Piguet and coworkers investigated the thermal behavior of 5,50- and 6,60- substituted 2,6-bis(1-ethyl-benzimidazol-2-yl)pyridines and the corresponding lanthanide complexes [RL(NO3)3] or [RL(CF3SO3)3] (Escande et al., 2010;
Piguet et al., 2006; Terazzi et al., 2006a). The 5,50-substituted ligands L16–L19 are shown in Fig. 45 and the 6,60-substituted ligands L20–L23in Fig. 46. The first reported ligands had two terminal alkyl chains, that is, one dodecyloxy chain at both end of the molecules. Conformational changes (trans–trans!cis–cis) occur upon complexation to lanthanide ions: the I-shaped 5-substituted ligands are transformed into U-shaped lanthanide com- plexes, whereas the U-shaped 6-substituted ligands give I-shaped lanthanide TABLE 13 Thermal Behavior of the Nematogenic Lanthanideb-Diketonate Complexes Shown inFig. 44
Lanthanide R CnH2nþ1 Temperatures (C) Reference
La CH3 Cr 252 I Dzhabarov et al. (2010)
La C2H5 Cr 133 SmA 146 N 160 I Dzhabarov et al. (2010) La C3H7 Cr 106 N 136 I Dzhabarov et al. (2010) La C4H9 Cr 74 SmA 102 N 142 I Dzhabarov et al. (2010) La C5H11 Cr 76 SmA 94 N 134 I Dzhabarov et al. (2010) La C6H13 Cr 73 SmA 89 N 138 I Dzhabarov et al. (2010) La C7H15 Cr 64 SmA 98 N 132 I Dzhabarov et al. (2010)
g 64 SmA 98 N 132 I Galyametdinov et al. (2008) Nd C7H15 g 74 SmA 106 N 140 I Galyametdinov et al. (2008) Eu C7H15 g 72 SmA 108 142 I Galyametdinov et al. (2008) Yb C7H15 g 76 SmA 101 134 I Galyametdinov et al. (2008) La C8H17 Cr 74 SmA 93 N 132 I Dzhabarov et al. (2010) Cr, crystalline phase; g, glass; N, nematic phase; SmA, smectic A phase, I, isotropic liquid.
complexes (Fig. 47;Nozary et al., 2000). The 5-substituted 2,6-bis(benzimi- dazol-2-yl)pyridines are calamitic LCs and exhibit a rich mesomorphism (SmC, SmA and/or N). Although it was initially reported that the lanthanide complexes show essentially the same mesomorphism as the ligands (Nozary et al., 1997a), further studies showed that the lanthanide complexes have a low thermal stability and are not mesomorphic (Nozary et al., 1997b, 1998).
N N
N N
N
O O
O O
C12H25O OC12H25
N N
N N
N
O O
C12H25O OC12H25
N N
N N
N
O O
O O
O O
O O
C12H25O OC12H25
N N
N N
O N O
C12H25O OC12H25
Cr 144 SmA 193 I Cr 131 SmC 217 SmA 223 N 226 I
Cr 107 I
Cr 206 SmX 280 N 322 I L15
L16
L17
L18
N N
N N
N
O O
O O
C12H25O OC12H25
C12H25O
C12H25O
OC12H25
OC12H25
L19 Cr 25 Colh61 I
FIGURE 45 5,50-Substituted 2,6-bis(1-ethyl-benzimidazol-2-yl)pyridines and their transition temperatures (in C).Abbreviations: Cr ¼ crystalline phase, SmC ¼smectic C phase, SmA
¼smectic A phase, N¼nematic phase, Colh¼hexagonal columnar phase, I¼isotropic liquid.
N N
N N
N
O O
C12H25O OC12H25
N N
N N
N
O O
C12H25O OC12H25
C12H25O OC12H25
L20
L21
N N
N N
N
O O
O O
C12H25O
C12H25O OC12H25 C12H25O OC12H25 OC12H25
L23
Cr 154 I
Cr 74 I
Cr 58 I N N
N N
N
O O
O O
O O
C12H25O OC12H25
L22 Cr 195 Colr203 I
FIGURE 46 6,60-Substituted 2,6-bis(1-ethyl-benzimidazol-2-yl)pyridines and their transition temperatures (inC).Abbreviations: Cr¼crystalline phase, Colr¼rectangular columnar phase, I¼isotropic liquid.
banana LCs. However, no mesomorphism was detected. The corresponding lanthanide complexes have the shape of calamitic LCs, but they decompose at temperatures between 180 and 200C, without evidence for mesomorph- ism. The absence of mesomorphism was attributed to the spatial expansion brought by the bulky R(NO3)3groups (Nozary et al., 2002). Two of the three bound bidentate nitrate anions are located on opposite sides of the planar aro- matic core, so that they strongly disturb the intermolecular interactions between the rigid cores and reduce the molecular anisotropy. Also a ligand with four terminal chains (L21) did not lead to liquid-crystalline lanthanide complexes (Nozary et al., 2000).
Liquid-crystalline lanthanide complexes could be obtained by increasing the number of terminal alkyl chains to six, that is, the complexes of ligands L19andL23(Fig. 48;Terazzi et al., 2003, 2005). These hexacatenar ligands contain peripheral gallic acid residues with dodecyloxy chains. Interestingly, the type of mesophase depends on the lanthanide ion, and the minor contraction of about 15% on going from La3þto Lu3þis sufficient to cause a change of mesophase behavior from lamellar over cubic to columnar.
The hemidisk-shaped complexes [R(L19)(NO3)3] exhibit a sequence of lamella-columnar (Lcol) and body-centered cubic mesophases for large lantha- nide(III) ions (R¼La–Nd), a body-centered cubic mesophase (Cub,Im3m) for the mid-sized lanthanide ions (R¼Sm–Ho) and a hexagonal columnar phase for the small lanthanide ions (R¼Er–Lu; Terazzi et al., 2005). When ligand L19 was modified by reversing the esters spacers (benzimidazole-COO- phenyl instead of benzimidazole-OOC-phenyl), the corresponding lanthanide complexes were not liquid-crystalline (Terazzi et al., 2007). This example shows the subtle relationship between molecular structure and the formation of mesophases. Density functional theory (DFT) calculations showed that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strand of the ligand. The mesophase behavior of the [R(L23)(NO3)3] complexes is very similar to those of [R(L19)(NO3)3] complexes, except that in this case most of the lanthanide complexes (R¼La–Ho) form the lamellocolumnar phase at low temperatures. This points to an improved stabilization of the meso- phases by ligands that form a rod-like geometrical arrangement upon coordi- nation to the R(NO3)3 moiety. For the smaller lanthanide(III) ions, the complexes [R(L19)(NO3)3] and [R(L23)(NO3)3] exists as monomeric build- ing blocks in the solid state and probably also in the mesophase.
The hemidisk-like monometallic complexes are compact enough to induce pyridine–pyridine interactions between head-to-tail tridentate cores, and these interactions are responsible for the formation of the columns of the hexagonal columnar phase. The weak intercolumnar interactions, responsible for the positional order in the hexagonal columnar mesophase, can be attributed to residual interactions involving pairs of appended gallic acid residues. When
N N
N N
N
N N
N N
N
N N
N N
N
N N
N N
N R3+
R3+
R3+
R3+
5
6 5
6
5 6 5
6 Ligand trans–trans
I-shape
Ligand trans–trans
U-shape
Complex cis–cis I-shape
Complex cis–cis U-shape
FIGURE 47 Conformational changes (trans–trans!cis–cis) occurring upon complexation to trivalent lanthanide ions for (A) 5-substituted and (B) 6-substituted 2,6-bis(benzimidazol-2-yl)pyr- idines. Linear substituents have been schematized by rods.
N N
N N
N
O O
O O
C12H25O
C12H25O OC12H25 C12H25O OC12H25 OC12H25 R
N O
O O
3
N N
N N
N
R N O
O O
3
O O
O O
C12H25O C12H25O
C12H25O
OC12H25 OC12H25 OC12H25
FIGURE 48 Structure of lanthanidomesogens [R(L19)(NO3)3] (top) and [R(L23)(NO3)3] (bottom).
intracolumnar interactions becomes weaker. The orthogonal intercolumnar packing occurring between the gallic ester residues with dodecyloxy chains compete with the intracolumnar packing and this leads to an oscillation or puckering of the columns. In the case of oscillations of the columns, disloca- tions are formed and these dislocation points lead to the isotropic growth of the columns in the three Cartesian directions of space, and to the formation of a bicontinuous structure. In the case of puckering of the columns, the cylin- drical rods are pinced off and discrete micelles are formed. The 3D close packing of these soft micelles leads to the formation of a micellar body- centered cubic phase. It is often very difficult to discriminate between cubic bicontinuous and cubic micellar phases, and a detailed study of the XRD pat- terns of the mesophases in combination with molecular modeling is required.
For the larger lanthanide ions the complexes occur as dimers in the solid state and in solution. Therefore, it is assumed that the first mesophase formed upon heating of the complexes of the large lanthanide ions also contain dimers. The existence of the rodlike dimers removes the strong intermolecularp-stacking and a residual lamellar ordering is detected. The complexes [R(L19) (CF3COO)3] form a hexagonal columnar phase at high temperatures, whereas the [R(L23)(CF3COO)3] complexes form a lamellar mesophase (Nozary et al., 2006). The mesophases occur only at high temperatures and they consist of mixtures of complexes, dissociated ligands and metal salts. By attaching 12 peripheral dodecyloxy chains to the central tridentate aromatic binding unit a dodecacatenar ligand L24 is formed (Fig. 49; Escande et al., 2007). The ligand exhibit a mesophase between34 and 56C, but it was not possible to assign the mesophase with certainty as a SmA or to a Colhphase. The lan- thanide complexes [R(L24)(NO3)3] and the dimeric complex [Eu(L24) (CF3COO)3]2are liquid-crystalline at room temperature. The compounds have a remarkably broad mesophase range, sometimes even larger than 250C.
N N
N N
N
O O
O O
C12H25O OC12H25
C12H25O
C12H25O
OC12H25
OC12H25
L24 O
O
O O
C12H25O
C12H25O OC12H25 C12H25O OC12H25 OC12H25
FIGURE 49 Structure of dodecacatenar ligandL24.
These complexes are rare examples of room-temperature lanthanidomesogens.
A series of dendrimeric 2,6-bis(benzimidazol-2-yl)pyridine ligandsL25–L28 have been synthesized (Fig. 50; Jensen et al., 2008, 2010; Terazzi et al., 2006b). The complexes [R(L25)(NO3)3] and [R(L26)(NO3)3] exhibit for the large lanthanide ions (R¼La, Pr) a bilayer smectic mesophase in the temper- ature range between 90 and 180C. Methylation of the terminal cyanobiphe- nyl groups in [R(L26)(NO3)3] leads to the appearance of an additional interdigitated lamellar phase (R¼Gd, Tb, Lu) or a nematic phase (R¼Eu, Y, Lu) with the medium-sized or small lanthanide ions. The introduction of the methyl groups destabilizes the layer-like organization in the smectic A phase at higher temperatures, with the formation of a nematic phase as a result. The complexes [R(L26)(NO3)3] of the heavier lanthanide ions are among the rare examples of nematogenic lanthanidomesogens. No meso- morphism was observed for the complexes [R(L27)(NO3)3] and [R(L28)
N N
N N
N
O O
O O
O O O
O O
O O (CH2)10
(CH)10
(CH2)10 O
O
O O
O O
CN
CN O
O X X
O
X=
L25
O O O
O O
O O (CH2)10
(CH)10
(CH2)10 O
O
O O
O O
CN
CN O
X=
L26
L27 O
O O
O O
O O (CH2)10
O X=
CN
CN
O O O
(CH2)10 O
X= CN L28
FIGURE 50 Dendrimeric 2,6-bis(1-ethyl-benzimidazol-2-yl)pyridine ligandsL25–L28.
with methyl groups on the terminal cyanobiphenyl groups. An overview of the transition temperatures and mesophase behavior of the 2,6-bis(1-ethyl- benzimidazol-2-yl)pyridine complexes is given inTable 14.
The insight obtained by systematically studying the influence of structural changes in the bis(benzimidazol-2-yl)pyridine ligands on the mesophase behavior of the ligands and the corresponding lanthanide complexes with R (NO3)3and R(CF3COO)3groups, inspired Piguet to propose a thermodynamic model to rationalize the formation of thermotropic mesophases in metallome- sogens with a bulky metal core (Escande et al., 2007, 2010; Piguet et al.,
TABLE 14 Thermal Behavior of the Lanthanide Complexes of 2,6-Bis (1-Ethyl-Benzimidazol-2-yl)pyridines Ligands L19, L23, L24, L25, and L26
Complex Temperatures (C) Reference [Pr(L19)(NO3)3] g 125 Lcol175 Cub 249 I Terazzi et al. (2005) [Nd(L19)(NO3)3] g 70 Lcol140 Cub 211 dec. Terazzi et al. (2005) [Sm(L19)(NO3)3] g 130 Cub 180 dec. Terazzi et al. (2005) [Eu(L19)(NO3)3] g 140 Cub>200 dec. Terazzi et al. (2005) [Gd(L19)(NO3)3] g 145 Cub>200 dec. Terazzi et al. (2005) [Tb(L19)(NO3)3] g 155 Cub 205 dec. Terazzi et al. (2005) [Dy(L19)(NO3)3] g 155 Cub 212 dec. Terazzi et al. (2005) [Ho(L19)(NO3)3] g 155 Cub 217 dec. Terazzi et al. (2005) [Er(L19)(NO3)3] g 160 Colh221 dec. Terazzi et al. (2005) [Tm(L19)(NO3)3] g 160 Colh221 dec. Terazzi et al. (2005) [Yb(L19)(NO3)3] g 160 Colh223 dec. Terazzi et al. (2005) [Lu(L19)(NO3)3] g 160 Colh223 dec. Terazzi et al. (2005) [Pr(L23)(NO3)3] g 100 Lcol140 Cub
190 dec.
Terazzi et al. (2005)
[Nd(L23)(NO3)3] g 120 Lcol160 Cub 180 dec.
Terazzi et al. (2005)
[Sm(L23)(NO3)3] g 160 Lcol180 Cub 190 dec. Terazzi et al. (2005) [Eu(L23)(NO3)3] g 120 Lcol180 Cub 190 dec. Terazzi et al. (2005) [Gd(L23)(NO3)3] g 100 Lcol160 Cub 190 dec. Terazzi et al. (2005) [Tb(L23)(NO3)3] g 160 Cub 171 dec. Terazzi et al. (2005) [Dy(L23)(NO3)3] g 90 Lcol180 dec. Terazzi et al. (2005)
TABLE 14 Thermal Behavior of the Lanthanide Complexes of 2,6-Bis (1-Ethyl-Benzimidazol-2-yl)pyridines Ligands L19, L23, L24, L25, and L26—Cont’d
Complex Temperatures (C) Reference [Ho(L23)(NO3)3] g 160 Cub 175 dec. Terazzi et al. (2005) [Er(L23)(NO3)3] g 150 Colh180 Cub 185 dec. Terazzi et al. (2005) [Tm(L23)(NO3)3] g 160 Lcol180 dec. Terazzi et al. (2005) [Yb(L23)(NO3)3] g 175 Colh195 dec. Terazzi et al. (2005) [Lu(L23)(NO3)3] g 155 Colh190 I Terazzi et al. (2005) [La(L24)(NO3)3] Cr25 SmA (or Colh) 110–
130 Cub 240 dec.
Escande et al. (2007)
[Pr(L24)(NO3)3] Cr43 SmA (or Colh) 110–
130 Cub 207 dec.
Escande et al. (2007)
[Sm(L24)(NO3)3] Cr34 Colh208 dec. Escande et al. (2007) [Eu(L24)(NO3)3] Cr31 Colh220 dec. Escande et al. (2007) [Gd(L24)(NO3)3] Cr32 Colh220 dec. Escande et al. (2007) [Tb(L24)(NO3)3] Cr33 Colh214 dec. Escande et al. (2007) [Yb(L24)(NO3)3] Cr32 Colh240 dec. Escande et al. (2007) [Lu(L24)(NO3)3] Cr32 Colh21 dec. Escande et al. (2007) [Y(L24)(NO3)3] Cr35 Colh114 Colh291
SmA 229 dec.
Escande et al. (2007)
[Eu(L24)(CF3COO)3]2 Cr37 Colh139 I Escande et al. (2007) [Pr(L25)(NO3)3] g 80 SmA2 190 dec. Jensen et al. (2010) [Eu(L25)(NO3)3] g 80 SmA 186 I Jensen et al. (2008, 2010) [Gd(L25)(NO3)3] g 85 SmA2 188 I/dec. Jensen et al. (2010) [Tb(L25)(NO3)3] g 90 SmA2 190 I/dec. Jensen et al. (2010) [Lu(L25)(NO3)3] g 100 SmA2 150 PCr 170
SmA2 200 I/dec.
Jensen et al. (2010)
[La(L26)(NO3)3] g 90–110 SmA2 159 I Jensen et al. (2010) [Pr(L26)(NO3)3] g 90–110 SmA2 147 I Jensen et al. (2010) [Eu(L26)(NO3)3] g 100 SmA 138 N 144 I Jensen et al. (2008) g 90–110 SmA2 138 N 144 I Jensen et al. (2010) [Gd(L26)(NO3)3] g 90–110 SmA2 139 SmAd
144 I/dec.
Jensen et al. (2010)
Continued
2006; Terazzi et al., 2006a, 2007). In this qualitative thermodynamic model, it is assumed that a thermotropic liquid-crystalline phase results from the melt- ing of a microsegregated solid, in which the packed polarizable aromatic cores of the molecules are grafted with long, flexible and poorly polarizable alkyl chains. The microsegregation organization corresponds to a minimum in energy in the crystalline solids, because the intermolecular multipolar elec- trostatic interactions between the polarizable aromatic cores are maximized, while the fully extended alkyl chains (in all-transconformation) fill the voids between the aromatic cores. The melting process corresponds to the melting of the packed alkyl chains (hydrocarbon chains). The breaking of the moder- ate intermolecular interactions resulting from the packing of the alkyl chains in the all-trans conformation is largely compensated by the large entropic increase, resulting from the relaxation of the vibrational and rotational degrees of freedom. A thermotropic mesophase can thus be considered as a state of matter made up of clusters of packed semiorganized rigid cores, dispersed in a liquid continuum of molten alkyl chains. The melting temperatureTmis given by the following equation:
TmTmchains¼DHchainsm
DSchainsm , ð12Þ
where DHchainsm is the enthalpy change upon melting, and DSchainsm is the corresponding entropy change. The melting point of LCs is low because the interactions between the poorly polarizable alkyl chains are weak (DHmchains is small) and the release of configurational entropy upon melting is consider- able for the flexible alkyl chains (DSchainsm is large). In first approximation, the melting temperature is rather insensitive to the length of the alkyl chain, becauseDHmchainsandDSchainsm both increase to the same extent upon increasing
TABLE 14 Thermal Behavior of the Lanthanide Complexes of 2,6-Bis (1-Ethyl-Benzimidazol-2-yl)pyridines Ligands L19, L23, L24, L25, and L26—Cont’d
Complex Temperatures (C) Reference [Tb(L26)(NO3)3] g 90–100 SmA2 137 SmAd
144 I/dec.
Jensen et al. (2010)
[Y(L26)(NO3)3] g 90–110 SmA2 134 N 144 I/
dec.
Jensen et al. (2010)
[Lu(L26)(NO3)3] g 90–100 L 130 N 144 I/dec. Jensen et al. (2010) Cr, crystalline phase; g, glass; SmA, smectic A phase; SmA2, bilayer smectic A phase; SmAd, partially interdigitated smectic A phase; N, nematic phase; Cub, cubic phase; L, lamellar phase; Lcol, lamellar-columnar phase; Colh, hexagonal columnar phase; I, isotropic liquid; dec., decomposition.
PCr, re-entrant partially crystallized phase.
the alkyl chain length and the melting temperature is the ratio between these two quantities (Eq. 12). This is the enthalpy/entropy compensation effect.
However, increasing the number of alkyl chains on the rigid polarizable aro- matic core leads to significant deviations from the enthalpy/entropy compen- sation. Lower melting temperatures are produced due to an increase in entropy incompletely balanced by some parallel increase in enthalpy. Further heating of the mesophase produces a second phase transition that is characterized by the clearing temperatureTc:
TcTmcores¼DHcoresm
DScoresm ð13Þ
whereDHmcores is the enthalpy change at the clearing point, andDScoresm is the corresponding entropy change. At the clearing temperature, the rigid polar- izable cores become completely decorrelated and an isotropic liquid is formed.
The phenomena of chain and core melting are not independent in real liquid- crystalline systems. Some loss of cohesion between the rigid cores will already occur at the melting temperatureTmand this partial loss can explain the fluidity of mesophases. This simple model predicts that the introduction of a bulky molecular groups close to the rigid core, such as the R(NO3)3and R(CF3COO)3 groups upon complex formation of the mesogenic ligands with lanthanide(III) nitrate or trifluoroacetate salts, is harmful for the liquid-crystalline properties, becauseDHcoresm decreases to such an extent that the clearing and melting pro- cesses coincide, so that no mesophase is formed. Piguet recognizes four strate- gies to design lanthanidomesogens (Terazzi et al., 2007):
1. Embedding of the R3þions or RX3fragments in a cocoon of wrapped aro- matic rings, to ensure a significant entropic contribution DHmcores to the clearing process. This strategy is found in the phthalocyanine complexes (seeSection 8).
2. Attaching a large number of diverging flexible chains to the central aro- matic binding units in order to give polycatenar ligands with large entropic contributionsDSchainsm , which produce a melting point low enough to pro- mote the formation of a mesophase. This is the most popular approach to obtain lanthanidomesogens with low melting points.
3. Spatially decoupling the rigid aromatic cores responsible for the residual inter- molecular cohesion in the mesophase from the bulky lanthanide unit, preserv- ingDHmcoreslarge enough to give high clearing temperatures.This approach was followed for the complexes of ligandsL25–L28andL49–L51.
4. Tuning enthalpic contributions to the melting and clearing processes (DHmchainsandDHcoresm ) by the judicious design of aromatic rings with oppo- site polarization along the ligand strand. Experiments show thatDHmcoresis more influences by minor changes in the intramolecular stacking interac- tions occuring in the condensed phases (Terazzi et al., 2007).
The first lanthanide-containing metallomesogens described in the literature were the substituted bis(phthalocyaninato)lutetium(III) complexes, which were reported by the research group of Simon in 1985 (Piechocki, 1985; Pie- chocki et al., 1985). In these compounds, the lanthanide(III) ion is sandwiched between two phthalocyanine rings. The structure of these double-decker com- pounds is somewhat similar to that of ferrocene. The phthalocyanines were prepared as part of a search for 1D molecular semiconductors. The conductiv- ity behavior of the unsubstituted bis(phthalocyaninato)lutetium(III) sandwich complexes was already known, but it was not realized previously that aligned columnar mesophases formed by such metallophthalocyanines can be consid- ered as electrical wires at a molecular level, with the molten alkyl chains act- ing as insulating layers. There is a similarity between the molecular arrangement of the phthalocyanine complexes in the columnar mesophase and that of 1D conducting organic crystal. The phthalocyanine ring is one of the most stable macrocycles. Different substitution patterns are possible on the macrocycle ring, but the octakis-substituted phthalocyanines, with eight substituents on the peripheral positions of the phthalocyanine ring, are the easiest to synthesize. Substitution patterns which have been reported for bis(phthalocyaninato)lanthanide(III) complexes are: alkoxy substitution (L29), alkoxymethyl substitution (L30), alkylthio substitution (L31), alkyl substitution (L32), and poly(oxyethylene) substitution (L33) (Fig. 51). A structure of an octakis-alkoxysubstituted bis(phthalocyaninato)lanthanide(III) sandwich complex is shown inFig. 52.
The synthetic routes to the bis(phthalocyaninato)lanthanide(III) complexes can be divided into two general classes: (a) reaction between a metal free phthalocyanine and a lanthanide(III) salt and (b) reaction between phthalocy- anine precursors and a lanthanide(III) salt (template reaction). Piechocki obtained alkoxymethyl-substituted complexes [(CnH2nþ1OCH2)8Pc]2Lu (n¼8, 12, 18) by reaction between the corresponding metal-free phthalocya- nines (CnH2nþ1OCH2)8PcH2 and lutetium(III) acetate, in 1-pentanol at 140C (Piechocki, 1985; Piechocki et al., 1985). In order to form the phtha- locyanine dianion Pc2, a very large excess of potassium pentanolate was necessary (50 times the stoichiometric amount). Before reaction, the lute- tium(III) salt was dissolved in refluxing 1,2-propanediol. During the reaction, first the intermediate product [(CnH2nþ1OCH2)8Pc]Lu(OAc) is supposed to be formed, and subsequently a mixture of the anionic complex [(CnH2nþ1OCH2)8Pc]2LuKþ(blue–green) was formed and the neutral com- pound [(CnH2nþ1OCH2)8Pc]2Lu (green) is formed. The crude reaction mix- ture contained mainly the anionic [(CnH2nþ1OCH2)8Pc]2LuKþ. By treatment of the organic phase with a diluted aqueous solution of hydrochloric acid, the green [(CnH2nþ1OCH2)8Pc]2Lu complex was generated from [(CnH2nþ1OCH2)8Pc]2LuKþ and isolated. The compounds were purified
by flash chromatography on a silica column. The yield of the reaction decreased from 50% to 30% for the octyloxymethyl to the octadecyloctomethyl chain. The red oxidized form ½ðCnH2nþ1OCH2Þ8Pc2Luþ½SbCl6 was obtained by reaction in dichloromethane of [(CnH2nþ1OCH2)8Pc]2Lu with a stoichiometric amount of the mild oxidizing reagent phenoxathiin hexachloroantimonate. This reagent is a radical cation and can be obtained by reaction between SbCl5and phenoxathiin in dichloromethane (Gans et al., 1981).
An alternative synthetic route to these sandwich complexes is atemplate reac- tion. By treatment of 4,5-di(octyloxy)phthalonitrile with R(acac)3nH2O (acac¼acetylacetonate) in the ratio 6:1 using the sterically hindered organic
N HN H2n+1CnO
H2n+1CnO OCnH2n+1 OCnH2n+1
OCnH2n+1 OCnH2n+1 H2n+1CnO
H2n+1CnO
N HN H2n+1CnS
H2n+1CnS
SCnH2n+1 SCnH2n+1
SCnH2n+1 SCnH2n+1 H2n+1CnS
H2n+1CnS
N HN H2n+1CnOH2C
H2n+1CnOH2C
H2n+1CnOH2C
H2n+1CnOH2C CH2OCnH2n+1 CH2OCnH2n+1 CH2OCnH2n+1
CH2OCnH2n+1
N HN
N NH N
NH N
NH N
NH N
NH N HN
CnH2n+1 CnH2n+1
CnH2n+1 CnH2n+1 H2n+1Cn
H2n+1Cn H2n+1Cn
H2n+1Cn
O(CH2CH2O)nCH3 O(CH2CH2O)nCH3
O(CH2CH2O)nCH3 O(CH2CH2O)nCH3 O
O O H3C(OCH2CH2)nO H3C(OCH2CH2)n
H3C(OCH2CH2)n H3C(OCH2CH2)n
L29 L30
L31 L32
L33
FIGURE 51 Overview of different phthalocyanine ligands.