Crystal Engineering Gone Awry. What a Difference a Few Methyl

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Crystal Engineering Gone Awry. What a Difference a Few Methyl Groups Make in Fullerene/Porphyrin Cocrystallization Kamran B. Ghiassi, Xian B. Powers, Joseph Wescott, Alan L. Balch,* and Marilyn M. Olmstead* Department of Chemistry, University of California, Davis, 95616, United States S Supporting Information *

ABSTRACT: Two related nickel(II) porphyrins, etioporphyrin-I (Etio-I) and octaethylporphyrin (OEP), were cocrystallized with C70 to produce the new cocrystal structures C70·Ni(Etio-I)·2C6H6 and C70·Ni(OEP)·2C6H6. Etio-I is a variant of OEP, where four alternating ethyl groups from OEP are replaced with methyl substituents. This isomer of etioporphyrin has the potential to act as an agent in chiral sorting of asymmetric fullerenes. However, the replacement of four ethyl groups has nontrivial structural consequences. Further host−guest investigation of M(Etio-I) (M = Co, Ni, Cu, Zn) with C60 or C70 was conducted, producing new X-ray structures of Co(Etio-I) and Zn(Etio-I), and a redetermination of Ni(Etio-I). Despite numerous and varied attempts, C60 cocrystallized with M(Etio-I) could not be obtained.

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examined to date (e.g., Sc3N@D3(6140)-C68,14 D2-C76(S8)6,15 C1(30)-C90,16 and C1(32)-C9016) crystallographic characterization has involved mixtures of the two enantiomers with the two cages randomly occupying similar sites within the respective crystal. As a result, the analysis of the diffraction data is difficult, and the quality of the structural parameters is significantly below that of fully ordered structures. To alleviate these problems, we intended to devise a new cocrystallization procedure that should allow us to sort fullerene enantiomers (as guests) into distinct crystallographic sites without prior separation. To do this, a racemate of a chiral host molecule will be utilized for cocrystallization. The concept is shown in Scheme 1 for the

INTRODUCTION Since their discovery in 1985, fullerenes have received much attention in science.1 The first fullerene, C60, is often termed a molecular soccer ball due to its highly symmetrical and spherical nature. In the realm of host−guest chemistry, nothing is more satisfying than playing molecular catch with a buckyball. To determine whether the chemist has successfully “caught” the fullerene, X-ray crystallography is employed. However, even when the buckyball (guest) is caught, the molecular glove (host) may not sufficiently hold it in place. This often results in disorder. Since this particular host−guest chemistry is governed by intermolecular interactions, the molecular gloves must take advantage of van der Waals forces. Typically, π---π, C−H---π, and C−X---π interactions are observed in their crystal structures. Fullerenes have been successfully cocrystallized with a variety of extended π-system molecular gloves featuring curves (e.g., corannulene), 2 bowls (e.g., hexakis[(E)-3,3-dimethyl-1butenyl]benzene,3 calixarenes4), and even planes (e.g., porphyrins5−9 and bis(ethylenedithio)tetrathiafulvalene10,11). Although counterintuitive to the game of molecular catch, fullerenes are surprisingly well-behaved crystallographically when caught by flat porphyrins. In order to determine the structures of new fullerenes and endohedral fullerenes, we have found that cocrystallization with Ni(OEP) (OEP is the dianion of octaethylporphyrin) produces sufficiently ordered crystals to allow determination of the cage structure and positioning of metal atoms or clusters inside the cage. Intrinsically chiral fullerenes, where the chirality resides within the core structure of the molecule, offer new materials with interesting structures and chiro-optical properties for materials applications.12,13 Structural characterization of these fullerenes is challenging. Moreover, when presented with a new fullerene to structurally characterize, we do not know whether a chiral cage is present. In many cases © XXXX American Chemical Society

Scheme 1. Sorting Through Cocrystallization

Received: October 10, 2015 Revised: December 4, 2015

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DOI: 10.1021/acs.cgd.5b01449 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Scheme 2. Chemical Structures of Ni(OEP) and Ni(Etio) Isomers

case where (S)-host combines with (R)-fullerene, etc. Alternatively the preferred pairing might combine (S)-host with (S)fullerene. In somewhat related work, several porphyrin-based hosts for fullerenes have been prepared and utilized for fullerene complexation, including enantioselective complexation of chiral C76.17,18 If four ethyl groups of OEP are replaced with methyl substituents, the molecule becomes etioporphyrin (Etio). Depending on how the methyl/ethyl groups are arranged around the macrocycle, different isomers are generated as shown in Scheme 2. We became interested in etioporphyrin-I due to its potential to serve as a chiral host for chiral fullerenes.12,13 Although the molecule is intrinsically achiral, it may become chiral during cocrystallization. Our hopes were to utilize metalated etioporphyrin-I molecules to crystallographically sort chiral fullerenes. Here, we report efforts to obtain cocrystals of the readily available C60 and C70 with M(Etio-I) (M = Co, Ni, Cu, Zn) along with the structures of the cocrystals C70·Ni(OEP)·2C6H6 and C70·Ni(Etio-I)·2C6H6 (Etio-I) = etioporphyrin-I. This study allows us to compare and contrast the outcome of the replacement of four of the ethyl groups by methyl groups. In addition, the structures of pristine Ni(Etio-I), Co(Etio-I), and Zn(Etio-I) are reported. Although the crystal structure of Ni(Etio-I) was published over 50 years ago,19 our structure assignment gives a lower symmetry, yet ordered, portrayal of the molecule.

solvate crystals. The same observation was made in the case of C70, with only one exception. When both components were dissolved in benzene and allowed to slowly diffuse, a few crystals of C70·Ni(Etio-I)·2C6H6 formed after several months. Under the same conditions, many crystals of the Ni(OEP) counterpart, C70· Ni(OEP)·2C6H6, formed in less than a day. In regard to Co(EtioI) as a potential host, it was noticed that the solutions were slightly air sensitive and gradually formed mirrors in the crystallization vessels over a period of months. We also attempted cocrystallization of fullerenes with Cu(Etio-I) and Zn(Etio-I) porphyrins with no success. Thus, while Ni(OEP) reliably and readily forms cocrystals with almost any fullerene or endohedral fullerene, the prospects for using M(Etio-I) for cocrystallization with fullerenes and using it for chiral sorting are dim. Crystals suitable for X-ray diffraction of Ni(Etio-I), Co(EtioI), and Zn(Etio-I) were obtained by similar slow diffusion experiments during cocrystallization attempts. Rather than producing cocrystals, both crystals of the metalated porphyrins grew concomitantly with fullerene solvates or a noncrystalline fullerene precipitate in a variety of different solvents. In particular, C60 dissolved in benzene layered over Co(Etio-I) dissolved in chloroform produced red needles of Co(Etio-I) among black blocks of C60·4C6H6.20 The crystals were examined via X-ray diffraction to confirm unit cells. The same concomitant crystal growth occurs while using M(Etio-I) (M = Co, Ni, Cu, Zn) and C70 in toluene where crystals of M(Etio-I) and C70·C7H8 form.21 C70 ·Ni(Etio-I)·2C6H 6 . The structure is found in the monoclinic setting, space group P21/c with Z = 4. Crystal data are given in Table 1. The asymmetric unit contains a Ni(Etio-I) molecule, two benzene molecules, and a C70 cage on general positions. The C70 molecule is disordered over two orientations with occupancies that we have assumed to be 0.5:0.5, although the refined occupancies may be as high as 0.60:0.40, depending on assigned restraints. The assignment of a statistical disorder is reasonable based on geometric considerations. The benzene

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RESULTS We attempted cocrystallization of M(Etio-I) (M = Co, Ni, Cu, Zn) with C60 and C70, as they are the two most abundant fullerenes. The experimental setup executed was that of slow diffusion, typical of fullerene crystal growth. Many different solvent combinations were attempted utilizing toluene, benzene, carbon disulfide, dichloromethane, chloroform, and pyridine. In our hands, we were unable to form a cocrystal of C60 with any metalated etioporphyrin-I. Rather, it was observed that the metalated porphyrin would recrystallize concomitantly with C60 B



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evident in this figure. This deformation corresponds to the most nonplanar of the five porphyrin structures reported here. Linear displacement plots are shown in Figure 2. Figure 3 depicts the packing arrangement in the ac plane. This arrangement is repeated by simple translation in the crystallographic a direction. An assumption is made that the disordered C70 cages alternate. The closest distance between the nickel and the fullerene cage is 3.654(13) Å. The closest Ni1---Ni1 distance is 9.3772(15). No remarkable contacts occur between the porphyrin and the cage or between cages. The shortest contacts are represented by lines in Figure 3. Among those, the shortest N---cage distances are 3.229(9) Å and 3.339(8) Å, and the shortest cage---cage distances are 3.114(7) and 3.297(15). Somewhat surprisingly, due to the lateral shift of the porphyrin, contacts between methyl hydrogen atoms and the cage and those between ethyl hydrogens and the cage are similar in length, with the seven shortest values in the range of 2.69−2.87 Å. The Ni(Etio-I) molecule contains a disordered site located at one of the ethyl substituents. The major component of this site is an ethyl group, while the minor component is a bromine group (vide infra). This site possesses an ethyl:bromine refined occupancy ratio of 0.9480(14):0.0520(14). An additional m/z signal was observed in the mass spectrum that matches the formula C30H31N4Br1Ni1, corresponding to the replacement of one ethyl group by a bromine atom as shown in Figure 4. No further mass spectral signals corresponding to additional bromination were detected. It was determined that the source of this impurity lies with the starting material. Several synthetic routes to etioporphyrin-I incorporate the use of molecular bromine.22,23 Although we obtained etioporphyrin-I commercially, it was confirmed that brominated reagents, specifically Br2, were used during its synthesis, as is consistent with our characterization. Despite numerous attempts at purification, this impurity persisted. The four structures containing M(Etio-I) were modeled with this impurity. It should be noted, however, that although the mass spectral data confirms a monobromine impurity, there is crystallographic disorder corresponding to the

Table 1. Crystal Data for C70 Cocrystals chemical formula formula weight radiation source, λ (Å) crystal system space group T (K) a (Å) b (Å) c (Å) β (deg) V (Å3) Z dcalc (g cm−3) μ (mm−1) F(000) crystal size reflections collected data/parameters/restraints R(int) R1 [I > 2σ(I)]a wR2 (all data)a largest difference peak and hole (e Å−3) a

C70·Ni(Etio-I)·2C6H6

C70·Ni(OEP)·2C6H6

C113.89H47.74Br0.05N4Ni 1534.94 sealed tube, 0.71073 monoclinic P21/c 90(2) 13.557(2) 26.135(4) 18.646(3) 90.0181(3) 6605.3(19) 4 1.543 0.394 3156 0.24 × 0.27 × 0.32 115816 22093/1313/840 0.0292 0.0438 [18078] 0.1123 1.281, −0.569

C118H56N4Ni 1588.37 sealed tube, 0.71073 monoclinic P21/c 90(2) 18.8840(9) 14.6258(9) 25.1184(12) 92.416(3) 6931.4(6) 4 1.522 0.349 3280 0.21 × 0.25 × 0.30 116199 23114/1116/0 0.0245 0.0591 [20580] 0.1779 1.661, −0.995

Note: R1 =

⎧ ∑ [w(F 2 − F 2)2 ] ⎫1/2 ∑ ||Fo| − |Fc|| o c ⎬ ; wR 2 = ⎨ 2 2 ∑ |Fo| ⎩ ∑ [w(Fo ) ] ⎭

molecules are ordered. The structure exists as a pseudomerohedral twin caused by the nearness of the β angle to 90°. Figure 1 shows the structure of C70·Ni(Etio-I)·2C6H6 with omission of the second fullerene orientation and the benzene molecules. A ruffled, nonplanar deformation of the porphyrin is

Figure 1. Two orthogonal views showing the molecular components of C70·Ni(Etio-I)·2C6H6 drawn with 50% thermal contours. Disorder, solvate molecules, and hydrogen atoms are omitted for clarity. C



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Figure 2. Linear displacement plots showing planar deviations in the five porphyrin crystal structures.

Figure 3. A view of the packing of C70·Ni(Etio-I)·2C6H6 as it occurs in the ac plane. Rather than superimposing the disordered set of C70 orientations, they are shown as alternating, which yields the most reasonable intermolecular cage---cage contacts. Atoms in red are C1−C70 and in blue are C71− C140. This pattern continues in the cages shown in black.

impurity being delocalized across the remaining ethyl positions. These sites were not included in the structure refinements, since the modeled impurity’s occupancy was already quite low. C70·Ni(OEP)·2C6H6. This structure is also found in the monoclinic setting, space group P21/c with Z = 4. The asymmetric unit, however, is fully ordered containing one C70 cage, one Ni(OEP) molecule, and two benzene molecules, shown in Figure 5. The closest contact between the nickel and the fullerene cage is 2.7851(13) Å. The seven shortest distances between hydrogens of the ethyl groups of the Ni(OEP) and fullerene carbons range from 2.73 to 3.04 Å. Figure 6 shows the packing and some of the intermolecular contacts that exist in this structure. A back-to-back arrangement of the metal porphyrins is a common feature of this sort of cocrystal, and produces a Ni---Ni distance of 3.4608(3) Å in this structure. The shortest N---cage

distances are 3.0128(15) and 3.1368(14) Å. Other contacts are of the π---π type and range from 3.4551(17) Å for cage carbon atom---cage carbon atom, 3.684(2) for benzene carbon atom--cage carbon atom, and 4.021(2) for benzene plane---benzene plane. Co(Etio-I). The structure is found in the triclinic setting, space group P1̅ with Z = 1. The asymmetric unit consists of half of the porphyrin. The porphyrin is nearly planar, but does exhibit a slight wave deformation. Thus, both β-carbons of two opposite pyrrole rings, related by inversion, are displaced above the mean porphyrin plane in one case, below in the other. For the other set of opposing pyrrole rings, one β-carbon is above the mean porphyrin plane while the other is below. A notable difference, however, is that unlike the Ni(Etio-I) structure, the ethyl groups do not alternate up and down. Rather, two are up and two are D



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Figure 4. Mass spectra showing the parent compound Ni(Etio-I) (left) with the persistent bromine impurity (right). Spectra were collected in positive ion mode of detection.

Figure 5. Molecular components of C70·Ni(OEP)·2C6H6 drawn with 50% thermal contours. Solvent molecules and hydrogen atoms are omitted for clarity.

Figure 6. Packing arrangement in C70·Ni(OEP)·2C6H6 showing the unit cell projection.

down. The packing, shown in Figure 7, features a slipped stack of the molecules, with a repeat equal to the length of the crystallographic a axis, 5.4397(2) Å. Since the molecule has a crystallographic center of inversion, the ca. 1% Br disorder occurs in two of the ethyl group sites in the full molecule. Ni(Etio-I). During the course of our investigation with fullerene cocrystallization, a crystal structure of pristine Ni(Etio-I) was obtained. The original structure reported in 1963 was determined in the tetragonal setting, with space group I41/ amd (No. 141).19 This space group is incompatible with the symmetry of Ni(Etio-I) and requires a disorder model that mixes methyl and ethyl positions. From our structure, the space group I41/a (No. 88) shows no disorder with regard to the methyl and ethyl positions. The asymmetric unit consists of one-fourth of the

porphyrin, and the Ni resides on a site with 4̅ symmetry. The porphyrin in its entirety adopts a slightly saddled geometry with each of the four ethyl groups alternating up and down, as shown in Figure 8. As a result of the saddling deformation, molecules of the porphyrin pack in an alternating pattern rather than as a stack of almost planar molecules as is seen in both the Co and Zn analogs. The shortest Ni---Ni distance is 7.8632(7) Å. A portion of the packing is shown in Figure 8. Zn(Etio-I). In this structure the Zn resides on a crystallographic center of inversion. The molecule crystallizes in the monoclinic system, space group P21/n, Z = 2. The porphyrin resembles Co(Etio-I) in its up/down pattern and slight wave deformation of the porphyrin plane Figure 7. The packing is similar as well, although the slipped stacks are tipped in alternate E



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Figure 9. A portion of the slipped stack of molecules in the packing of Zn(Etio-I).

Figure 7. Repeat along the a axial direction in the structure of pristine Co(Etio-I).

recent exception occurs in the crystal structure of LaSc2N@ Cs(hept)-C80·2Ni(OEP)·2C7H8 in which one of the two porphyrins is saddled while the other is planar.24 Interestingly, the saddled porphyrin only has six of its ethyl groups embracing the fullerene. The remaining two ethyl groups of this saddled porphyrin face the opposite direction and form a back-to-back interaction with a neighboring planar porphyrin. In the Ni(EtioI) cocrystal presented in this work, the porphyrin has C70 cages on both sides, as illustrated in Figure 1. In the pristine structure of Ni(Etio-I), the porphyrin shows a slight saddle distortion. Pristine Ni(OEP) has three reported crystal structures: one ruffled (space group I41/a)25 and two planar polymorphs, triclinic A26 and triclinic B.27 In the case of the C70-Ni(Etio-I) cocrystal presented here, the ruffled porphyrin has an average mean out-of-plane displacement of 0.30542(11) Å of the porphyrin plane. However, in our Ni(OEP) cocrystal, the porphyrin is essentially planar, with a very minor curvature (dome) that partially mimics the fullerene curvature. Figure 10 shows the geometric comparison between Ni(OEP) found in the C70 cocrystal and Ni(Etio-I), both in pristine and cocrystallized with C70. Typically, planar metal porphyrins exhibit some form of back-to-back stacking. This feature is entirely absent in the pristine Ni(Etio-I) structure as well as the cocrystal. Side-on views of the metalated Etio-I structures presented here are available in Supporting Information. We originally presumed that the ruffling of the Etio-I porphyrin in the C70 cocrystal was due to the disparity in

rows due to the symmetry of the monoclinic system. The Zn--Zn distance is the a-axis length of 4.8780(3) Å. One such stack is depicted in Figure 9. Crystal data for the three pristine porphyrin compounds are given in Table 2. Atom numbering schemes, together with thermal ellipsoid plots, are found in the Supporting Information. Some selected geometric features of the five porphyrin moieties are collected in Table 3. It is known that deformations of the porphyrin plane impact the size of the porphyrin core. For example, using the trans-N--N distance as a measure of the core size, the small core size of pristine Ni(Etio-I) shows its sensitivity to nonplanar deformation. Even though Ni and Co have approximately the same covalent radius, the more planar Co(Etio-I) has a larger core. The smallest core is found in the structure of C70·Ni(Etio-I)·2C6H6, the most deformed of the five porphyrin structures. Additionally, all the M−N distances can be seen to correlate with the degree of nonplanar deformation.

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DISCUSSION A remarkable feature of C70·Ni(Etio-I)·2C6H6 is the ruffled geometry of the porphyrin. The analogous structure with Ni(OEP) reported by our group in 1999 shows the same 1:1 ratio of Ni(OEP):C70 with a planar porphyrin geometry.5 This is true in most fullerene cocrystal structures with Ni(OEP). A

Figure 8. A view of three adjacent molecules of Ni(Etio-I). F



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Table 2. Crystal Data for M(Etio-I) Structures chemical formula formula weight radiation source, λ (Å) crystal system space group T (K) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z dcalc (g cm−3) μ (mm−1) F(000) crystal size reflections collected data/parameters/restraints R(int) R1 [I > 2σ(I)]a wR2 (all data)a largest diff. peak and hole (e Å−3) a

Co(Etio-I)

Ni(Etio-I)

Zn(Etio-I)

C31.98H35.94Br0.01N4Co 536.07 synchrotron, 0.7749 triclinic P1̅ 100(2) 5.4397(2) 10.8096(5) 11.4000(5) 106.036(2) 93.498(2) 96.022(2) 637.84(5) 1 1.396 0.904 283 0.01 × 0.06 × 0.18 13552 5444/178/0 0.0291 0.0335 [5184] 0.0945 0.936, −1.295

C31.91H35.78Br0.04N4Ni 537.51 sealed tube, 0.71073 tetragonal I41/a 90(2) 14.5118(14) 14.5118(14) 12.1201(12) 90 90 90 2552.4(6) 4 1.399 0.856 1139 0.05 × 0.07 × 0.11 21509 2127/91/0 0.0550 0.0340 [1794] 0.0810 0.470, −0.354

C31.95H35.88Br0.02N4Zn 543.29 synchrotron, 0.7749 monoclinic P21/n 90(2) 4.8780(3) 12.2044(8) 21.0452(13) 90 96.0452(13) 90 1244.74(14) 2 1.450 1.329 573 0.03 × 0.03 × 0.10 31732 7491/178/0 0.0394 0.0430 [5777] 0.0982 0.734, −0.626

Note: ⎧ ∑ [w(F 2 − F 2)2 ] ⎫1/2 ∑ ||Fo| − |Fc|| o c ⎬ R1 = ; wR 2 = ⎨ 2 2 ∑ |Fo| ⎩ ∑ [w(Fo ) ] ⎭

Table 3. Selected Structural Parameters for Porphyrin Component nonplanar deformation mode mean out-of-plane displacement, Å core dimensions, N---N, Å M−N, Å

Co(Etio-I)

Ni(Etio-I)

Zn(Etio-I)

C70·Ni(Etio-I) ·2C6H6

C70·Ni(OEP)·2C6H6

wave 0.0233(8) 3.9483(15) 3.9560(15) 1.9780(8) 1.9742(7)

saddle 0.1691(13) 3.907(2)

wave 0.0318(10) 4.0751(17) 4.0797(18) 2.0375(9) 2.0398(9)

ruffle 0.3053(11) 3.8596(16) 3.8607(16) 1.9309(11) 1.9312(11) 1.9314(11) 1.9307(12)

dome 0.0502(10) 3.9112(13) 3.9180(13) 1.9576(9) 1.9599(9) 1.9545(9) 1.9586(9)

1.9545(11)

are isostructural. While it is tempting to suggest that the P1̅ M(OEP) and M(Etio-I) systems are isostructural, the cell parameters are sufficiently different to prevent this claim. Although the loss of four CH3 groups dictates the difference between OEP and Etio-I, it produces a nontrivial consequence crystallographically.

porphyrin---fullerene van der Waals contacts. With fullerene structures of Ni(OEP), all eight ethyl groups are usually oriented toward the cage. In the Ni(Etio-I) case, four points of contact, four ethyl groups, are now methyl groups. It was then reasonable to attribute the cage disorder and ineffective cocrystallization to the lack of these particular dispersion forces. However, we found that there are still a large number of fullerene---H atom contacts because Etio-I porphyrin is not symmetrically cupping to the fullerene, rather it shifts to the side. An observation made when comparing M(OEP) with M(EtioI) pristine crystal structures is that the metal porphyrins reside on crystallographic special positions.15,21−23,28−31 A list of late transition metal porphyrins (OEP and Etio-I) and their space groups are provided in Table 4. With the exception of one polymorph of Ni(OEP) and Ni(Etio-I), the remaining metal porphyrins reside on centers of inversion. The Ni(OEP) polymorph and Ni(Etio-I) structures belonging to the tetragonal space group I41/a reside on 4̅ special positions. The P1̅ M(OEP) series are isostructural. Of the M(Etio-I) series, only Co and Cu

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CONCLUSIONS A comparison of the porphyrins Ni(Etio-I) and the often-used Ni(OEP) as cocrystallizing agents for fullerenes suggests that the latter is far superior as an agent that suppresses disorder and affords ready crystallization. The ruffled deformation of the porphyrin core in Ni(Etio-I) from the C70 cocrystal is likely to result from a combination of factors that include the occurrence multiple dispersion and van der Waals interactions. Such deformation has been shown to occur in porphyrins with axial coordination, and to be sensitive to the steric bulk of meso substituents.32 The energy involved was computed to be less than G



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by a bromide substituent. In the Co(Etio-I) mass spectral analysis, a signal corresponding to free-base etioporphyrin-I with the bromine impurity was detected (C30H33N4Br). Thus, it was determined that the etioporphyrin-I starting material contained this bromine impurity. It was confirmed by the manufacturer that Br2 was utilized during its synthesis. Multiple purification attempts by fractional crystallization, recrystallization, and column chromatography did not eliminate the impurity. The mass spectral assignments are corroborated with the crystal structures in this report. Ni(OEP) that was purchased did not show this impurity. Crystal Growth. C70·Ni(Etio-I)·2C6H6. Black blocks of C70·Ni(EtioI)·2C6H6 were obtained by layering an equimolar benzene solution of C70 over a benzene solution of Ni(Etio-I). These cocrystals grew concomitantly amidst purple octahedral crystals of pristine Ni(Etio-I). Both types of crystals were characterized by X-ray diffraction. C70·Ni(OEP)·2C6H6. Black blocks of C70·Ni(OEP)·2C6H6 were obtained by layering an equimolar benzene solution of C70 over a benzene solution of Ni(OEP). Ni(Etio-I). Purple octahedral crystals suitable for X-ray diffraction of Ni(Etio-I) were obtained in two ways. They can be directly produced via recrystallization in toluene, benzene, dichloromethane, or chloroform. Alternatively, crystals of the compound grow concomitantly during the cocrystallization experiments. Co(Etio-I) and Zn(Etio-I). Red needles of Co(Etio-I) or Zn(Etio-I) can be produced in a similar fashion to Ni(Etio-I), either by direct recrystallization in the solvents listed above or they form concomitantly during cocrystallization experiments. Physical Measurements. Mass spectral data were obtained on a Bruker ultrafleXtreme MALDI-TOF/TOF spectrometer. Sample solutions were spotted directly without the use of a matrix. Spectra were collected in positive and negative modes. Crystal Structure Determinations. A red needle of Co(Etio-I) was mounted in the 100 K nitrogen cold stream provided by an Oxford Cryostream low-temperature apparatus on the goniometer head of a Bruker D8 diffractometer equipped with an ApexII CCD detector on beamline 11.3.1 at the Advanced Light Source (Lawrence Berkeley National Laboratory, Berkeley, CA). A red needle of Zn(Etio-I) was mounted on the same system at beamline 11.3.1, however the CCD detector was replaced with a PHOTON 100 CMOS detector. Data were collected with the use of synchrotron radiation (λ = 0.77490 Å). Crystals of Ni(Etio-I) (purple prism) and C70·Ni(OEP)·2C6H6 (black block) were mounted in the 90 K nitrogen cold stream provided by a CRYO Industries low-temperature apparatus on a Bruker ApexII CCD instrument equipped with a molybdenum fine-focus sealed tube. (λ = 0.71073 Å). A black block of C70·Ni(Etio-I)·2C6H6 was mounted similarly on a Bruker D8 DUO also employing Mo Kα radiation (λ = 0.71073 Å). All data sets were reduced with the use of Bruker SAINT,35 and a multiscan absorption correction was applied with the use of SADABS.31 Structure solutions and refinements were conducted with SHELXS-200836 and SHELXL-2014,37 respectively. Crystallographic data are reported in Tables 1 and 2.

Figure 10. Views along the porphyrin planes of pristine Ni(Etio-I) (top), Ni(Etio-I) found in C70·Ni(OEP)·2C6H6 (middle), and Ni(OEP) found in C70·Ni(OEP)·2C6H6 (bottom). Thermal contours are drawn at the 50% probability level and hydrogen atoms are omitted for clarity.

Table 4. Space Group Assignments for M(OEP) and M(EtioI) Crystal Structures metal

OEP

Etio-I

Co Ni

P1̅ (ref 24) I41/a (ref 21) P1̅ (ref 22) P1̅ (ref 23) P1̅ (ref 25) P1̅ (ref 27)

P1̅ I41/a I41/amd (ref 15)

Cu Zn

P1̅ (ref 26) P21/n

10 kcal/mol. The relative orientations of the C70 and Ni(Etio-I) molecules in C70·Ni(Etio-I)·2C6H6 is considerably different from the usual cupping of fullerenes by Ni(OEP) as shown in Figure 5. Also, due to the ruffling, the back-to-back nickel porphyrin interaction does not occur in the structure of C70·Ni(Etio-I)· 2C6H6.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01449.

EXPERIMENTAL SECTION

Additional figures and numbering schemes for the porphyrin crystal structures (PDF)

Materials and General Consideration. Etioporphyrin-I was purchased from Frontier Scientific with 95% purity. M(Etio-I) (M = Co, Ni, Cu, Zn) were prepared according to literature methods by reaction of the corresponding metal acetates with free-base etioporphyrin-I.33,34 Ni(OEP) was purchased from Frontier Scientific with 95% purity. C60 and C70 were purchased from SES Research with 99.5% and 99% purity, respectively. Solvents were obtained commercially and used as received. In addition to the parent M(Etio-I) mass spectral signal for C32H36N4M (M = Ni, Zn), an impurity corresponding to the formula C30H31N4BrM was observed. In this impurity an ethyl group is replaced

Accession Codes

CCDC 1436786−1436790 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. H



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Article

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AUTHOR INFORMATION

Corresponding Authors

*(M.M.O.) E-mail: [email protected]. Telephone: (530) 752-6668. FAX: (530) 752-8995. *(A.L.B.) E-mail: [email protected]. Telephone: (530) 7520941. FAX: (530) 752-2820. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Advanced Light Source, supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract DE-AC02-05CH11231, for beam time and a fellowship to K.B.G., the National Science Foundation for financial support (Grant CHE-1305125 to A.L.B. and M.M.O.), the Department of Education for a GAANN fellowship to X.B.P., and S.Y. Chen for experimental assistance.

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REFERENCES

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