glass, albeit at lower wavelengths.36 Closer inspection of the spectra shown in Figure 8 reveals that the λmax of the trans complexes are generally blue-shifted from those of the cis complexes. The peak positions of complexes 2a and 2b are red-shifted from those of 1a and 1b as well; however, differences in the ligands preclude a simple
Figure 8. Emission spectra of 1a/1b in a 4:1 ethanol/methanol glass (A; blue line and orange line, respectively) and 2a/2b (B; blue line and orange line, respectively) taken at 77 K.
comparison. From the studies of [Cr(cyclam)(CN)2]+ and [Cr(HMC)(CN)2]+, it was expected that the emissions of 1 and 2 would stem from the 2Eg excited state, which is usually seen between 650 and 720 nm.35 However, the emissions of 1 and 2 are red-shifted from the expected range for 2Eg. This corresponds more closely to a transition solely from the 2T1g state, as is consistent with related Cr(cyclam) systems.20−23 An example of this is the complex trans-[Cr(HMC)F2]ClO4, which has an intense 2T1g → 4A2g emission at 778 nm, resembling the solid state emissions seen for 2b and potentially 1b.37 Overall, the lifetimes of the trans-complexes (1b and 2b) are longer than those of the cis-complexes (1a and 2a) (Table 2). For all of the complexes, the lifetimes in glass at 77 K are significantly longer than those in the solid state at 77 K. In the cases of 1a and 2a, the lifetimes increase from ca. 53 and 28 μs in the solid state, respectively, to 212 and 129 μs in frozen glass, respectively. For 1b and 2b, the lifetimes increase from 198 and 261 μs in the solid state, respectively, to 469 and 455 μs in glass, respectively. It was shown previously that the distortion in the CrN2C2 plane of the cis complexes (deviations of L−Cr−L from 90°) resulted in larger nonradiative decay rates (knr), and consequently shorter emission lifetimes,38 which may explain the shorter lifetimes observed for 1a and 2a. E
DOI: 10.1021/acs.inorgchem.6b01285 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Table 2. Photophysical Data for Complexes 1 and 2 room tempa 1a 1b 2a 2b a
solid stateb
frozen glassc
λex (nm)
λmax (nm)
λex (nm)
λmax (nm)
τ (μs)
λex (nm)
λmax (nm)
τ (μs)
424 425 402 402
764 746 771 746
440 430 440 445
766 769 778 772
53.2 198 28.2 261
425 425 443 405
763 744 777 771
212 469 129 455
In degassed acetonitrile. bTaken at 77 K. cDissolved in a 4:1 ethanol/methanol glass, taken at 77 K.
Table 3. Crystal Data for Complexes 1a, 1b, 2a, and 2b
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chemical formula fw space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z T, K λ, Å ρcalcd, g cm−3 R Rw(F2)
1a
1b
2a
2b
C32H46CrN4, Cl 574.20 Pbca (No. 61) 19.0947(3) 15.2858(2) 21.6894(5)
C32H46CrN4, Cl, 2(CH4O) 638.28 P21/c (No. 14) 9.2959(7) 21.2086(11) 17.4776(10)
C30H54CrN4Si2, Cl 614.41 Pbcn (No. 60) 12.2089(5) 12.8204(5) 22.5411(14)
C24H38CrN4, Cl, 3(CH4O) 566.17 P1̅ (No. 2) 10.0216(5) 12.0315(6) 13.4308(4) 86.353(3) 72.292(3) 80.406(2) 1521.0(1) 2 150 0.7103 1.236 0.034 0.090
92.872(4) 6330.7(2) 8 295 0.71073 1.205 0.040 0.102
3441.4(4) 4 150 0.70173 1.232 0.040 0.110
3528.2(3) 4 150 1.54184 1.157 0.061 0.145
General Synthetic Procedure. To a Schlenk flask containing cisor trans-[Cr(rac/meso-HMC)Cl2]Cl in THF was added the appropriate lithiated alkynyl in excess, yielding a dark brown/orange solution that becomes yellow (trans) or orange (cis) when quenched with MeOH. The reaction mixture was filtered over Celite, and the product was purified over a silica gel pad with a CH2Cl2−MeOH (v/v, 50:1) eluent. cis-[Cr(rac-HMC)(C2Ph)2]Cl (1a). The reaction between 0.300 g of cis-[Cr(rac-HMC)Cl2]Cl (0.68 mmol) and 5 equiv of LiC2Ph yielded 0.138 g of 1a (0.24 mmol; 35% based on Cr) after recrystallization from MeOH/diethyl ether. UV−vis, λmax/nm (ε/M−1 cm−1): 369 (960), 382 (1130), 395 (1250), 409 (1340), 425 (sh), 442 (750). FTIR ν(CC)/cm−1: 2081 (w). Elem. Anal. Found (Calcd) for cis[Cr(rac-HMC)(C2Ph)2]Cl: C, 66.90 (66.94); H, 8.10 (8.08); N, 9.65 (9.76). trans-[Cr(meso-HMC)(C2Ph)2]Cl (1b). The reaction between 0.102 g of trans-[Cr(meso-HMC)Cl2]Cl (0.23 mmol) and 5 equiv of LiC2Ph yielded 0.0711 g of 1b (0.12 mmol; 52% based on Cr) after recrystallization from THF (with minimal CH2Cl2) and diethyl ether. UV−vis, λmax/nm (ε/M−1 cm−1): 352 (sh), 361 (1000), 373 (1040), 387 (1010), 400 (1060), 414 (sh), 431 (640). FT-IR ν(CC)/cm−1: 2055 (w). Elem. Anal. Found (Calcd) for trans-[Cr(meso-HMC)(C2Ph)2]Cl·3H2O: C, 61.08 (61.18); H, 8.43 (8.34); N, 8.70 (8.92). cis-[Cr(rac-HMC)(C4SiMe3)2]Cl (2a). The reaction between 0.486 g of cis-[Cr(rac-HMC)Cl2]Cl (1.1 mmol) and 3 equiv of LiC4SiMe3 yielded 0.157 g of 2a (0.26 mmol; 23% based on Cr) after recrystallization from CH2Cl2 (with minimal MeOH) and diethyl ether/hexanes. UV−vis, λmax/nm (ε/M−1 cm−1): 325 (1030), 348 (1420), 375 (2140), 404 (2810), 440 (1620). FT-IR ν(CC)/cm−1: 2162 (m), 2126 (m), 2008 (m). Elem. Anal. Found (Calcd) for cis[Cr(rac-HMC)(C4SiMe3)2]Cl·0.5H2O: C, 58.10 (57.80); H, 8.85 (8.89); N, 8.57 (8.98). trans-[Cr(meso-HMC)(C4H)2]Cl (2b). The reaction between 0.243 g of trans-[Cr(meso-HMC)Cl2]Cl (0.55 mmol) and 3 equiv of LiC4SiMe3 yielded 0.134 g of 2b (0.29 mmol; 53% based on Cr) after recrystallization from THF (with minimal MeOH) and diethyl ether. It should be noted that although the reaction uses LiC4SiMe3,
CONCLUSION The chemistry of CrIII bis-alkynyl complexes has now been extended to include Cr(HMC) through the successful synthesis of the cis/trans pairs 1 and 2. Complexes 1 and 2 exhibit interesting spectroscopic properties, including intense structured features in both their absorption and emissions spectra. All of the complexes display long-lived phosphorescence in a frozen glass, with 1b and 2b also having long-lived lifetimes in the solid state at 77 K. Having achieved facile synthesis of cis/ trans-Cr(rac/meso-HMC) bis-alkynyl complexes 1 and 2, we will focus on the preparation of Cr(HMC) complexes with elaborately functionalized alkynyls for the assembly of supramolecules with interesting magneto- and optoelectronic properties.
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EXPERIMENTAL SECTION
General. Phenylacetylene and 1,4-bis(trimethylsilyl)butadiyne were purchased from GFS Chemicals. HMC,30 trans-[Cr(meso-HMC)Cl2]Cl, and cis-[Cr(rac-HMC)Cl2]Cl28 were prepared according to the literature procedures. It should be noted that there are two procedures for the synthesis of both trans-[Cr(meso-HMC)Cl2]Cl and cis-[Cr(racHMC)Cl2]Cl mentioned in the work of House et al.;28 for this work, a mixture of ligand diastereoisomers was used in a one pot synthesis to prepare trans-[Cr(meso-HMC)Cl2]Cl and cis-[Cr(rac-HMC)Cl2]Cl. Tetrahydrofuran was freshly distilled over Na/benzophenone. All reactions were performed under a dry N2 atmosphere using standard Schlenk procedures unless otherwise noted. UV−vis spectra were obtained with a JASCO V-670 spectrophotometer in CH2Cl2 solutions. FT-IR spectra were measured as neat samples with a JASCO FT/IR-6300 spectrometer equipped with an ATR accessory. ESI mass spectra were recorded on a Waters 600 LC/MS. Magnetic susceptibility measurements were conducted using a Johnson Matthey Mark-I magnetic susceptibility balance. Emission data were recorded on a Varian Cary Eclipse fluorescence spectrophotometer. F
DOI: 10.1021/acs.inorgchem.6b01285 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry the isolated product is always desilylated. UV−vis, λmax/nm (ε/M−1 cm−1): 312 (690), 332 (970), 354 (1250), 381 (1220), 411 (650). FTIR ν(CC)/cm−1: 2134 (w), 1981 (w). Elem. Anal. Found (Calcd) for trans-[Cr(meso-HMC)(C4H)2]Cl·0.5CH3OH·2H2O: C, 56.25 (56.36); H, 8.31 (8.49); N, 10.55 (10.73). Magnetic Measurements. The temperature-dependent magnetic properties were measured using crystalline samples on a Quantum Design MPMP VSM SQUID magnetometer. The corrections of the magnetic susceptibilities were carried out considering both the sample holder as the background and the diamagnetism of the constituent atoms estimated from Pascal’s constant.39 X-ray Structural Analysis of 1 and 2. Single crystals of complexes 1a and 2a were grown via slow diffusion of hexanes into concentrated CH2Cl2 and THF solutions, respectively, and those of 1b and 2b were grown via slow diffusion of diethyl ether into a concentrated THF/MeOH solution. X-ray diffraction data for 1a, 1b, and 2b were collected on a Nonius KappaCCD diffractometer using Mo Kα (λ = 0.71073 Å) at 295 K (1a) and 150 K (1b and 2b), and data for 2a on a Rigaku Rapid II image plate diffractometer using Cu Kα (λ = 1.54184 Å) at 150 K (Table 3). The structures were solved using the structure solution program PATTY in DIRDIF9940 and refined using SHELXTL.41
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01285. UV−vis and FT-IR spectra, cyclic voltamogramms, magnetic data for complexes 1 and 2, and emission plots (PDF) X-ray crystallographic details for the structural determination of 1a, 1b, 2a, and 2b (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is supported by both the National Science Foundation CHE 1362214 (Purdue) and the National Natural Science Foundation of China 21571097 (Nanjing).
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