Synthesis and properties of copper (11) and oxovanadium( IV) complexes derived from polar Schiff's bases Eduardo Campillos, Mercedes Marcos, Ana Omenat and Jose Luis Serrano Quimica Orgbnica, Instituto de Ciencia de Materiales de Aragbn, Universidad de Zaragoza-CSIC, 50009-Zaragoza, Spain The synthesis and mesogenic behaviour of copper(I1) and oxovanadium(1v) complexes derived from Schiff 's bases substituted with polar groups and of their corresponding ligands are reported. The polar groups studied are F, CF,, CN, and CH2CN in the 3 or 4 position of the aniline moiety. The ligands exhibited smectic C, smectic A and nematic phases, whereas the complexes showed smectic A and nematic phases, and in some cases oxovanadium(1v) complexes exhibited a smectic crystal phase.Metal complexes of Schiff's bases have played an important role in the development of metallomesogens.' The particular advantage of the salicylaldimine ligand system is the consider- able flexibility of the synthetic procedure which has allowed the preparation of a wide variety of complexes whose properties are strongly dependent on the ligand structure and on the metal used.2 However, little is known about the relationship between the molecular structure and the mesophase behaviour of these compounds. Ovchinnikov et al. have carried out some systematic studies on these kinds of c~mplexes,~-~ while we have described the mesomorphic properties of several series of copper (II), nickel (11) and oxovanadium(1v) complexes derived from N-alkyl and N-aryl salicylaldimines6 and have studied the relationship between mesogenic behaviour and molecular str~cture.~ In these studies we found that the best liquid-crystal properties are obtained with systems derived from 2,4-dihydroxybenzal- dehyde.To improve our knowledge of the relationship between molecular structure and mesogenic properties, we present in this paper the synthesis and the mesogenic properties of several new families of copper(I1) and oxovanadium (~v) complexes derived from imines with lateral and/or terminal polar groups in the amine part with general structure A. Experimental Synthesis The preparation of the ligands and chelates was carried out according to Scheme 1 (series A) and Scheme 2 (series B and C). Synthesis of the Schiff's bases.The free ligands L were synthesized using a well known method' by mixing an ethanolic solution of 1 mmol of the appropriate aldehyde (3 or 7) with 1 mmol of the appropriate amine (4) and 2 drops of acetic acid as catalyst. The precipitated product was purified by recrystallization from ethanol (yields 60-78 %). Synthesis of aldehyde 3.4-Hexyloxy-2-hydroxybenzaldehyde was synthesized as described previouslyg using Williamson's method by reaction of hexyl bromide (2; 1 mmol), with 2,4- dihydroxybenzaldehyde (1) in the presence of KHCO, (1 mmol) as base in acetone. The product was purified by flash chromatography using hexane-thy1 acetate (96 :4) as eluent. Synthesis of aldehyde 7. 4-(4-Decyloxybenzoyloxy)-2-hydroxybenzaldehyde was synthesized by reaction of 4-decyl- oxybenzoyl chloride (6; 1 mmol; synthesized by refluxing for 2 h a solution of 4-alkoxybenzoic acid (5) in SOCl2 and two Y XH \---I A Series A : R = HI3C6O-M=CU Series B : R = C~H,~O-(=J-coo-M = cu, vo Series c : R = c,~H,,o -(J-coo-M = cu, vo X Y Z ligand Cu" complexes V"O complexes F H F 1A 1A-Cu H F H 2A 2A-c~ H CF, H 3A 3A-c~ H CN H 4A 4A-c~ HH CN 5A 5A-c~ HH CH2CN 6A 6A-c~ F H F 1B 1B-Cu 1B-VO H F H 2B 2B-c~ 1B-VO H CF, H 3B 3B-c~ 3B-VO H CN H 4B 4B-c~ 4B-VO HH CN 5B 5B-c~ 5B-VO HH CH2CN 6B 6B-c~ 6B-VO F H F 1c 1c-cu 1c-vo H F H 2c 2c-cu 2c-vo H CF, H 3c 3c-cu 3C-VO H CN H 4c 4c-cu 4C-VO H H CN 5c 5c-cu 5C-VO H H CH2CN 6C 6C-CU 6C-VO drops of DMF] with 2,4-dihydroxybenzaldehyde (1; 1 mmol) in CH2C12 and triethylamine as a base.The product was purified by recrystallization in ethanol. The Schiff bases L and the intermediates were characterized by elemental analysis and IR spectroscopy. Elemental analysis showed that the structures of all the materials are consistent with those expected (Table 1). J. Muter. Chem., 1996, 6(3), 349-355 349 series A series A-Cu Scheme 1 Reagents and conditions (I) KHCO,, acetone, reflux, (11) ethanol, AcOH, reflux, (111) ethanol, reflux 7+ Ln (iv) n= 10 (series C)Ln + Cu(CH3CG) 2H20 -Wbh n= 6 (series 6) series B-Cu n = 6 series C-Cu n = 10 series B-VO n = 6 series C-VO n = 10 Scheme 2 Reagents and conditions (I) SOCl,, DMF, reflux, 3 h, (11) CH,Cl,, Et,N, room temp, (111) EtOH, AcOH, reflux, (iv) EtOH, (v) MeOH, Et,N Preparation of the metal complexes.The synthesis of cop- per@) complexes was carried out as described previously4b by the addition of an ethanolic solution (20 ml) containing copper(I1) acetate [Cu(OAc), -HzO](1mmol) to a hot solution of the appropriate imine (2 mmol) in ethanol (50 ml) Oxovanadium(1v) complexes were synthesized by the addition of a methanolic solution (20 ml) containing vanadium(1v) oxide sulfate (VOS04 5H,O) (1 mmol) in the presence of triethylamine to a hot solution of the appropriate imine (2 mmol) in methanol (50 ml) In both cases the solution was refluxed for 1-2 h After cooling the precipitate was collected by filtration and recrystallized from a mixture of ethyl acetate and ethanol (1 3) The crystals are green for the oxovanadium(1v) complexes and brown for the copper(I1) complexes The elemental analyses and yields of the copper(I1) complexes 350 J Mater Chem , 1996, 6(3), 349-355 are gathered in Table 2, those for the oxovanadium(1v) com- plexes are in Table 3 Techniques Microanalysis was performed with a Perkin-Elmer 2400 mic-roanalyser IR spectra were obtained using a Perkin-Elmer 1600 (series FTIR) spectrophotometer over the 400-4000 cm -' spectral range The textures of the mesophases were studied with an optical microscope (Nikon) equipped wth polarlzed light, a Mettler FP82 hotstage and a Mettler central processor Measurements of transition temperatures were made using a Perkin-Elmer DSC-2 differential scanning calorimeter with a heating or cool- ing rate of 10°C min-' The apparatus was calibrated with indium (156 6 "C,28 44 J g-') and tin (232 1 "C, 60 5 J g-') Table 1 Elemental analytical data (calculated values in parentheses) and yields of the ligands molecular ligand formula C(%) H(%) N(%) yield (YO) 1A 2A 3A 4A 5A 6A 1B 2B 3B 4B 5B 6B 1c 2c 3c 4c5c 6C 68.9 (68.7) 72.1 (72.4) 65.8 (65.8) 74.6 (74.5) 74.2 (74.5) 75.3 (75.0) 69.3 (68.9) 71.9 (71.6) 66.9 (66.8) 73.5 (73.3) 73.4 (73.3) 74.0 (73.7) 70.7 (70.7) 73.1 (73.2) 69.1 (68.8) 75.1 (74.7) 74.7 (74.7) 75.3 (75.0) 6.5 (6.3) 4.3 (4.2) 7.2 (7.0) 4.6 (4.4) 6.2 (6.0) 3.7 (3.8) 7.0 (6.8) 8.6 (8.7) 6.9 (6.8) 8.7 (8.7) 6.9 (7.1) 8.1 (8.3) 5.8 (5.5) 2.9 (3.1) 6.3 (6.0) 2.7 (2.9) 5.7 (5.4) 2.7 (2.9) 6.2 (5.8) 6.1 (6.3) 6.2 (5.8) 6.3 (6.3) 6.5 (6.1) 6.0 (6.1) 6.7 (6.5) 2.8 (2.8) 7.1 (6.9) 2.8 (2.8) 6.7 (6.3) 2.5 (2.6) 7.2 (6.8) 5.7 (5.6) 7.0 (6.8) 5.4 (5.6) 7.2 (7.0) 5.4 (5.5) 64 61 80 71 72 95 70 73 70 69 72 77 91 88 91 89 89 94 Table 2 Elemental analytical data (calculated values in parentheses) and yields of the copper(n) complexes molecular yield complex formula C(Yo) H(%) N(Yo) (Yo) 1A-Cu 62.9 (62.7) 5.7 (5.5) 3.9 (3.9) 38 2A-c~ 65.6 (65.9) 6.4 (6.1) 4.0 (4.1) 40 3A-c~ 65.5 (65.9) 5.4 (5.3) 3.5 (3.5) 50 4A-c~ 67.7 (68.0) 6.3 (6.0) 7.9 (7.7) 67 5A-c~ 67.6 (68.0) 6.2 (6.0) 7.8 (7.9) 73 6A-c~ 68.4 (68.7) 6.7 (6.3) 7.4 (7.6) 61 1B-Cu 66.6 (67.0) 5.1 (5.0) 2.7 (2.9) 38 2B-c~ 66.8 (66.8) 5.6 (5.4) 2.9 (3.0) 78 3B-c~ 62.6 (62.8) 5.0 (4.9) 2.9 (2.7) 47 4B-c~ 68.9 (68.5) 5.6 (5.3) 5.8 (5.8) 78 SB-CU 68.7 (68.5) 5.6 (5.3) 6.0 (5.9) 62 6B-c~ 68.9 (69.0) 6.0 (5.6) 5.4 (5.8) 30 1c-cu 67.0 (66.7) 6.2 (5.9) 2.4 (2.6) 64 2c-cu 68.9 (68.9) 6.3 (6.3) 2.6 (2.7) 54 3c-cu 65.4 (65.1) 6.0 (5.8) 2.2 (2.5) 49 4c-cu 70.1 (70.4) 6.2 (6.2) 4.9 (5.3) 40 5c-cu 70.1 (70.3) 6.3 (6.2) 5.1 (5.3) 59 6C-CU 70.6 (70.8) 6.9 (6.5) 4.9 (5.2) 53 Table 3 Elemental analytical data (calculated values in parentheses) and yields of the oxovanadium(rv) complexes molecular yield complex formula C(Yo) H(%) N(%) (Yo) 1B-VO C26H24F2N05V 63.9 (64.3) 5.7 (5.5) 2.7 (2.9) 35 2B-VO C26H25FNOsV 67.0 (66.6) 5.7 (5.3) 2.9 (3.0) 52 3B-VO C2,H2,F3N05V 62.9 (62.6) 5.0 (4.8) 2.7 (2.7) 50 4B-VO C2,H2,N20SV 68.7 (68.3) 5.7 (5.3) 5.5 (5.9) 65 5B-VO C27H25N,05V 68.1 (68.3) 5.4 (5.3) 5.8 (5.9) 30 6B-VO C28H27N205V 69.2 (68.8) 5.7 (5.5) 5.8 (5.7) 351c-vo C3,H32F2N05V 66.9 (66.5) 6.0 (5.9) 2.4 (2.6) 53 2c-vo C30H33FN05V 68.7 (68.6) 6.7 (6.3) 2.3 (2.7) 73 3C-VO C31H33F3NOSV 65.1 (64.9) 6.1 (5.8) 2.2 (2.4) 35 4C-VO C31H33N205V 70.3 (70.1) 6.0 (6.2) 5.1 (5.3) 45 5C-VO C31H33N20SV 69.9 (70.1) 6.0 (6.2) 5.1 (5.3) 25 6C-VO C32H35N205V 70.3 (70.5) 6.8 (6.4) 5.2 (5.1) 60 Results and Discussion Synthesis and characterization Ligands.The ligands of series A, B and C were synthesized by condensation in warm ethanol using the appropriate aniline with the aldehyde obtained by alkylation of 2,4-dihydroxy- benzaldehyde (series A) and by esterification of 2,4-dihydroxy- benzaldehyde with the acid-chloride derivative of 4-decyloxybenzoic acid (series B and C).The C=N stretching vibration in the ligands is located in the 1619-1630 cm-' (series A) and 1613-1625 an-' (series B and C) range. Compounds in series B and C also show a stretching band between 1718 and 1740 cm-', assigned to the ester group v (C=O). The CN stretching band is located in the 2246-2251 cm-I range for ligands with the group CH,CN, 2228-2232 cm-' for ligands with the CN group in position 3 and 2220-2223 cm-I for ligands with the CN group in position 4.As can be observed, there is a shift to lower frequencies: 4-CH2CN>3-CN >4-CN due to increasing conjugation. Complexes. The copper(r1) complexes were prepared by reacting the appropriate imine with copper(I1) acetate mono- hydrate in warm ethanol. The oxovanadium complexes were prepared by reacting the appropriate imine with vanadyl sulfate pentahydrate and triethylamine in warm methanol. The complexes are soluble in toluene, chloroform, dichloro- methane and insoluble in hexane, diethyl ether and ethanol. Elemental analyses of the complexes were consistent with their proposed structures (Tables 2 and 3). The C=N stretching vibration is shifted to lower frequencies for the complexes (copper, 1611-1620 cm-'; oxovanadium, 1607-1620 cm-') compared to that of the free ligands (1613-1632 cm-I).This indicates that the azomethine N atom is involved in metal- nitrogen bond formation. The oxovanadium complexes also exhibit a stretching band at around 983-987 cm-' assigned to v (V-0); this suggests that these complexes have a monomeric structure." Mesogenic behaviour The optical, thermal and thermodynamic data of the ligands and the complexes are summarized in Tables 4 and 5, respect-ively, and Fig. 1-7 represent the mesophase ranges for the ligands and complexes. Mesogenic properties of the ligands. As can be observed in Table 4 and Fig. 1-3, among the ligands of series A only the compound with the CN group in position 4 (X=Y=H, Z= CN) exhibits mesomorphism.The absence of mesomorphism in most of the ligands in series A can be accounted for by the low molecular length :width ratio. However, the presence of the CN group in position 4 makes nematic mesomorphism possible, probably due to the increase in electronic polariz- ability along the molecular axis. On the other hand, all the compounds of series B and C exhibit liquid-crystal properties The type of mesophase is influenced by the length of the alkoxybenzoyloxy group and by the polar group. Thus, the 150 100 9R RN oc 50 0 1A 2A 3A 4A 5A cornDound Fig. 1 Transition temperatures for the ligands of series A J. Muter. Chem., 1996,6(3), 349-355 351 Table 4 Optical, thermal and thermodynamic data for the ligands ligand X Y Z transition T/"C AHlkJ mol 1A F H F c-I 74 0 33 5 2A H F H c-I 55 2 35 3 3A H CF3 H c-I 48 8 28 8 4A H CN H c-I 69 2 29 0 5A H H CN C-N 83 5 40 5 N-I 125 3 14 6A H H CH2CN c-I 100 4 25 8 1B F H F C-N 96 7 23 24 N-I 214 5 191 2B H F H C-N 90 5 26 7 N-I 155 8 0 71 3B H CF3 H c-I 99 6 I-N" 87 6 N-Sc" 70 6 4B H CN H c-I 127 0 33 9 I-N" 120 9 0 38 5B H H CN C-SA 104 1 34 24 SA-N 127 Xb N-I 248 9' 6B H H CH,CN C-N 140 6 37 2 N-I 234 6 06 1c F H F C-N 86 5 33 2 N-I 184 2 16 2c H F H c1-c2 59 4 54 C2-N 80 7 23 9 N-I 127 7 09 N-Sc" 81 9 04 3c H CF3 H c-I 97 9 37 8 I-SA" 80 3 21 4c H CN H c-I 123 3 25 4 I-N" 115 4 09 5c H H CN C-SA 106 8 42 7 SA-I 240 4b 6C H H CHZCN C-SA 136 9 40 7 SA-N 191 3 02 N-I 213 7 11 SA-SC" 136b " Monotropic transition Optical data 200 200 EdN EZIN0P SA SA fJ sc fJ sc 100 oc 100 oc n 0 18 20 38 38' 48 48' 58 68 1C 2C 2C' 3C 3C' 4C 4C' 5C 6C 6C' corn pou nd cornpound Fig.2 Transition temperatures for the ligands of series B Fig. 3 Transition temperatures for the ligands of series C fluoro derivatives [2,4-difluoro (X=Z =F, Y =H) or 3-flU01-0 those of series A due to the presence of an aromatic ring joined (X=Z=H, Y=F)] exhibit a nematic phase in both series B by an ester bond to the structure derived from 2-hydroxy- and C, whereas the 4-cyano denvatives exhibit a nematic benzylideneaniline This involves important structural changes, mesophase in ligands of series B and mainly a smectic A phase in particular an increase in the molecular length with little or in ligands of series C Both derivatives 3-CF3 (X=Z=H, Y= no change in the width, and an extension of the conjugation CF3) and 3-CN (X =Z =H, Y =CN) in series B exhibit mono- through the ester bond (which means an increase of the tropic mesomorphism The 3-CF3 denvatives exhibit nematic electronic polarizability of the molecule) These two factors and smectic C mesophases, whereas the 3-CN derivatives only allow an increase in the anisotropy of the polarizability for show nematic mesomorphism molecules with three aromatic rings, which favours molecular The absence of enantiotropic mesomorphism in these com- interactions and liquid-crystal properties for the ligands in pounds can be explained by the steric hindrance of a big group series B and C such as CF, or CN in position 3, which is unfavourable for By comparing the melting temperatures of the ligands of mesophase stability Ligands of series B and C are different to series A, B and C, the following sequencies can be established 352 J Muter Chem , 1996,6(3),349-355 series A: 4-CN >4-CH2CN>2,4-diF >3-CN >3-F >3-CF3 series B: 4-CN >4-CH2CN>2,4-diF >3-F >3-CN >3-CF, series C: 4-CN >4-CH2CN>2,4-diF >3-F >3-CN >3-CF3 As can be seen, in each of the three series the nature of the group and its position have a similar influence on the melting temperature.However, the effect of the group on the appear- ance of mesomorphism and on the type of mesophases formed is very different for the three series.Mesogenic properties of the copper(1r) complexes. The com- plexes of series A-Cu are not liquid crystalline, with the exception of the complex with two fluoro atoms in positions 2 and 4 (X=Z=F, Y=H) which exhibits a smectic A meso- phase (Table 5, Fig. 4). The complexes of series B-Cu and C- Cu exhibit smectic A and nematic phases (Table 5, Fig. 5 and 6). The nematic phase of the complexes shows textures that are typical of this type of mesophase, the marbled texture on heating and the schlieren texture on cooling. The smectic A phase of the complexes was identified by the appearance on heating of both the mielinic and homeotropic texture. Homeo tropic and focal-conic textures were observed on cooling from the isotropic liquid.The type of mesophase formed is affected by the polar group and by the length of the 4-alkoxybenzoyloxy group in series B-Cu and C-Cu. It is observed that the CN group gives rise to a smectic A mesophase in both series B-Cu and C-Cu, with the exception of the 4-CN derivative with n =6 (series B-Cu) which exhibits a nematic mesophase. The complexes with fluorine atoms in the structure (2,4-diF, 3-F and 3-CF3) exhibit nematic meso- morphism in both series. This phase is monotropic for n=6 with a CF, group due to the volume of this group in position 3 which destabilizes the mesophase. The highest melting temperatures are exhibited by the 4-CN 300-SA oc16A-CU 1A-c~ PA-CU 4A-c~ 5A-CU compound Fig.4 Transition temperatures for the complexes of series A-Cu 300-I BN SA oc " 16-Cu 26-CU 3B-CU 36-CU' 4B-c~ 58-CU 6ECu compound Fig. 5 Transition temperatures for the complexes of series B-Cu 3001 200 ON9F H SA oc 100 IC-Cu 2C-CU 3C-CU 4C-CU 5C-CU 6C-CU compound Fig. 6 Transition temperatures for the complexes of series C-Cu derivatives. The mesomorphic stability of these complexes is due to the fact that the substituent is parallel to the main axis of the molecule and gives rise to less steric hindrance and higher anisotropy of polarizability, thus favouring intermolecu- lar interactions. A comparative study of the melting temperatures allows us to establish the following sequences: series A-Cu: 4-CN >4-CH2CN>2,4-diF >3-CF, >3-CN >3-F series B-Cu: 4-CN >3-F >4-CH2CN>2,4-diF >3-CN >3-CF3 Series C-Cu: 4-CH2CN>3-CN >2,4-diF >3-F >3-CN >3-CF3 In contrast to the uncomplexed ligands, in these complexes the groups and their position have a different influence on the mesomorphism in series A-Cu, B-Cu and C-Cu.The steric effect of the lateral groups decreases the stability of the mesophase, and the sequences of clearing temperatures for the complexes of series B-Cu and C-Cu are: series B-Cu: 4-CN >2,4-diF >3-F >3-CN >4-CH2CN>3-CF, series C-Cu: 4-CN >2,4-diF >4-CH2CN>3-CN >3-F >3-CF3 The negative influence of the lateral substituents is similar to that observed for the ligands, but less marked.Such a lateral- group effect has also been observed by another research group." Mesogenic properties of the oxovanadium (rv) complexes. As can be observed in Table 5 and Fig. 7 and 8, mesogenic behaviour is not favoured for these complexes, in contrast to their ligands and to the homologous copper(I1) complexes. Only three complexes in series B-VO (2,4-diF, 3-F and 4- CH,CN) and four complexes in series C-VO (2,4-diF, 3-F, 4-CN, 4-CH2CN) exhibit liquid-crystal properties. The fluoro derivatives (2,4-diF, 3-F) exhibit a nematic mesophase, but the 3-F derivative exhibits a monotropic mesophase in both series. The absence of enantiotropic meso- morphism in these compounds is probably due to the greater steric hindrance of the VO group compared with the Cu group.In general, the melting and clearing temperatures are higher for the complexes of series B-VO than for the complexes of series C-VO, as was also seen for the copper(I1) complexes. The sequence for the melting temperatures is: series B-VO: 3-CN >3-F >4-CH2CN>4-CN >3-CF3>2,4-diF series C-VO: 3-F >4-CN >3-CN >3-CF3>2,4-diF >4-CH2CN The effect of the volume of the VO group has a greater J. Mater. Chem., 1996, 6(3), 349-355 353 Table 5 Optical, thermal and thermodynamic data for copper@) and oxovanadium(1v) complexes complex X Y Z transition T/"C AH/kJ mol-' 1A-CU F H F C-SAs*-I 136.9 150.3 45.2 4.2 2A-c~ H F H c1-c2 100.4 5.8 c2-I 167.6 50.1 3A-c~ 4A-c~ H H CF3 CN H H c-I c-I 124.9 122.6 37.4 57.3 5A-c~ H H CN c-I 201.4 41.0 6A-c~ H H CH2CN c-I 180.1 57.8 1B-Cu F H F c1-c2 193.8 38.1 C2-N 204.5 22.0 N-I 279.5 1.3 2B-c~ H F H C-N 218.1 39.0 N-I 230.5 2.0 3B-c~ H CF3 H c-I I-N" 174.8 146.0' 58.6 4B-c~ H CN H C,-C2C2-N 203.9 21 1.4 2.1 43.8 N-I 230.4 1.6 5B-c~ H H CN C-SA 252.2 61.9 SA-I 286.5' 6B-c~ H H CH2CN CrC2 170.2 29.1 c2-sA 205.2 41.2 SA-N 227.0 N-I 230' 1.1 1c-cu F H F c1-c2 161.7 59.3 C2-N 170.8 54.2 N-I 265.3 1.48 2c-cu H F H C1-C2 C2-( N +C) (N+C)-NN-I 80.7 166.3 171.9 195.5 12.0 57.2 6.2 1.6 3c-cu H CF3 H c1-c2 58.5 28.0 C2-N 146.7 46.7 N-I 150.1 1.5 4c-cu H CN H C-SAs*-I 165.1 205.7 43.5 5.0 5c-cu H H CN c1-c2 176.1b c2-c3 186.0 65.20 C3-SA 193.5 17.1 SA-I 276'9' 6C-CU H H CHzCN C-SA 199.8 66.6 SA-I 231.4' 1B-VO F H F C-N 21 1 30.4 N-I 249.4 0.9 2B-VO H F H c,-c2c2-I 222.7 246.7 1.55 50.4 I-N" 190' 3B-VO 4B-VO H H CF3 CN H H c-I c-I 182.9 249.3 62.2 76.1 5B-VO H H CN c-I 195.8 90.2 6B-VO H H CH2CN c1-c2 131.3 6.02 1c-vo F H F c24, c42 SA-I 245 286.2b*' 58.8 43.2 14.9 C2-N 144.6 41.4 N-I 198.1 0.5 2c-vo H F H c-I 217.3 60.7 I-N 174.5 0.6 3C-VO 4C-VO 5C-VO H H H CF3 CN H H H CN c-I C-Sc,, Sclys-1c-I 181.7 188.5 21@ 203.9',' 76.4 10.1 34.1 6C-VO H H CH2CN C-Sc*ys SclY*-I 141.0 231.9 22.6 31.7 ~~~~ ~ Monotropic transition.Microscopy data. 'Complex partially decomposed. influence than the volume effect of the polar groups on the C,-C,-mesophase or isotropic liquid transitions while, com- appearance of liquid-crystal properties. Complexes 3-CN and plex SC-Cu (4-CN) exhibits a C1-C,-C,-mesophase transition 4-CH2CN of series C-VO exhibit a smectic crystal phase. sequence. Crystalline polymorphism. It is observed that most of the Conc,usionscomplexes exhibit crystalline polymorphism. This is typical for mesogenic compounds. Complexes 2A-Cu, 1B-Cu, 4B-Cu, The 4-alkoxybenzoyloxy group favours the appearance of 6B-Cu, 2B-VO, 6B-VO, 1C-Cu, 3C-Cu7 1C-VO exhibit mesogenic properties with respect to the 4-alkoxy group.The 354 J. Muter. Chem., 1996,6( 3), 349-355 200 0 BNk SA oc 100 0 1B-VO 28-VO 28-VO' 36-VO 4B-VO 58-VO 68-VO compound Fig. 7 Transition temperatures for the complexes of series B-VO 200 g 100 n.. IC-VO 2C-VO 2C-VO' 3C-VO 4C-VO 5C-VO 6C-VO cornpound Fig. 8 Transition temperatures for the complexes of series C-VO complexes with the cyano group yield mainly a smectic A mesophase whereas the corresponding ligands, in addition to a smectic A phase, also exhibit a nematic phase. The presence of a fluorine atom favours the nematic mesophase in both ligands and complexes.The mesophase ranges are wider in the ligands than in the complexes, which might be explained by the greater volume and the lower length: width ratio of the complexes, which decrease the stability of the mesophase. The copper(1r) com- plexes exhibit better mesogenic behaviour than the analogous oxovanadium(1v) complexes, which may be explained on the basis of geometric factors: copper(I1) complexes have a square- planar coordination, whereas the oxovanadium(1v) complexes have a square-pyramidal coordination. It is observed that for the copper@) complexes the polar group has a large influence on the transition temperatures owing to the square-planar geometry of these complexes around the metal centre, whereas in oxovanadium(1v) complexes it is the VO group that has the greater influence, with the polar groups playing a secondary role.This work was supported by the CICYT (Spain), project nos. MAT93-0104 and MAT94-07 17-CO2-01. References 1 A. M. Giroud-Godquin and P. M. Maitlis, Angew. Chem., Znt. Ed. Engl., 1991, 30, 375; P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and E. Sola, Coord. Chem. Rev., 1992, 117, 215; D. W. Bruce, in Inorganic Materials, ed. D. Bruce and D. O'Hare, Wiley, Chichester, 1992; S. A. Hudson and P. M. Maitlis, Chem. Rev., 1993,93, 861; D. Bruce, J. Chem. SOC., Dalton Trans., 1993,2983. 2 R. H. Holm and M. J. O'Connor, Prog. Znorg. Chem., 1971,14,477. 3 I. V. Ovchinnikov, Yu. G. Galyametdinov, G. I. Ivanova and L. M.Yagfarova, Dokl. Akad. 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