Thermotropic phase transitions in 5,15=bis (4-alkoxyphenyl )octaalkylporphyrins Ernst J. R. Sudholter,*" Marinus van Dijk," Cees J. Teunis," Georgine M. Sanders,"Sybolt Harkema,b Gerrit M. H. van de Velde,' Pieter G. Schoutend and John M. Warmand a Wageningen Agricultural University, Laboratory of Organic Chemistry, Dreijenplein 8, 6703 HB Wageningen, The Netherlands bUniversity of Twente, Laboratory of Chemical Physics, PO Box 21 7, 7500 AE Enschede, The Netherlands 'University of Twente, Laboratory of Inorganic Materials Science, PO Box 217, 7500 AE Enschede, The Netherlands dDelft University of Technology, IRI, Radiation Chemistry Department, Mekelweg 15, 2629 JB Delft, The Netherlands Nineteen novel alkyl substituted porphyrins have been synthesized and their thermal phase behaviour has been investigated in detail.Twelve compounds showed a reversible phase transition below the isotropization temperature. From time resolved microwave conductivity (TRMC) measurements and powder X-ray diffractometry it was concluded that the molecular packing does not change significantly at the lower phase transition temperature and that the porphyrin cores occupy isolated positions. Single X-ray diffraction measurements showed that the porphyrins are arranged in a layered structure and that the space between the layers is occupied by the alkyl substituents of the pyrrole units. The phase transitions at the lower temperature were therefore identified as changes in the crystal ordering of the porphyrins. Self-organized systems of porphyrin molecules are of prominent interest in the study of energy-transfer and electron-transfer processes, for improving our understanding of the photosystem in plants and for the development of new advanced molecular materials with special photophysical properties.Our current research is directed towards the fundamental and more applied problems of photovoltaic organic solar cells based on porphyrin dye molecules, which are deposited on wide bandgap semiconductor materials, like Ti02 and SnO,. In our approach, the self-assembly process of the porphyrin molecules is directed in different ways, i.e. (1) by using amphi- philic porphyrins, orientation can be obtained at an air-water interface and the organized porphyrins can be transferred to the substrate by the Langmuir-Blodgett technique;' (2) by introduction of alkyl substituents at the periphery of the porphyrin core, it might well be possible to introduce calamitic or discotic liquid crystalline properties in a given temperature range;2 (3) by introduction of additional ligating groups to the porphyrins, able to complex transition-metal ions, coordi- nation type dimers, trimers etc.may be ~btained.~ In this contribution we describe our study on the synthesis and phase characterization of two series of alkyl substituted porphyrins. The aim of the research is to correlate phase behaviour and molecular structure. In contrast to phthalocyan- ines, little work has been performed on the mesomorphic properties of porphyrins.' The first report on mesomorphic properties of porphyrins came from Goodby et aL4 In a very narrow temperature traject of only 0.1 "Ca monotropic discotic phase was identified for bis( hydrochlorides) of uroporphyrins.In addition copper containing 5,15-bis( 4-alkoxypheny1)octa- methylporphyrins have been investigated5 and these com-pounds do not possess mesomorphic properties. This is in contrast to a report from Bruce et ~l.,~~who identified a crystal smectic B phase for zinc containing 5,15-bis(4-alkoxyphenyl)-porphyrins. For some tetraalkoxyphenylporphyrins meso-morphic phases were reported on account of calorimetric data; these phases were not identified.6b Gregg et al. reported an extensive study on octaester-substituted porphyrins and their zinc derivative^^^ and on metal containing octakis(alkoxyethy1) p~rphyrins.~"These compounds do form discotic liquid crystalline phase^.^ Recently, Shimizu et aL8 reported that on model to predict mesophase formation. In this model separate disordering temperatures of alkyl side chains and rigid cores determine the existence of mesophases in alkyl-substituted disk-like molecules.Results Synthesis Two series of alkyl-substituted porphyrins have been synthe- sized and characterized by their phase behaviour as a function of temperature. In one series (compounds 1-9) the number of carbon atoms n of the alkoxy chain has been varied between i, PTS, MeOH-CH&12 ii, DW, THF R R Scheme 1 Compound number (n,m): 1 (1,4) 5 (9,4) 9 (18, 4) 13 (8, 5) 17 2 (6,4) 6 (10,4) 10 (8, 1) 14 (8, 6) 18replacing the alkyl substituent in 5,10,15,20-tetrakis(4-alkyl-pheny1)porphyrins by an alkoxy chain, the discotic lamellar 3 (7, 4) 7 (12,4) 11 (8, 2) 15 (8,8) 19 phases (DL)disappeared.Collard and Lillyag propose a simple 4 (8,4) 8 (16,4) 12 (8, 3) 16 (8, 12) J. Muter. Chem., 1996,6(3), 357-363 4-Zn 5-Zn 6-Zn 1 and 18 with a fixed substitution pattern on the pyrrole nngs consisting of a methyl and a butyl group (rn=4) In the other series (compounds 10-16) the length of the alkoxy chain (n=8) has been kept constant and rn, the number of carbon atoms on the pyrrole alkyl group, has been varied between 1 and 12 In addition three Zn-metallated porphynns (compounds 17-19) have been prepared and Characterized The new compounds have been prepared from the correspond- ing 2,2’-methylene dipyrroles and 4-alkoxybenzaldehydes, according to the method described before lo The compounds have been purified by chromatography and characterized by mass spectra, ‘H NMR spectra and elemental analysis Differential scanning calorimetry and hot-stage polarization microscopy The phase transition temperatures and enthalpy changes have been determined by differential scanning calorimetry (DSC) and the data obtained are displayed together with the calcu- lated entropy changes (ASIR)in Table 1 Increasing the length of the alkoxy substituent from n=l to 18 with constant m=4 shows a decrease of the phase transition temperature to the isotropic phase (Fig 1, Table 1) For several compounds (1, 2, 4, 5, 6, 8) additional phase transitions at lower temper- ature have been observed All these transitions are rever-sible Inspection of these samples by hot-stage polarization microscopy did not show significant textural changes on passing through this lower phase transition temperature and the appearance of the material remained solid Increasing the length of the pyrrole alkyl substituent from rn =1 to 12 with constant n =8 also shows a decrease of the phase transition temperature to the isotropic phase (Fig 2, Table 1) In this senes the additional phase transitions at lower temperature (compounds 4, 10-13) are again reversible, no textural changes could be detected by hot-stage polarization microscopy, and the material remained solid (Plate 1) Metallation of some porphynns with Zn2 (compounds+ 17-19) shows a small increase of the phase transition tempera- ture to the isotropic phase For 17 and 18 no lower phase transition temperature was observed, while for 19 the lower phase transition temperature was found at 60°C The phases present between the lower phase transition and Table 1 Phase transition temperatures, enthalpies and entropies of 5,15-bis(4-alkoxyphenyl)-2,8,12,18-tetraalkyl-3,7,13,17-tetramethylporphyrins crystal-isotropic crystal-cry stal compound n m C-tI T/”C AH/kJ mol-’ AS/R c-+c T/”C AH1 kJ mol AS/R metal-free 1 1 4 308 42 87 233 6 14 2 6 4 234 53 12 4 51 3 13 3 7 4 234 52 12 2 - - - 4 8 4 214 52 12 9 77 12 42 5 9 4 192 55 14 2 19 15 60 6 10 4 170 38 102 147 22 62 7 12 4 161 51 140 - - - 8 16 4 120 27 81 70 9 31 113 41 12 7 9 18 4 115 82 25 2 - - - 10 8 1 286 45 96 202 20 50 11 8 2 285 64 13 8 8 6 24 12 8 3 246 63 14 6 83 19 64 4 8 4 214 52 12 9 77 12 42 13 8 5 191 32 82 180 19 50 14 8 6 187 70 18 4 - - - 15 8 8 170 63 170 - - - 16 8 12 143 83 23 9 - - - Zn-metallated 17 8 4 220 46 11 2 - - - 18 9 4 213 41 10 2 - - - 19 10 4 197 39 100 60 5 18 400, 1 200 2 200 yI-* * 100 0 I 0 2 4 6 8 10 12 14 m Fig.2 Phase transition temperatures of 5,15-bis(4-octyloxyphenyl)-octaalkylporphynns (n=8) as a function of alkyl chain length (m) 0,to the isotropic liquid phase, 4,lower phase transition temperature 358 J Muter Chem, 1996, 6(3), 357-363 Plate 1 Textures of compound 4 between crossed polarizers at (a)50 "C and (b) 150"C the phase transition to the isotropic state have been investi- gated in more detail using powder X-ray diffraction measure- ments and time resolved microwave conductivity measurements (TRMC). Powder X-ray diffraction measurements Compounds 4, 6, 8, 10, 12 and 13 have been investigated by X-ray diffractometry at different temperatures. Typical diffractograms are given for 4 at 50 and 95 "C(well below and above the lower phase transition temperature, which is observed at 77 "C; Fig.3). No drastic changes or broadening of the diffraction lines could be observed on passing the lower phase transition temperature, either for this compound or for the other compounds investigated. Special attention was paid to the tegion around 28=20", corresponding to distances of d z4.5 A (corresponding to porphyrin-porphyrin stacking dis- tances)," but no significant changes could be monitored. These observations strongly indicate that, on passing through the lower phase transition temperature, little change in the molecu- lar packing occurs and the ordering in the intermediate phase is very similar to the ordering in the original solid state.Time resolved microwave conductivity measurements (TRMC ) In the TRMC experiments, a small uniform concentration (<lOpmol dm-3) of electron-hole pairs is produced by a nanosecond duration pulse of high-energy (3 MeV) electron radiation. A fraction of the initial electron-hole pairs escape rapid geminate recombination and if they are mobile they result in a reduction in the microwave power reflected by the Fig. 3 Powder X-ray diffractogram of 4 at (a) 50 "C and (b)95 "C sample. This reduction in power is directly related to the radiation induced conductivity, AD." For compounds 1 and 4 the time resolved conductivities per unit absorbed dose (Ao/D) are shown in Fig.4 with the result obtained from octakis(2- nony1oxyethyl)porphyrin.l' It is clear that for the former compounds the observed signal is about 30 times smaller than for the latter and the lifetimes of the transients are very much shorter.The end-of-pulse conductivity per unit absorbed energy (Aa/D), is 9.8 x and 4.2 x low9S m2 J-l for compounds 1 and 4, respectively. The (Aa/D),, values are related to the sum of mobilities of the hole and electron charge carriers [Cp=p(-)+p(+)] and to the average energy required to produce one electron-hole pair E, by (AC/D)~=Cp/E,,." Using a value of E,=25 eV yields a lower limit to the sum of xmobilities: for 1 Xp~2.45 m2 V-' s-' and for 4 Zp> 1.05 x lo-' m2 V-' s-'. This is to be compared with Zp>9 x m2 V-' s-' for the octaalkoxyethyl compound. Upon increasing the temperature of compound 4 and passing its lower phase transition temperature at 77"C, the Aa/D transient does not change significantly.This suggests that only minor changes in the packing of the porphyrin molecules occur. This is consistent with our observations on the tempera- J. Mater. Chem., 1996, 6(3),357-363 359 5 I I I 11' 4t 11 1 n 0 50 loo 150 200 250 timdns Fig. 4 Dose-normalised radiation induced conductivity transients observed on pulsed ionization of solid samples A pulse width of 10 ns was used for the octaalkoxyethyl compound (0)and of 50 ns for the other two samples, compounds 1(0)and 4 (i-t),whose signals have been multiplied by a factor of 10 ture dependent powder X-ray diffraction on this sample The small values observed for (AcT/D)~and Xp for compounds 1 and 4 compared with the much higher values observed for octakis(2-nonyloxyethy1)porphyrinare probably due to the large centre-to-centre distance !etween the porphyrin mol- ecules For 4 a distance of 10 3 A within a layer was observed (vide znfra) In octakis( 2-nonyloxyethy1)porphyrin the macrocycles are arranged ino tilted stacks with a cofacial distance of approxi- mately 34A and a Sentre-to-centre distance in the direction of the stacks of 4 3 A Rapid charge migration has also been observed in stacks of 2,5-didecyloxy- 1,4-be?zoquinone, having a quinone centre-to-centre distance of 4 2 A l2 Single crystal X-ray diffraction For compounds 4 and 2 the single crystal X-ray structures have been resolved (Fig 5 and 6, respectively) Both structures contain half a molecule in the unit cell, the other half being generated by a centre of symmetry The alkoxy chain of compound 4 is in the extended zig-zag conformation The alkoxy chain of compound 2 also shows a (less perfect) extended conformation, with some disorder as is evident from the high values of the thermal parameters in this part of the molecule Adjacent butyl groups of compound 4 show an alternating orientation with respect to the nngs, in contrast with compound 2 where a non-alternating orientation is found The porphyrins are packed in a layered structure [see Fig 5(c) and 6(c)] and the space between the layers is filled with the alkyl chains connected to the pyrrole units Within a given layer the porphynns are Fot in close contact The centFe-to- centre distance is 103A for compound 4 and 9 8A for compound 2 The space above and below the porphyrin core within a layer is occupied by the alkoxyphenyl units, and the phenyl groups interact perpendicularly with the neighbouring porphyrin core Such an interaction is quite common in porphynn lattices l3 Discussion In the series of alkyl-substituted porphyrins investigated, we have shown that increasing the alkyl chain length decreases the phase transition temperature to the isotropic phase Many of the compounds studied also show a reversible lower phase transition temperature The TRMC measurements indicate that charge migration is not affected by passing this phase transition temperature and that it is much lower than the charge migration observed in stacks of octakis( 2-nonyloxy- 360 J Muter Chem, 1996, 6(3), 357-363 Fig. 5 Single crystal X-ray structure of 4 (a) individual molecule, (b) side view within a layer, (c) top view Fig.6 Single crystal X-ray structure of 2 (a) individual molecule, (b)side view within a layer, (c) top view ethy1)porphynn This indicates that in our system the porphy- rin cores are not in cofacial contact and occupy a more isolated position both above and below the lower phase transition temperature Such a structure is supported by the results obtained from single crystal X-ray diffraction measurements, Table 2 Yields, elemental analyses and parent peaks in the FD mass spectra for compounds 1-19 c (Yo) H (Yo) N (Yo) compound yield (TOT calc.found calc. found calc. found mlz 1 67 80.75 80.56 8.28 8.42 6.97 6.94 802 2 49 8 1.47 8 1.47 9.18 9.31 5.93 5.88 942 3 50 81.59 81.42 9.33 9.46 5.76 5.94 97 1 4 54 81.71 81.66 9.48 9.67 5.60 5.53 998 5 35 81.81 81.98 9.61 9.80 5.45 5.52 1027 6 62 81.91 81.86 9.74 9.78 5.30 5.17 1054 7 34 82.10 82.13 9.97 10.10 5.04 4.89 1110 8 71 82.42 82.32 10.37 10.44 4.57 4.42 1224 9 53 82.57 82.30 10.55 10.39 4.38 4.16 1280 10 23 79.26' 79.22 8.34' 8.38 6.57b 6.54 83 1 11 37 81.22 81.33 8.86 9.09 6.32 6.33 887 12 38 81.48 81.53 9.19 9.42 5.94 5.94 942 13 49 81.92 81.64 9.74 9.91 5.31 5.26 1054 14 73 82.11 81.99 9.97 10.12 5.04 4.91 1110 15 77 82.43 82.66 10.38 10.68 4.58 4.56 1224 16 13 82.93 82.92 11.00 11.18 3.87 3.84 1447 17 75.61' 75.56 8.60' 8.79 5.17' 4.96 1061 18 74.26d 74.20 8.58d 8.80 4.91d 4.64 1089 19 74.97" 74.80 8.77" 9.07 4.82" 4.62 1117 a The yields have not been optimized. With 0.25 mol of dichloromethane.'With 0.25 mol of dichloromethane. With 0.6 mol of dichloromethane. " With 0.5 mol of dichloromethane. supplemented by the results from powder X-ray diffraction. The single crystal X-ray experiments showed that the porphy- rins are located in layers and that the space between the layers is filled by the more disordered butyl chains and methyl groups connected to the pyrrole units.It might be expected that by passing the lower phase transition temperature this disorder increases. However, since the powder X-ray diffractometry results showed only very small changes and no broadening of the diffraction lines we come to the final interpretation that in the alkyl substituted porphyrins investigated reversible crystal- crystal and crystal-isotropic liquid transitions occur. Conclusions (1)Increasing the number of carbon atoms in the alkoxy or alkyl-substituted porphyrins, decreases the phase transition temperature to the isotropic liquid phase. (2) Subsequent incorporation of zinc in the porphyrin raises this phase trans- ition temperature.(3) Passing the lower phase transition temperature does not significantly change the molecular pack- ing of the porphyrins, as deduced from TRMC measurements on 4 and powder X-ray diffractometry on 4, 6, 8, 10, 12 and 13. (4) The porphyrin cores occupy isolated positions, as deduced from the absence of rapid charge migration in 1 and 4. (5) The porphyrin molecules in the solid state (2 and 4) are arranged in a layered structure. The space between these layers is occupied by the methyl and butyl groups connected to th? pyrrole unit. The porphyrin centre-to-centre distance is 10.3A for 4 and 9.8 A for 2. (6)Reversible crystakrystal and crystal- isotropic liquid phase transitions have been identified. Experimental The 'H NMR spectra were recorded on a 200MHz Bruker AC 200E spectrometer. All spectra were measured as CDCl, solutions.Field desorption mass spectra were measured on a MS 902equipped with a VG ZAB console. General procedure for the synthesis of the 4-alk ylox ybenzaldehydes A mixture of 4-hydroxybenzaldehyde (0.2 mol), l-bromoalkane (0.25 mol), anhydrous potassium carbonate (0.3mol; dried at 140 "C) and butan-2-one (150cm3) was refluxed with stirring for 20 h. To the cooled reaction mixture diethyl ether (200 cm3) was added and the inorganic salts were filtered off and washed with diethyl ether. The washings were combined with the filtrate and the solvent was evaporated in uucuo. The residue was purified: the aldehydes with alkyl chains up to n= 12 by distillation at 0.1-0.01 mmHg and the aldehydes with n= 16 and n= 18 by chromatography over silica gel, eluent light petroleum (bp 60-80"C)with gradual addition of ethyl ace- tate up to 5%.Average yield 70%. All aldehydes have been described in the 1iterat~re.I~ Synthesis of the 3,3'-dialkyl-4,4-dimethyl-2,2'-meth ylenedipyrroles The synthesis of the 2,2'-methylenedipyrroles (previously denoted as bispyrrolylmethanes) with methyl, ethyl and butyl as the variable alkyl substituent has been described in a previous publication."" The other 2,2'-methylenedipyrroles were prepared in a completely analogous way. The dipropyl- and the dihexyl-methylenedipyrroles have been described in the literat~re.~~?~~ The dipentyl-, dioctyl- and the didodecyl- methylenedipyrroles are rather unstable; they were charac-terized by their 'H NMR and mass spectra and used without further purification for the synthesis of the porphyrins.General procedure for the synthesis of the 2,8,12,18-tetraalkyl- 5,15-bis(4-alkyloxypheny1)-3,7,13,17-tetramethylporphyrins To a solution of 3,3'-dialkyl-4,4-dimethyl-2,2'-methylenedipyr-role (10mmol) and 4-alkyloxybenzaldehyde (10mmol) in methanol (200 cm3) and dichloromethane (50 cm3), toluene-p- sulfonic acid (0.5 g) was added. The mixture was stirred for 4h at room temperature and left overnight in the refrigerator. The solvent was removed below 40°C and the residue was dissolved in tetrahydrofuran (250 cm'). A solution of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone(4.2 g) (DDQ) was added over a period of 5 min and the mixture was stirred for 1 h at room temperature.After evaporation of the solvent in U~CUOthe residue was dissolved in dichloromethane (50 cm3), the insoluble material was filtered off and the filtrate was diluted with methanol-triethylamine, 3 : 1 (250cm3). Upon cooling to 0°C a precipitate was formed, which was filtered off and washed with methanol-dichloromethane, 9 : 1. The crude product thus obtained was purified by chromatography over silica gel (Merck Kieselgel 60,0.040-0.063 mm), eluent J. Mater. Chem., 1996, 6(3), 357-363 361 dichloromethane with gradual addition of 1-2% methanol. The yields varied between 7 and 73%, average yield 45%.The conversion of free base porphyrins into their zinc derivatives'* is quantitative (100%). The yields, elemental analyses and mass spectral data are shown in Table 2.f 'H NMR spectra of the compounds 1-19. A typical example is the 'H NMR spectrum of compound 4: &-2.45 (2 H, brs, NH), 0.93 (6 H, t, CH3 $-Octyl), 1.07 (12 H, t, CH3 a-butyl), 1.37 (16 H, m, CH, G,&,(,q-octyl), 1.70 (12 H, m, CH, y-butyl, y-octyl), 1.98 (4 H, m, CH2 p-octyl), 2.14 (8 H, m, CH2 p-butyl), 2.52 (12 H, S, CH3), 3.96 (8 H, t, CH2 a-butyl), 4.24 (4 H, t, CH2 a-octyl), 7.24 (4 H, d, 3 H-, 5 H-phenyl), 7.90 (4 H, d, 2 H-, 6 H- phenyl), 10.20 (2 H, s, 10 H-, 20 H). The other compounds had similar spectra differing only in the alkyl part of the spectrum.The integration values were in agreement with the expected values. Phase transition measurements DSC measurements were performed on a Perkin-Elmer DSC- 7 system. Optical inspection of the samples was carried out between crossed polarizers of an Olympus BH-2 polarization microscope which was equipped with a Mettler FP82 HT hot- stage, controlled by a Mettler FP 80 HT central processor. Pulse radiolysis time resolved microwave conductivity The powder samples were contained in a microwave cell consisting of a piece of rectangular Q-band wave guide of cross section 7.1 x 3.55 mm2 closed at one end with a metal plate and fitted with a wave guide flange at the other. Approximately 200mg of material was compressed by hand into the cell using a close-fitting Teflon plunger.The length and mass of the sample were measured. The samples were ionized by irradiation with a pulse of 3 MeV electrons from a Van de Graaf accelerator. The pulse duration could be varied from 0.2 to 50ns. The precise conditions of irradiation and energy deposition have been presented before." The energy deposition is close to uniform throughout the sample and accurately known. Changes in the conductivity of the sample on irradiation are monitored as changes in the microwave power reflected with nanosecond time resolution. By monitoring the signals over the frequency band available of 26.5 to 38 GHz the absolute value of the radiation-induced conductivity could be determined and related to the total dose (in J m-3) absorbed by the sample during the pulse to give the dose normalised conductivity, Ao/D, which is plotted as a function of time in Fig.4. Powder X-ray diffraction Samples of about 20mg of the porphyrin compounds were put into a small (0.5 cm diameter) depression of a Pt-Rh sample carrier and smoothed to a flat surface. The platinum carrier strip also functioned as a connection between anode and cathode for heating purposes. The high temperature chamber surrounding the carrier was a Biihler HDK 1.4, mounted on the 8 axis of a Philips goniometer PW1050, automated with a stepping motor, graphite monochromator, counter and Windows operating and analysing software of Sietronics Sie Ray 122D. Divergence and receiving slits were both 1.0 mm.Scans were done in air, usually between 10 and 60" 28, with a scan velocity of 2 or 1" min-l and scan step of 0.02". t For the zinc derivatives of the porphyrins and for compound 10 we had to assume the presence of 0.25-0.6 mol of CH,Cl, per mol of porphyrin. The tendency of porphyrins to include solvent molecules, which are difficult to remove, has been described before (see ref. 10). 362 J. Muter. Chem., 1996, 6(3), 357-363 Single crystal X-ray diffraction The most important crystallographic data are collected in Table 3. Only small crystals could be obtained in the form of thin needles. Therefore only a limited number of significant reflections could be measured, resulting in a rather low obser- vation to parameter ratio.Data were collected in the 01-28 scan mode [scan width (w): 1.0+0.4 tan SO], using graphite monochromated Mo-Ka radiation. The intensity data were corrected for Lorentz and polarization effects and for long time scale variation. No absorption was applied. The structure was solved with MULTAN17 and refined by full-matrix least-squares. Weights for each reflection in the refinement (on F) were w= 4FO2/a(Fo2), with a(Fo2)=02(1)+(PF,~)~;the value of the instability factor p was determined as 0.04. All calculations were done with SDP." Atomic scattering factors were taken from International Tables for X-ray Crystal10graphy.l~ In both structures the asymmetric unit contains one half molecule; the other half is generated by a centre of symmetry.Positions and thermal parameters of the non-hydrogens were refined anisotropically. To keep the number of variables in the refinement small, hydrogen atoms were put in calculated positions and treated as riding atoms. Positions for hydrogens of the methyl groups attached to the rings, which could not be calculated, were found from difference Fourier syntheses and were subsequently refined. In both structures the N-H hydrogen atom could neither be found from difference Fourier synthesis, nor could the position be deduced from the geometry around the nitrogen atom. Consequently the N-H hydrogen atom has not been included in the calculations. Both structures show disorder in some part of the molecule, Table 3 Crystallographic data compound 4 2 C68H94N402 C64H86N402 Mr 999.5 943.4 crystal system triclinic t riclinic sp$ce group Pi Pi 44 10.302 (4) 9.828 (2) b/+ 11.609 (5) 11.490 (2) c/A 14.451 (6) 13.805 (6) aldegrees 106.53 (4) 105.35 (2) PJdegrees 105.77 (4) 104.60 (2) y/degrees 100.12 (4) 100.54 (3) V/A3 1533 (3) 1401 (2) z 1 1 1.082 1.117DX/wyP3P/mm -0.60 0.62 T/K 293 (1) 293 (1) crystal size/mm3 0.50 x 0.10 x 0.02 0.40 x 0.15 x 0.02 data collection: radiation Mo-Ka Mo-Ka /degrees 22.5 25.0emax refl.measured 3989 491 1 refl. obs I >3a(I) 1696 1375 h range -13+13 -11411 k range -1444 -13+13 1 range -17+0 0416 refinement: final R 0.065 0.060 Rw 0.074 0.059 S 2.17 1.34 observations 1696 1375 parameters 359 341 0.02 0.20(A/4max APmaxle 4-33 0.19 0.27 Aprnin/e A--0.26 -0.17 as evidenced by the large thermal parameters of some atoms.In compound 2 disorder is found in one of the two independent butyl groups. In compound 4 the alkoxy chain shows some disorder. In both cases bond lengths and angles are affected by the disorder. Atomic coordinates, bond lengths and angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre. For details of the deposition scheme, see ‘Information for Authors’, J. Muter. Chem., 1996, Issue 1. 8 9 10 111, 3024; (b) B. A. Gregg, M. A. Fox and A. J. Bard, J. Phys. Chem., 1989, 93,4227; (c) B. A. Gregg, M. A. Fox and A. J. Bard, J. Phys. Chem., 1990, 94, 1586; (d) B. A. Gregg, M. A. Fox and A. J. Bard, J.Chem. SOC., Chem. Commun., 1987,1134. (a) Y. Shimizu, M. Miya, A. Nagata, K. Ohta, I. Yamamoto and S. Kusabayashi, Liq. Cryst., 1993,14,795;(b)Y. Shimizu, M. Miya, A. Nagata, K. Ohta, I. Yamamoto and S. Kusabayashi, Chem. Lett., 1991, 25; (c) Y. Shimizu, A. Ishikawa, S. Kusabayashi, M. Miya and A. Nagata, J. Chem. SOC., Chem. Commun., 1993,656. D. M. Collard and C. P. Lillya, J. Am. Chem. SOC., 1991,113,8577. G. M. Sanders, M. van Dijk, A. van Veldhuizen, H. C. van der Plas, U. Hofstra and T. J. Schaafsma, J. Org. Chem., 1988,53, 5272. The authors wish to thank Mr. H. Jongejan for performing the elemental analyses and Mr. A. van Veldhuizen for the NMR measurements. 11 12 (a)P. G. Schouten, J. M. Warman, M. P. de Haas, M. A. Fox and H. L. Pan, Nature, 1991, 353, 736; (b) P. G.Schouten, J. M. Warman and M. P. de Haas, J. Phys. Chem., 1993,97,9863. E. M. D. Keegstra, P. G. Schouten, A. Schouten, H. Kooijman, A. L. Spek, M. P. de Haas, J. W. Zwikker, J. M. Warman and L. W. Jenneskens, Red. Trau. Chim. Pays-Bas, 1993,112,423. References 13 (a) M. P. Bym, C. J. Curtis, Y. Hsiou, S. I. Khan, P. A. Sawin, S. K. Tendick, A. Terzis and C. E. Strouse, J. Am. Chem. SOC., 1993, J. M. Kroon, E. J. R. Sudholter, A. P. H. J. Schenning and R. J. M. Nolte, Langmuir, 1995,11,214. (a) D. W. Bruce, in Inorganic Materials, ed. D. W. Bruce and D. OHare, Wiley, New York, 1992, ch. 8; (b) J. M. Kroon, P. S. Schenkels, M. van Dijk and E. J. R. Sudholter, J. Mater. Chem., 1995,5, 1309. 14 15 115, 9480; (b) M. P. Byrn, C. J. Curtis, I.Goldberg, Y. Hsiou, S. I. Khan, P. A. Sawin, S. K. Tendick and C. E. Strouse, J. Am. Chem. SOC., 1991,113,6549. G. W. Gray and B. Jones, J. Chem. SOC.,1954,1467 and references cited therein. J. L. Sessler, J. Hugdahl and M. R. Johnson, J. Org. Chem., 1986, (a) A. M. Brun, S. J. Atherton, A. Harriman, V. Heitz and J.-P. Sauvage, J.Am. Chem. SOC., 1992, 114,4632; (b)R. Schrijvers, M. van Dijk, G. M. Sanders and E. J. R. Sudhblter, Red. Trau. Chim. Pays-Bas, 1994,113,351. J. W. Goodby, P. S. Robinson, B.-K. Teo and P. E. Cladis, Mol. Cryst. Liq. Cryst., 1980,56, 303. S. Gaspard, P. Maillard and J. Billard, Mol. Cryst. Liq. Cryst., 1985,123,369. 16 17 18 51,2838. T. Nagata, A. Osuka and K. Maruyama, J. Am. Chem. SOC., 1990, 112,3054. G. Germain, P. Main and M. M. Woofson, Acta Crystallogr., Sect. A, 1971,27,368. B. A. Frenz and Associates Inc. (1983), Structure Determination Package, College Station, Texas, and Enraf-Nonius, Delft, The Netherlands. (a) D. W. Bruce, D. A. Dunmur, L. S. Santa and M. A. Wall, J. Mater. Chem., 1992, 2, 363; (b)S. Kugimiya and M. Takemura, 19 International Tables for X-ray Crystallography, Kynoch Press, Birmingham, England, 1974,vol. IV. Tetrahedron Lett., 1990,31, 3157. (a)B. A. Gregg, M. A. Fox and A. J. Bard, J. Am. Chem. SOC., 1989, Paper 5/04588F;Received 12th July, 1995 J. Mater. Chem., 1996, 6(3), 357-363 363