Jameson, Ibers
1 5,I O , I 5,2O- [ Pyrromellitoyl(tetrakis-o-oxyeth~.~yphenyl)]porph~~rin
2823
Structure of the Free-Base “Capped” Porphyrin, 5,10,15,20[Pyrromellitoyl( tetrakis-o- oxyethoxyphenyl)]porphyrin Geoffrey B. Jameson and James A. hers* Contribution f r o m the Department of Chemisirj>,Northwestern Unioersity, Ecanston. Illinois 60201. Receired Augusi 8, I979
Abstract: The structure of the free-base, “capped” porphyrin 5, IO, 1 S,20-[pyrromellitoyl(tetrakis-o-oxyethox~phenyl)]porphyrin (H2Cap) has been determined by three-dimensional, single-crystal, X-ray diffraction methods using diffractomcter data collected with Mo K O radiation. The material crystallizes as the pentachloroform, monomethanol solvate, H2Cap. SCHCII-CH~OH,in space group C2hS- P21/n with four formula units in a cell of dimensions (at -150’ C) n = 19.947 (6) A, b = 16.569 (5) A, c = 22.602 (7) A, p = 104.57 (I)’, V = 7230 A3,The structure was described by 495 variable parameters and at convergence the values for R and R, (on F, 8552 data having Fo2> 3a(FO2))were 0.073 and 0.094. In contrast to most other free-base porphyrins, the 24-atom porphyrin skeleton is markedly nonplanar (mean displacement from the least-squares plane 0.1 35 A; maximum displacement 0.354 A), but conforms closely to idealized D2d symmetry. The considerable steric strain involved in attaching a pyrromellitoyl(tetrakisoxyethoxy) “cap” to the ortho positions of the tetraphenylporphyrin core is released most obviously through buckling of the porphyrin skeleton. The transannular separation between aminopyrrole nitrogen atoms is 4.182 (6) A; between imino nitrogen atoms it is 4.038 (5) A, The separations between the centroids of the phenyl “cap” and respectively those of the four pyrrole nitrogen atoms and the 24-atom porphyrin skeleton are 3.86 and 3.96 Aresults of considerable interest in relation to the ligand binding properties of iron(I1) and cobalt(1l) derivatives of H2Cap.
Introduction Model systems have been widel) studied in attempts to understand better the structure-function relationships of oxygen-binding hemoproteins, such as myoglobin and hemoglobin.’-6 O f the well-characterized model systems used, only t h e iron( 11) derivatives of the “picket-fence’’ p ~ r p h y r i n , ~ HzTpivPP,? and of the “capped” porphyrin*-’O (see Figure 1) exhibit reversible uptake of dioxygen to give dioxygen complexes stable a t ambient temperatures.” Both these porphyrins, derivatives of 5,10,15,20-tetraphenylporphyrin(H2TPP), have bulky ortho substituents which create a protected site, analogous to that provided by the protein, where small molecules such as 0 2 , C O , and N O m a y bind to t h e metal center. T h e “capped” porphyrin system possesses several inherent a d vantages over the much more extensively studied “picketfence” porphyrin, chief of which is that binding of a second axial base, such as 1 -methylimidazole, the usual synthetic analogue for histidine of t h e hemoglobins, is either prevented completely in the case of Fe(Cap)( I - M e I m ) or severely hindered in the case of F e ( H m C a p ) ( I-MeIm).’O Whereas the stereochemistries of a number of “picket-fence’’ porphyrin derivatives have been d e f i n e d , l ~ ’ ~no - ’ precise ~ structural data have yet been obtained for t h e “capped” porphyrin. The cap of the “capped” porphyrin is conformationally more rigid in contrast to t h e rather flexible “pickets” of t h e “picket-fence’’ porphyrin-crystallographically a highly desirable feature. Furthermore t h e 24-atom porphyrinato skeleton generally is essentially planar (mean displacement typically less t h a n 0.03 A) for the conformationally flexible porphyrins, not only in the free-base form (for example, H2TPrP,15 porphine,16 H 2 0 E P , I 7 H 2 M P I X D M E , I 8 and H 2 P P I X D M E l 9 ) but also in their metallo derivatives.l S o m e notable exceptions a r e N i ( 0 E P ) in t h e tetragonal form,*O where marked ruffling of the porphyrinato skeleton is associated with unusually short M-Nporph bond lengths, H 2 T P P in both the triclinic2Ia and tetragonal and Fe(TPP)(2-MeIm), where unusually large doming of the porphyrinato skeleton is attributed to crystal packing forces.’ Other metallo derivatives of H z T P P have essentially planar porphyrinato cores. These porphyrins all lack substituents which could supply internal constraints to force t h e porphyrin to adopt a nonplanar configuration seen in the highly substituted mesosubstituted octaethylporphyrins.22 0002-78631801 l502-2823$01 .OO/O
For deoxyhemoglobin it has been calculated23 that the protein envelope enforces a nonplanar conformation upon the heme group. Consequently, studies of t h e ligand affinities of the “capped” porphyrin model system, where internal constraints m a y prevent a planar porphyrin geometry, coupled with comparison of such a system with the less constrained model systems based upon TPP or TpivPP, m a y shed light on the interaction of hemoglobin with small molecules. T h e first base binding and the dioxygen binding properties of iron(l1) and cobalt(l1) derivatives of “capped” porphyrins’O a r e very different from those of analogous complexes of T P P and better these differences provides a T ~ ~ V PTo P understand . ~ ~ ~ compelling reason for determining the crystal and molecular structure of the free-base porphyrin, H 2 C a p S C H C l 3 C H 3 0 H , the first “capped” porphyrin compound that we have thus far been able to crystallize. Experimental Section Preparation of H ~ C ~ ~ S C H C I ~ * C H JThe O Hfree-base . porphyrin in powder form was kindly supplied by Professor J. E. Baldwin. Over the period of 1 year very large crystals were obtained by solvent diffusion at 5’ C of methanol into a chloroform solution of HzCap. On the basis of density measurements (see below) and thermogravimetric analysis for loss of solvent the formulation of these crystals is H2CapSCHCI3CH30H. Crystallographic Study of H2CapSCHCI3CH30H. Solvate loss occurs rapidly when crystals are exposed to air at room temperature. Symmetry and systematic absences consistent with the monoclinic space groups C2h - C2/c or Cs4- Cc were observed by precession and Weissenberg photography of a crystal sealed in a capillary. Cell constants at room temperature are a = 20.18 A, b = 16.81 A, c = 22.92 A, p = 105.2’, V = 751 1 A3. The calculated and observed densities were 1.472 and 1.47 ( I ) g respectively. The crystal selected for data collection upon a Picker FACS-I automatic diffractometer was chipped from a large crystal. During the cooling to approximately - 150 ‘C for data collection, the crystal underwent a phase change to space group C2hS - P 2 1 / n , presumably a consequence of an increased ordering of the solvate molecules. Reflections of the type hkl where h k is odd were still systematically weak but were observable. Crystal quality was apparently unaffected by the phase change since crystal mosaicities (peak width at half peak height as determined using w scans) were typically in the range 0.12-0.19° Lattice parameters at -150 ‘C were obtained, as previously described,24by the hand centering of 19 reflections in the range 0.4030 < X-I sin 8 < 0.4468 A-l (33.22’ < 28 < 36.95’) using Mo Kal
+
0 I980 American Chemical Society
2824
Journal of the American Chemical Society
/ 102.8 /
April 9, I980
Table 1. Crystal Data and Data Collection Procedures for H2Cap 5C H CI 3.C H 3 0 H
formula formula weight, amu space group a.
A
h, A c*
A
13, deg
v,A3
-ten-sided lump, -0.90
Z temp crystal shape
crystal volume, radiation
150 O C "
1111173
linear abs coeff, cm-I transmission factors detector aperture take-off angle, deg scan speed A-1 sin 6 limits, A-1 background counts scan range data collected
P unique data, including systematic absences unique data with FO2> 3'J(Fo2) a
C68H53CI I 5N401.3 1665.99 CZh5 - P21/n I9.947(6) 16.569(5) 22.602( 7) 104.57( 1 ) 7230 4
X 0.57 X 0.50 A; principal bounding faces, {TI I),IlOOl 0.206 graphite-monochromated MO Ka, A ( K N I )0.7093 A 6.10 0.74-0.76 (no correction made) 5.3 mm wide, 5.0 mm high, 32 cm from crystal 3.0 2.0' in 28 per min 0.043 1-0.5790 (3.5' < 26 (Mo K a l ) < 48.5') I O s at each end of scan, with rescan option I , I O below K a l to I .Oo above Ka2 ih,k,l 0.05 1 1 565
8552
The low-temperature system is based on a design by Huffman,
J . C. Ph.D. Thesis, Indiana University, 1974. Lenhert, P. G. J . Appl. Crystallogr. 1975,8, 568-570.
"Capped" porphyrin molecules: (a) x = 2, HzCap; (b) x = 3, HzHmCap. The four chains linking the phenyl "cap" to the tetraphenylporphyrin moiety are identical. Figure 1.
radiation (A = 0.7093 A). Other important featuresofdata collection are summarized in Table I . The structure was solved using the M U L T A N 7 8 program. In the resultant E map, 100 atoms (i.e., almost all atoms) of the porphyrin and solvate species appeared. Standard procedures and programs24 were used to develop and refine this structure, with the Northwestern University CDC6600 computer being used initially and the Lawrence Berkeley Laboratory CDC7600 computer for the final stages. Atoms in phenyl groups were constrained to D 6 h geometry ( c - c = 1.395 A), although in the final stages of refinement the constraints on the phenyl "cap" were removed. Isotropic refinement of the model led to values for R and R , on F , of 0.180 and 0.236, respectively. The thermal parameters of the solvate molecules were now allowed to vary anisotropically, and further refinement of the model lowered the values for R and R, to 0.105 and 0.139. In the difference Fourier synthesis which followed, despite large peaks around two of the five chloroform
T
I
2i64~c,151
Cli4)
Solvate-8
Sdvote-C
Cl681-
Solvate-D
003)
kthmol
Figure 2.
Atom labeling scheme for H2CapSCHC13CH30H.
solvate molecules, all hydrogen atoms, except for the hydroxyl hydrogen atom of the methanol nlolecule, were observed and included at their idealized positions in subsequent structure-factor calculations as a fixed contribution to F,. One disordered chloroform molecule (chloroform E) suffered a rotational disorder about the C-H bond. For another, chloroform A, alternative sites existed such that one CI atom was common to both sites. Figure 2 illustrates the disorder and defines the atom labeling scheme for the porphyrin and solvate molecules. The minor components were granted only isotropic thermal parameters. The final model was described by 495 variable parameters, including parameters describing the occupancies of the solvate molecules. Upon refinement the final values for R and R, were 0.073 and 0.094. The standard error in an observation of unit weight is 2.5 1 e. For chloroform A the total occupancy is 0.931 (4), apportioned 0.730:0.201 (4) between the major and minor components. For solvate E the occupancy of the major component is 0.772 (7) and of the minor 0.148 (7). For this solvate molecule, because of near superposition of chlorine positions and because of probable disorder in the carbon atom position, which is inferred from its abnormally high thermal parameters, the estimated standard deviations in bond distances and angles derived from the inverse of the least-squares matrix are grossly u n derestimated. The occupancies of chloroform solvate molecules B, C, and D are 0.853 ( 3 ) ,0.899 (3). and 0.926 (3). respectively. The occupancy for the methanol solvate molecule is 0.906 ( I O ) . The apparent departures of the chloroform solvate molecules from the full occupancies of 1 .O expected from density and thermogravimetric measurements may arise from the inadequacies of the anisotropic model, or any other model, to cater adequately for unresolved disorder. These inadequacies are reflected in the residual electron density which is concentrated around the chloroform solvate molecules with a highest peak of 0.93 ( I O ) e A-3, Values for the minimized function are independent of the magnitude of F,; there is a slight dependence on the magnitude of A-' sin 6 with very low angle data (A-' sin 6 < 0.269 A-I) returning a higher value. In view of the phase transition from C 2 / c or Cc to P21/n it is comforting that no dependency upon any combination of Miller indices could be found. Full anisotropic refinement was not carried out because of the expense involved with minimal expectation of dramatic changes in porphyrin parameters from these low-temperature data. Final nonhydrogen parameters are listed in Tables I 1 and 111. Hydrogen
2825
Jameson, Ibers / 5,10,15,20-[ Pyrromellitoj~l(tetrakis-o-oxyethoxyphenyl)]porphyrin Table II. Positional and Thermal Parameters for H2Cap.SCHC13CH30H
....~.*. d1OM
P
I
2
7
RII
OR
t)rA
822
833
012
913
023
.........**..,........*...*.**.*..........*........*...*...*..*~*..*.****..*..~***~~***~**~.~**~..****~~.*..U...*.."
0.5051 31 I U )
0.1972481761
38.69 (691
29.47 1741
16.92142)
2.26153)
CL121
-0.3428PllZl
0.49 8 1 I I1 2 I
9.780151131
14.35161
22.49t851
30.72(77)
-2.28157)
CLIII
0.04R2J119'Il
)
C L I1 I
0 9 1 05 I , I I1 1 I
0.~Y9191121
0.3253971921
2h.01 (70)
27.07(901
16.39(511
-3.81160)
CC(4I
O.llhCY81841
U.L'"4l7iIII
0.6607501751
15.az(4ai
40.93(05)
15.20(401
0.221501
CL15l
0.?54'91lIlul
0.U713911Ul
U.5809L121791
35.791691
20.53168)
l7.30(431
0.06(531
C L I ~ I 0.74uhlO(791
lJ.23551 I I U I
0.5 36478 < 781
14.16t471
29.78 1751
19.911451
-1.561451
C L 171
O.Q.'1795
0.506991121
J.470112192I
16.381521
49.62 199)
28.26 (561
CLIBI
0.7n37b11~1
8 . 4 0 2 IY II2 )
0.4531091961
42.514811
38.63 (921
25.97(561
ELI91
0.OR97ht>(991
~.5L71IIIIl
0.414902198)
27.11163)
27.38t791
3*.32(611
CLllOl
0.1'~70291Q91
0.4Y57RI141
0.0437581961
15. 05 I50 I
67.5112)
30.79(5*)
I.15lbll
CL111l
0.301070~921
0.565441111
b.091171 1761
28-61 (591
33.83 (791
17.91(43)
-5.88153)
IRH)
1 a24 I55 I
-15.78(671
4.50154)
CLIIO
u.mn71111
0 . 4 1 6 9 8 II
II
0.0244141921
41.42 1761
28.68177)
29.18(56)
10.07159)
CL113)
0.5Q7USl2.71
0.1Y9161181
0.74537115)
96.3 II8 I
13.91101
15.50 171 I
-0.1 t 101
CL I 1 41
0.44751 121 I
0.353RRI201
0.73654 I391
41.81 15)
32.4(131
CL 1151
0.59288 122)
0.34676
0.789651151
3h.9118)
40.8114)
37.24 (951
C1631
0.034951391
0.535221421
0.26722(371
17.1(23)
12.61281
23.3(221
-2.2(?01
Cl6l,I
0.?4707~3?1
0.1734.11371
0.59991130)
13.81191
19.3(251
l6.4(171
-3.7(181 -9.5121)
8 I81
-0.2 I I I I
Il6.2(381
-4. I I I 1 I
C1651
0.73504135)
0.499701411
0.471111301
21.1 I211
42.2 1331
l4.01161
Cl66l
0.255IR(371
0.47422 I 4 u l
0.074lbl291
ia.2(201
34. I I291
l6.1(16)
0.2(19)
C1671
0.513a3161)
0.300361591
0.74493158)
73.01551
39.7 I 4 2 I
69.7 (531
-0.5(30)
0.073931311
-O.I026l(20)
21.4(16)
50.71261
I7.l(121
5.011b)
4.09741 1331
28.9 127 I
45.51391
20.4120l
0.7125)
01131
-O.?41I81231
C I ~ R I -0.2711114ni
0. I5Olhl48l
CL 121'
-0.097021401
0.495021531
0.17399(40)
4.34 123)
ATOM .~
CLIJI'
-0.016l4(9hl
0.5US11101
O.Z961Y(771
6.a91421
C1271
-0.27781 1281
0.
I I752 (331
0.7 3275 (241
........................................*......*..**.*......* V
I
e
2.761101
C~113l'
0.4h415(671
0.35750178)
0.69581 (501
1.031281
Ct281
-0.?5053(261
O1O3306(3U1
0.74054122)
I .94 (91
CL1141
0.54549164)
0.35417 (631
0.79936 I461
6.68 I301
0 121
-0.18038( I71
0.U30631201
0.7327YI151
2.03161
,
0.2U97~101
0.73374 (75)
3. I8 I321
C1291
-0.129691241
0.V53871291
0.779961211
1-71 19)
0.53131191
0.22431141
2.851581
0131
-0.137551171
0.07039121)
0.830201l5l
2.37(71
-0.09152(191
o.~187n8(231
0.78513(17)
1.4817)
0141
0.n~3511l71
0.19795091
0.540451151
1-91161
-0,ORR57(251
0.299741291
0.845751221
1-66(9)
C1361
0.05356(261
0.12195130)
0.51704 122)
1-96 ( 9)
c12I
-0.157721241
0.311991291
0.850061r?l)
1-77191
C(371
-0.0183912Sl
O.ll2I4130I
0,52681 (22)
1.88191
COI
-0.200061251
0.JU6881291
0.7930Y(22)
1.95191
0 15 I
-0, II 1h76 II6 I
0.11608119)
0.590931141
1.73(6)
c 141 c 151
-0.15859 ( 2 4 )
0.29 I54 1281
9.75112(211
I.5l18l
ti381
0.005271241
0.05014(28)
0.62321121)
1.62191
-0. I a235 (241
0.28563(28)
0.68753(21l
1.65181
0161
O.O1971(17l
-0.01250(211
0.602641151
2.20(7)
NI2l
-O.S7IUY(19)
0.29203123)
0.65967 ( 1 1 I
1.6117)
0 17 I
0.25688 t 181
0.17057(21)
0.19413115)
2.2017)
Cl6l
-0.14116124l
0.284701281
u.64555121)
1.5918)
C145l
0.29436127)
0.096851321
0.80210(231
2.29 IIO1
C
-0.16984 (251
0.2839R
0.57991(22)
I .85 191
C1461
0.25351126l
0.03891130l
0.75563123)
2.10(91
Cl8l
-0.11624125)
0.292921291
0.55495(221
1.76191
0181
o.in3911171
0.0323412Ul
0.7631U115l
2.00(6)
C191
-0.054541241
CL 1151'
0.51606177)
c1611
-O.~?261161
NIII
Clll
(71
1291
0.291531281
u.60463(211
1-61 ( 8 )
C147)
0.13348124)
0.U6493178)
0.71924(211
1.71(9)
C ( Io1
0. u I2 38 (241
0.30890(28)
0.59695(21)
1.61191
0191
0.140901191
0.09262(211
0.67197(151
2.40(71
N131
0.075YUIL91
0.295941221
0.70507117)
1.48171
01131
-0.097821171
0.19U40IPO)
0.95274(15)
2.1217)
CIIII
0.07218(231
0.3U982128l
0.64439(211
1.53(81
C154l
-O.O626l(2hl
0.1 1770 13U)
0.97821 (23)
2.18110)
Cll?I
O.ISl711251
0.12552(291
0.640051221
1.85191
C 1551
0.1)1048(2hl
0.11372131)
0.97064123)
2.13110l
C I 131
0. I 4 4 3 4 ( 2 4 1
0.319981291
0.696531211
1-81 ( 9 1
OIIII
0.01037117l
0.1 1636 ( 7u)
0.90h7l(15l
1.9716)
t( 1 4 I
0.14328 123)
0.30189128)
0.73857120)
1.4418)
t 156 I
-0.00084 1241
0.047241791
0.8768712Il
1,7119l
C (151
0 . I6743(24J
0.295421781
0 .e0194 (21I
I .5R 18)
0112)
-0.on6651181
-0.01734121)
0,89875116)
2,20(7)
-0.OhI78(251
N14I
0.055461191
0.2Y337122)
0.829991 171
1.47171
CIS71
Ci I h l
0. I263512Jl
0.290691?8)
0.84347121)
1.53101
~ ( 5 8 1 -o.0'~28(21,)
t1171
0.15413(25)
0.2n8701?9)
0.90945 1221
1.83(91
c 1591
c ( IR I
0. I . I 1 35 12s I
u.29ino(mi
U .93544 1221
1.8519)
~1631
0.ulR601241
0.2'9654 I 2 8 1
0.88495(211
1-67 191
Cl61l
0.062381241
0.30257129)
O.R9314(2ll
1.72191
C167l
-0.000131241
0.14651~2Il
0.676571161
2.57(71
C1191 Ct2vl
-0.32Ql
(241
-o.?7051(181
0.05671)1301
0.76464 (PPI
1.8Rt9)
0.0595nt281
0.70360 121 I
1.69(9)
o.on447 124)
0.06n1~178)
Q.SR~II(ZI)
lr67(91
0.06614 ( 2 4 1
0.06157128l
0.7?5sn1?11
1.60191
0.061 85 1791
0.79602181)
I.80(9)
0.057~117~1
~ . R I O ~ O I ? I I 1.59(8)
................................................................................................................................. n(ii
Estimated standard deviations in the least significant figure(s) are given in parentheses in this and all subsequent tables. The form of the anisotropic thermal elliposid is: exp[-(5, lh2 + 522k2 5 3 J 2 -t251zhk + 25l3hI + 25&/)]. The quantities given in the table are the thermal coefficients x IO4.
A
+
atom parameters are given in Table I V . 2 5 Table V lists the value of 1O1F0Ivs. l O I F J . 2 5
Description of the Structure and Discussion General Information. T h e crystal structure consists of dis-
Crete monomeric molecules o f t h e "capped" porphyrin, HzCap, a s illustrated in Figure 3, immersed in a matrix of solvate molecules with S(CHCl3):l(CH~OH):l(H~Cap). T h e molecular connectivity of H z C a p is t h a t expected.8 Hydrogen bonding of the methanol and interactions of some of t h e
-0.25931 I l l 1
0.20896l18)
0.66189I15l
0.244091111
0.361701171
-0.28971 115)
0.36257 1 151
0.64020 (161
0.27150114l
0.374@9l111
-0.36I20(16)
0.36773 (1 61
0.61671 116)
0.34265 (15)
0.381381 IS1
-0.402461 I?)
0.29927(20)
0.61490117)
0.38638 1 1 I 1
0.31630lI9)
-0.372061151
0.22566 (16)
0.636591171
0.35897l141
0.243911161
-0.300491161
0.22050114)
0.660081151
0.28783(15)
0.23662114) 0.315141181
0 -321691 I81
0.53328(101
- 0 . 0 3 6 3 6 ( 17)
0.39011~171
0.50018 1141
-0.009421171
0.38SOI(17)
- 0 . 0 0 0 ~ 0 1181
0.400961l6)
0.44060(131
-0.01761 I181
0.39877~I 61
0.03370(18)
0.34339120)
0.41428(111
-0.05276 (191
0.34266 1701
0.06166I17l
0.27498(171
0.44738 (131
-0.079701171
0.020631171 -0.00734
( 17)
0.272781181
................................................................................................................................... 0.50688(131
0.2641131151
0.05513l161
-o.o7lsl~lT~
0.2S902(151
R I G I D GROUP PIRAMETCRS A
1
....................................................~..~~~*......~.~~......~......~............~~..*..~...........
6ROUP
7
Y
X
C
C
PH-I
-0.33009(111
PH-2
0.0771611Ol
PH-3
0.31574
