J. MATER. CHEM., 1991, 1(1), 29-35 Synthesis, Structure, and Spectroscopic and Electrochromic Properties of Bis(phthalocyaninato)zirconium(w)t Jack Silver,*" Peter Lukes," Stuart D. Howea and Brendan Howlinb a Department of Chemistry and Biological Chemistry, University of Essex, Wivenhoe Park, Colchester C04 3SQ, UK Department of Chemistry, University of Surrey, Guildford GU2 5XH, UK The crystal structure of the title Fompound [Zr(pc),] has been solved by X-ray diffraction techniques. The cell is triclinic, Pi; a= 13.410(2) A, b= 13.400(7) A, c= 16.340(11) A, a=68.68(1)", fi=65.92(1)", y=74.74(1)", R=0.039 and R'=0.058 for 6576 reflections. The infrared spectrum and details of the solvent dependence of the electronic absorption spectrum are also given. [Zr(pc),] has the most distorted rings of all the metal bisphthalocyanines so far reported.The distortion is primarily caused by the Zr-N distances (average 2.30 A), which though long for such Zr bonding, are very small when compared to other M-N bonds in similar structures. Cyclic voltammograms of [Zr(pc)J are presented and discussed. The distorted structure has a detrimental effect on the electrochromic properties of the molecule, aiding decomposition during oxidation. Keywords: Bisphthalocyanine; Zirconium; Crystal structure; Cyclic voltammetry Since their discovery by Kirin, Moskalev and co-workers,' the bis(phthalocyaninato)lanthanide(rn)complexes have gener- ated a great deal of interest. Their electrochromic properties are the main driving force for the sustained interest, and several different groups of workers have systematically explored these compounds.' -6 Electrochromism is the term describing the phenomenon of an electrochemically induced colour change in a material.We and others have achieved better than lo7 colour cycles in bis(phthalocyaninato)lanthanide(IrI) device^.'^.^ From the many papers on these materials that have appeared,'-' the present consensus of opinion is that the neutral green parent material can be formally written as [M(pc)(p~*)]~ (where pc= the phthalocyaninato 2- anion, and pc. is the phthalocyanin- ato 1-mono radical anion); the red oxidised form contains two radicals [M(pc.),]+ and the blue mono reduced species is [M(pc),]-. There is also a further reduced purple [M(pc),12- species though the exact nature of this is not yet clear.Several structures of metallo-bisphthalocyanine complexes have been characterised by X-ray diffraction studies. Main block,8 lanthanide'-' ' and actinide' 2,1303b metals have been found in such structures. There have been suggestions that the heavier transition metals may also form such complexes, but to date no such compounds have been fully character- ised.14 The known structures of all the metal bisphthalocyan- ines show the same type of non-perfect square antiprism geometry around the metal centre. However, there are some subtle differences both in the planarity of the phthalocyanine rings [they can both be dianion (pc), or one can be a dianion and the other a monoanion radical (pc.)] and in the fact that the metals may be either tri- or tetra-valent.In our e~perience'~ the Sn" material did not display all the colours derived in the lanthanide(r1r) materials,' though others have suggested that it does.5 Because of this, we investigated the electrochromic properties of bis(phtha1ocyani-nato)zirconium(rv) and, as for the Sn" compound, found t Supplementary data available from the Cambridge Crystallo- graphic Data Centre: see Information for Authors, J. Muter. Chem., 1991, Issue 1. only limited colour changes available; on oxidation the materials lost its colour.' We therefore undertook a structural investigation of bis(phthalocyaninato)zirconium(Iv) which is reported here along with spectroscopic studies and cyclic voltammetry on this material.We discuss the structure in relation to other similar structures and also in relation to its electrochromic properties. Experimenta1 We have reported the synthesis of bis(phtha1ocyaninato) zirconium(rv), [Zr(pc),], e1se~here.I~Crystals suitable for X-ray diffraction were grown in a tube furnace from crude material by passing the material several times through the furnace with a slow flow of nitrogen. We wish to add a cautionary note here, if one attempts to prepare [Zr(pc),] from zirconium acetate rather than ZrC1, as in the reaction of [LU(~C)~CH&~~],'~ then a Zr material which has an electronic spectrum similar to [Lu(pc)(OAc)( H ,O),] H,0.2CH ,C1, is always present as a major contaminant.This is difficult to remove. We believe this material probably contains [(pc)Zr(OAc),] but did not pursue it further. Its solution spectrum in CH2Cl, contains two equally intense peaks at 627 and 658 nm. X-Ray Structural Investigation Crystal Data: C64N16H32Zr,M = 1124.36, triclinic, a = 13.410(2)A, b= 13.400(7)A, c= 16.340(11)A, a=68.68(1)",fi= 65.92( ly, y =74.74( l)', V= 2474.4 A3 (by least-squares refine- ment of 25 automatically centred reflexions, ;L =0.71069 &), space group Pi,Z =2, D, =2.509 g cm -'. Approximate crystal dimensions 0.2 mm x 0.2 mm x 0.1 mm, F(000)= 1152, p(Mo-Ka)=2.78 1 cm -'. Data Collection and Processing:' Enraf-Nonius CAD4 diffractometer, omega/2@ mode with omega scan width = 0.80+0.35 tan@, omega scan speed 3.33 min-', graphite-monchromated Mo-Ka radiation; 8 124 unique reflexions mea- sured (1 <@/" <24) yielding 6576 with I >2.58a(I). Structure Analysis and Rejnement: Direct methods and Pat- terson (Zr atom) followed by normal heavy-atom methods.Full-matrix least-squares refinement with all non-hydrogen atoms anisotropic and hydrogens in calculated positions. The weighting scheme w =Lp/[a2(I) +(0.6 Z)2]* where I =raw intensity, gave satisfactory agreement analyses. No reflexions were omitted because of extinction. Final R and R’ values were 0.039 and 0.058, respectively. Programs and computers used and sources of scattering factor data are given in ref. (16). Atomic co-ordinates are given in Table 1.Cyclic Voltammetry An EG & G applied research model potentiostat, connected to a Philips PM8271 XYT recorder, was used to record cyclic voltammograms of thin films of [Zr(pc),]. The working electrode was a gold film deposited onto a glass slide which had previously been coated with a thin layer of chromium metal. All [Zr(pc),] films were deposited under vacuum (10- Torrt). Other working electrodes were indium- doped tin oxide (ITO) covered glass on which the [Zr(pc),] was sublimed. The counter electrode was a 1 cm2 Pt gauze, and a silver wire constituted the pseudo-reference electrode. The voltammetry was recorded in deionised water using 5% KC1 as the supporting electrolyte. Prior to recording the voltammetric data the solution was degassed, and an N2 atmosphere was maintained throughout the experiment.Infrared Spectroscopy The infrared spectrum of [Zr(pc)J was collected on material sublimed from single crystals directly onto KBr plates. It was also collected on a Perkin-Elmer 17 10 Fourier Transform infrared spectrometer from single crystals ground with KBr and pressed as a disc. Both spectra agreed with each other in band positions and intensities (see Table 2). Table 2 also contains the data for the [Sn(pc),] p-phase” which is very similar to the data of [Zr(pc),]. UV-VIS Spectroscopy We have previously shown the electrochromic absorption spectra of a thin film of [Zr(pc),] sublimed on indium-doped tin oxide covered glass (ITO) recorded by a Perkin-Elmer Lambda 5 spectrophotometer.15 Two Q bands are apparent at 702 and 637nm in the spectrum of the neutral complex, which may indicate the presence of two phases; however, no evidence for two phases was apparent in the infrared data discussed above.Also, on oxidation of the film both Q bands disappear together, suggesting that if more than one sublimed phase is present their electrochromic behaviour is similar. A better explanation of the appearance of the two bands in the Q region is that they arise from different vibrational com-ponents of the same transition.I8 This implies that the [Zr(p~)~]molecule is asymmetric about the xy plane. This finding is borne out by the crystallographic data. The electronic absorption spectrum of [Zr(pc),] shows solvent dependence; in chloronaphthalene bands are observed at 687.0 nm and a shoulder at 635 nm (relative intensities 4:l); in dimethylformamide bands shift to 678.0 and 613 nm (rel. int.4:1), in CH2Cl, the bands are at 684 and 618 nm (rel. int. 5:1). t 1 Torr ~133.322Pa. J. MATER. CHEM., 1991, VOL. 1 Table 1 Table of positional parameters and their estimated standard deviations“ atom X Y Z Bj A’ Zr 0.52206(2) 0.2045 3( 2) 0.74244( 2) 2.83 1 (6) N1A 0.6955( 2) 0.2400(2) 0.7 109( 2) 3.24(5) CIA 0.72 13(2) 0.3329(2) 0.7098( 2) 3.62(7) C7A 0.881 6( 2) 0.2518(3) 0.6261(2) 3.87(7) C8A 0.7931(2) 0.1873(2) 0.6632(2) 3.47(7) N2A 0.812I(2) 0.0889(2) 0.6559(2) 3.64(6) C9A 0.7390(2) 0.0214(2) 0.7077( 2) 3.32(7) ClOA 0.7679( 2) -0.0926(2) 0.7 145(2) 3.62(7) C11A 0.8610(3) -0.1509( 3) 0.665 l(2) 4.73(9) C12A 0.8620(3) -0.2608(3) 0.69 15(3) 5.7(I) C13A 0.7769( 3) -0.3114(3) 0.7645( 3) 5.6( 1) C14A 0.6858(3) -0.2533(2) 0.8136(2) 4.51(8) C15A 0.681 l(2) -0.1425(2) 0.7861(2) 3.5q7) C16A 0.5985(2) -0.0574(2) 0.8194(2) 3.19( 6) N3A 0.63 3 3( 2) 0.041 l(2) 0.7682(1) 3.15(5) N4A 0.5047( 2) -0.0783(2) 0.8902( 2) 3.32(5) C17A 0.4337(2) -0.0019( 2) 0.9250(2) 3.19(6) C18A 0.3343(2) -0.0260(2) 1.0053(2) 3.42( 6) C19A 0.2872(3) -0.121 8(3) 1.0547( 2) 4.26(8) C20A 0.1852(3) -0.1 145(3) I.1242(2) 4.8 2(9) C21A 0.1334(3) -0.0175(3) 1.145 l(2) 5.1(1) C22A 0.18 1 l(3) 0.0757( 3) 1.0980(2) 4.32(8) C23A 0.2830(3) 0.0700(2) 1.0263(2) 3.44( 7) C24A 0.3525(2) 0.1507(2) 0.9602(2) 3.24( 6) N5A 0.4399( 2) 0.1069( 2) 0.8956( 1) 3.08(5) N6A 0.3 343( 2) 0.2499(2) 0.9660(2) 3.41(5) C25A 0.4067( 2) 0.3191(2) 0.91 16(2) 3.3 3( 6) C26A 0.3960(2) 0.4201(2) 0.9288(2) 3.73(7) C27A 0.3159(3) 0.47 15(3) 0.993 1 (2) 4.41(8) C28A 0.3 350(3) 0.5688(3) 0.99 14(2) 5.14(9) C29A 0.4279(3) 0.61 37(3) 0.9292( 2) 5.30(9) C31A 0.4906( 2) 0.4659(2) 0.866 1(2) 3.70( 7) N7A 0.5007(2) 0.3056(2) 0.8376( 1) 3.16(5) N8A 0.6563( 2) 0.4062( 2) 0.7525(2) 3.73( 6) C32A 0.5560( 2) 0.39 15(2) 0.8 1 18(2) 3.42(6) C30A 0.5072(3) 0.564 1 (3) 0.8652(2) 4.65(8) C6A 0.9933(3) 0.234 l(3) 0.5728(3) 5.09(9) C5A 1.0564( 3) 0.3113(4) 0.5543(3) 6.3( 1) C4A 1.0125( 3) 0.4004(3) 0.5877( 3) 64 1) C3A 0.9025(3) 0.4 185(3) 0.6396(3) 5.7( 1) C2A 0.8366( 2) 0.34 1 7( 3) 0.6567(2) 4.19(8) N7B 0.421 l(2) 0.0995( 2) 0.7299( 1) 3.3 l(5) C1 B 0.2483(2) 0.2482( 3) 0.81 39( 2) 4.1 l(7) NIB 0.3440(2) 0.29 36( 2) 0.76 56( 2) 3.39(5) N5B 0.608 l(2) 0.1776(2) 0.5965(1) 3.28(5) C24B 0.6200(2) 0.0823(2) 0.5772(2) 3.57(7) C16B 0.6226(2) 0.3993(2) 0.5556( 2) 3.44(6) C8B 0.3 122(2) 0.4026(3) 0.7595(2) 3.86(7) N2B 0.3715(2) 0.48 19(2) 0.71 12(2) 3.90(6) C9B 0.4716(2) 0.4673(2) 0.6505(2) 3.46(6) N3B 0.5321(2) 0.37 17(2) 0.6339(2) 3.26(5) C15B 0.6245(2) 0.5154(2) 0.5250(2) 3.89( 7) C14B 0.6992( 3) 0.58 12( 3) 0.45 12( 2) 4.68(8) C13B 0.6743(3) 0.6906( 3) 0.4426( 2) 5.42(9) C12B 0.5 804( 3) 0.7331(3) 0.5025(2) 5.43( 9) CllB 0.5043( 3) 0.6686(3) 0.5750(2) 4.8 5(8) ClOB 0.5296( 2) 0.557 1( 2) 0.5857( 2) 3.85(7) N4B 0.6965( 2) 0.3 372( 2) 0.5056(2) 3.6 3( 6) C17B 0.6852(2) 0.2364(2) 0.5229( 2) 3.62( 7) C18B 0.753 3( 2) 0.1746(3) 0.4580(2) 3.99(7) C19B 0.8438(3) 0.197 l(3) 0.3752( 2) 5.1( 1) C20B 0.8890(3) 0.1193( 3) 0.3298(3) 5.9( 1) C21B 0.8469( 3) 0.0234( 3) 0.3618(3) 5.8( 1) C22B 0.7577(3) O.O006( 3) 0.4436(2) 5.07(9) C23B 0.7117(2) 0.0783(3) 0.49 13(2) 4.01(8) N6B 0.5581(2) 0.0040(2) 0.623 3( 2) 3.79(6) C25B 0.4651(2) 0.01 39( 2) 0.692 7( 2) 3.56( 6) C32B 0.3 145(2) 0.0826(2) 0.78 8 1 (2) 3.60(7) N8B 0.2348(2) 0.1486(2) 0.8294(2) 4.34(7) C31B 0.2944(2) -0.02 15( 3) 0.7699( 2) 4.23(7) C26B 0.3889(2) -0.0650(2) 0.7366(2) 4.05(7) C27B 0.3973(3) -0.1660(3) 0.7266(2) 5.41(9) C28B 0.3095(3) -0.2223(3) 0.7801(3) 641)C29B 0.2153(3) -0.1807(3) 0.84 13(2) 6.3( 1) J.MATER. CHEM., 1991, VOL. 1 Table 1 (continued) atom Y Y z B/A' C30B 0.2044(3) -0.0791(3) 0.8514(2) 5.40(9) C2B 0.1574(3) 0.3270(3) 0.8455(3) 5.16(9) C7B 0.1963( 3) 0.4231(3) 0.81 19(2) 4.97(9) C6B 0.1275(3) 0.5172(4) 0.8291(2) 7.q1)C5B 0.0192(4) 0.5093(4) 0.8829(5) 9.6(2)C4B -0.0209(4) 0.41 12(4) 0.9170(5) 10.4(2) C3B 0.0444(4) 0.3176(4) 0.9007(4) 7.7(2) a Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as 3[2aB( 1,l) + 2b B(2,2)+ 2cB(3,3)+ abB(1,2)cosy+ acB(1,3)cosP+ bcB(2,3)cosa] Table 2 Absorption frequencies mp4, P-Sn(Pch" relative relative frequency/cm-intensity frequency/cm-intensity 485 483 506 504 567 565 629 625 -640' 731 725 746 742 778 772 -796 815 811 8 70 866 894 890 950 946 1003 1002 1038 1041 -1059 1074 1075 1118 1119 1162 1166 -1209 1287 1287 -1321 1333 1335 1384 1383 1421 1425 -1450 1467 1477 1505 1508 1595 1550 1609 1613 Data from ref.(17). Relative intensities were not given but are estimated from Fig. 1 of that text. ' Not seen in Fig. 1 of ref. (17), but it is recorded in the text table. Results The structure of [Zr(pc),] is shown in Fig. 1, the bond lengths are given in Table 3 and the angles around the Zr atom in Table 4.To appreciate the structure it is best to first consider the deviations of the atoms from the mean pyrrole N, plane in the pc rings.It is apparent that these rings are very distorted and the overall structure resembles two back-to-back exagger- ated saucers. Table 5 gives a comparison of the distortions of the rings in this structure and those in some of the other known structures. Table 6 presents other major comparisons of the structures. As the Zr structure is the most distorted to date, we will refer to it henceforth as the 'wok-wok' structure. The Zr-N distances vary from 2.293(2) to 2.315(2) 8, with a mean distance of 2.30 A. This is smaller than those of the other known structures and presumably reflects the fact that Zr" is the smallest cation in eight co-ordination in the bis(phtha1ocyaninato) metal structures so far elucidated. This Fig.1 Structure of [Zr(pc),] with the numbering scheme used for the atoms in the molecule. The rings are indicated by the letters immedi- ately to their side is surprising in view of the conventionally quoted radii for Sn" and Zr"" and suggests that these do not hold for N-ligand co-ordination. The effect of the small Zr-N distances is that the pc rings are drawn in towards the Zr" cations, and the mean pyrrole N4 to pyrrole N4 plane distances (Table 7) are smallest in this structure.? This is the driving force behind the main buckling of the ring. Even though the two rings are staggered at an angle of 42", this close N4-N4 plane proximity means that the n clouds are interdigitating and add to the distortion of the rest of the pc rings from the N4 planes.In fact, it is only the outer six-membered carbon rings that are as far apart as would be expected for non-interpenetrating n clouds. In contrast, the rings of the other known structures, all of which have larger metals at their centre, are well separated at all atoms other than the inner N4 plane on the macrocycles. The staggering angle of 42" for the Zr" structure is the same as that found in the Sn" structure. For the other structures, the angle depends on the six-membered rings chosen between t We have calculated the mean distance between the N, planes of the two pc rings in [Zr( c),] on a graphics package using COSMIC. It was found to be 2.00 1.If we calculate the centroid of four nitrogen to centroid of four nitrogen distance using a simple geometric model we get a distance of 2.53 A.The centroid distance is larger owing to the uneven tilting of the nitrogens. Both these values compare favourably with the centroid-to-centroid distance of 2.20 A calculated using GEOSTAT. Hence, for the worst estimate the distance between planes is less than that found in the structure, at best it is significantly less than the tin. J. MATER. CHEM., 1991, VOL. 1 Table 3 Bond distanceslk atom 1 atom 2 distance atom 1 atom 2 distance atom 1 atom 2 distance Zr Zr Zr Zr Zr Zr Zr Zr N1A N1A C1A C1A C7A C7A C7A C8A N2A C9A C9A ClOA ClOA C11A C12A C13A C14A C15A C16A C16A N4A C17A C17A C18A C18A C19A C20A N1A N3A N5A N7A N7B N1B N5B N3B C1A C8A N8A C2A C8A C6A C2A N2A C9A ClOA N3A C11A C15A C12A C13A C14A C15A C16A N3A N4A C17A C18A N5A C19A C23A C20A C21A 2.308(3) 2.307(2) 2.305(2) 2.302(3) 2.301(3) 2.315(2) 2.304(2) 2.293(2) 1.369(5) 1.3 79( 3) 1.327(4) 1.444(4) 1.446(5) 1.399(4) 1.369(5) 1.3 15(4) 1.3 1 5( 4) 1.448(4) 1.38 1( 3) 1.393(4) 1.3 79(4) 1.374(5) 1.376(5) 1.3 77( 5) 1.377(4) 1.455(4) 1.365( 3) 1.328(3) 1.32 l(3) 1.447( 3) 1.373(4) 1.398(4) 1.38 l(4) 1.384(4) 1.393(5) C21A C22A C23A C24A C24A N6A C25A C25A C26A C26A C27A C28A C29A C31A C31A N7A N8A C6A C5A C4A C3A N7B N7B C1B C1B C1B N1B N5B N5B C24B C24B C16B C16B C16B C8B C22A C23A C24A N5A N6A C25A C26A N7A C27A C31A C28A C29A C30A C32A C30A C32A C32A C5A C4A C3A C2A C25B C32B N1B N8B C2B C8B C24B C17B C23B N6B N3B C15B N4B N2B 1.37 1( 5) 1.397(4) 1.436(4) 1.383(3) 1.3 19(4) 1.327(4) 1.440(5) 1.37q3) 1.39 5( 4) 1.3 89( 4) 1.38 3( 6) 1.365(5) 1.376(5) 1.449(4) 1.386(5) 1.376(4) 1.3 13( 3) 1.380(7) 1.383( 7) 1.3 76( 5) 1.409(6) 1.375(4) 1.380(3) 1.369(4) 1.3 13(5) 1.440(4) 1.388(4) 1.379(4) 1.365(3) 1.448( 3) 1.3 15(4) 1.368(3) 1.454(4) 1.32q4) 1.306(4) C8B N2B C9B C9B C15B C15B C14B C13B C12B C11B N4B C17B C18B C18B C19B C20B C21B C22B N6B C25B C32B C32B C31B C31B C26B C27B C28B C29B C2B C2B C7B C6B C5B C4B C7B C9B N3B ClOB C14B ClOB C13B C12B CllB C 10B C17B C18B C19B C23B C20B C21B C22B C23B C25B C26B N8B C31B C26B C30B C27B C28B C29B C30B C7B C3B C6B C5B C4B C3B 1.444(4)1.3 19( 3) 1.377( 4) 1.438(4) 1.394(4) 1.383(4) 1.382( 5) 1.375( 5) 1.3 87( 4) 1.404(5)1.3 1 2( 4) 1.448(4) 1.397(4) 1.376(5) 1.367(6) 1.377(6) 1.379(4) 1.389(5) 1.3 13(3) 1.448(4) 1.315(4) 1.437(5) 1.385(4) 1.400(5) 1.392( 5) 1.367(5) 1.382(5) 1.392(6) 1.356(6) 1.423(5) 1.397( 6) 1.367( 6) 1.386(8) 1.3 72( 7) " Numbers in parentheses are estimated standard deviations in the least significant digits.Table 4 Table of bond angles around Zr atom in degrees" Table 5 Comparison of displacements of the outermost carbon atoms ~~ ~~ ~~~~~ of each phenyl ring for some [M(pc),] and [M(pc)(pc.)] structures atom 1 atom 2 atom 3 angle least displaced most displaced refs. N1A Zr N3A 72.19(8) compound carbon atom/A carbon atom/A NlA Zr N5A 113.57(9) N1A Zr N7A 73.37(8) Ca-Sn(pc),I 0.18 1.01 8 N1A Zr N7B 146.42(8) [U(PC)21 0.49" 1.10" 12,13( b) NlA Zr N1B 139.21(9) CTh(PC),l 0.27 1.30 13(b)N1A Zr N5B 81.2q9) CLU(PCMPC.)I 0.25 1.10 10 N1A Zr N3B 76.42(8) CZr(pc),I 0.49 1.47 this work N3A Zr N5A 73.18( 7) N3A Zr N7A 114.16(9) " Calculated from data from the Cambridge database using COSMIC.N3A Zr N7B 81.42(9) N3A Zr N1B 146.85(8) N3A Zr N5B 75.96(8) which to measure it, though most of the angles lie between N3A Zr N3B 138.34( 7) N5A Zr N7A 71.98(8) 37 and 45". N5A Zr N7B 76.7q9) The distortions in the [Zr(pc)J structure are even noticeable N5A Zr N1B 81.49( 7) in the pc rings themselves (Table4). The atoms given in N5A Zr N5B 138.88(9) Table6 are defined as in the legend. The Niso-C, bond N5A Zr N3B 146.27(8) distances are similar to the other structures though theN7A Zr N7B 138.1 5( 7) 76.42(9) C,-C,, C,-C,, Ca-NiSO and Cphe-Cphe bond distancesN7A Zr N1B N7A Zr N5B 147.18(8) are all shorter.There are also some significant differences in N7A Zr N3B 81.23(8) the bond angles especially the C,-NiSo-C, and Nis0-C,-C, N7B Zr N1B 72.06( 9) angles. These findings are in keeping with the severe wok-like N7B Zr N5B 72.38(8) distortions found in the rings. N7B Zr N3B 1 13.60(9) It is worth noting at this point that, though this is the most NIB Zr N5B 112.99(9) distorted [M(pc),] structure to date, the pc rings are neutral, N1B Zr N3B 72.42(7) N5B Zr N3B 72.76(8) and not one electron oxidised, as found and discussed for [Lu(pc)(pc.)]lo. Thus ring distortion does not infer the pres- Numbers in parantheses are estimated standard deviations. ence of a pc radical; clearly large distortion can be a factor J.MATER. CHEM., 1991, VOL. 1 Table 6 Lengths and angles found in isoindole moieties of metallo-bisphthalocyanines a-Sn(pc)," U(PC)Zb U(PC)ZC Th(PC)Z' P-Nd(pcM~c*)~ LU(PCHPC*Y P-Zr(~c)z 1.375(6) 1.467(9) 1.387(8) 1.32 1 (7) 1.409(9) 108.1(7) 109.2( 4) 106.6(5) 128.7(5) 12 1.8( 6) 122.7(4) 115.3(6) 1 2 1.8( 7) 1.38(1) 1.46( 1) 1.4q 1) 1.32(1) 107.9(7) 109.4(7) 106.6(7) 127.6(7) 1 23.9( 7) 12 1.6(7) 116.8(7) 12 1 S(7) 1.40(1) 1.37 1.48 1.40 1.33 1.40 107.9 110.2 105.8 127.1 124.5 122.0 117.5 121.2 1.38 1.49 1.39 1.32 1.41 108.2 110.8 104.8 128.0 123.6 120.9 118.7 121.4 1.377(5) 1.472( 6) 1.398(8) 1.344(5) 1.40 1( 6) 107.5(4) 109.8( 3) 106.3( 3) 127.4(3) 123.2(9) 122.1(4) 116.2(4) 12 1.7(4) 1.376(3) 1.456(2) 1.390(4) 1.327(2) 1.389(3) 107.6(2) 109.6(2) 1 06.5( 2) 127.5( 3) 123.0(4) 12 1.2( 2) 117.3(3)12 1.2( 5) 1.3 75( 6) 1.445(5) 1.377( 7) 1.3 18( 5) 1.386(6) 106.1( 3) 11042) 106.5(4) 128.q5) 121.5( 3) 1 2 1.3( 5) 1 18.0(8) 12 1.8(4) " Ref.(8); ref. (12); 'ref. 13 (b); ref. 9(b); ref. (10). Numbers in parentheses are estimated standard derivatives; when not present, these are not given in the original papers. Niso=nitrogen atom of the isoindole groups; C, =a carbon atom of the isoindole group with respect to Niso; C, =P carbon atom of the isoindole group with respect to Niso;Cphe=phenyl carbon atom; N,= methine nitrogen atom. Table 7 Comparison of [M(pc),] and [M(pc)(pc)] structures mean N, plane to staggering average mean N4 plane angle of M-N bond Electrochromism and Cyclic Voltammetry We have previously described the colours and spectra ob- served on reduction of thin films of [Zr(pc),] on IT0 glass." The reaction that takes place is CZr(pc),l+ e --+ CZr(pc),l-cyan purple-red The spectral changes between neutral and reduced forms are reversible and more than lo3 colour cycles can be achieved.We have also reported that on oxidation an irreversible loss of colour of the film takes place, and we presented the spectra that show the colour loss." We now report some cyclic voltammograms that add to these data. The cyclic voltammograms for [Zr(p~)~] are presented in Fig. 2. The first cycle has two current peaks on the forward scan at -1.09 and -1.17 V, and one return wave at -0.75 is observed.On the second cycle a single current maximum is apparent at -1.05 V and it has a return wave at -0.69 V. A small maximum at -0.58 V can also be distinguished on the second forward scan, but this has no apparent return wave. The voltammograms show that the reduction of [Zr(pc),] occurs near the limit of the negative potential range of IT0 coated glass in aqueous solution. The very sharp peak on the first scan is typical of ion penetration of the film,23 though this is normally simultaneous with the reduction of the film material. An alternative expla- nation for the very sharp nature of this wave is that it represents a polarographic stripping wave which suggests the reduction of metal ions in the film. This type of wave, however, neither appears in the bare Cr/Au electrode nor is observed 001 mAI500 mV s-' / P +05 0 potential/\/ Fig.2 Cyclic voltammograms of a [Z~(pc)~] film on an Au electrode. (-) Initial scan showing ion penetration; (---) second cycle distance/A CTh(PC)Z1 2.96 CNd(pcHpc*)l 2.94 CU(PC),l 2.81 CLU(PC)(PC)l 2.69 Ca-Sn(Pc)zl 2.70 CZr(PC)zl 2.20" rings/" distance/A ref. 37 2.48 13" 38 2.47 9b 37 2.43 12 45 2.38 10 42 2.35 8 42 2.30 this work a Calculated from GEOSTAT. of structure alone. Here it is forced by the binding of the Zr atom. It is therefore obvious that in [M(pc),] and [M(pc)(pc.)] structures the bonding of the Nisoatoms to the metal must significantly distort the rings. There are not many Zr" structures known in which the Zr" cation is bonded to eight nitrogen atoms.In fact, in the Cambridge Crystallographic Database there are only two. One of these, tetraisothiocyanatobis(2,2'-bipyridine)zirconium(1~) [Zr(NCS)4(CloHsN2)2],20 has an 'average' Zr-N bond length of 2.297(4) 8, and is close to a D2d dodecahedron in structure. The other structure bis(2,2'-bi-2-2-thiazoline)tetrabis-(isothiocyanato) zirconium(1v) [Zr(NCS)4(C6H8N2S2)]21 has an average Zr-N bond length of 2.284(5) 8, and is intermedi- ate between an ideal dodecahedron and an ideal square antiprism. In both these structures each Zr" cation is sur- rounded by four monodentate and two bidentate ligands. The Zr" cation can thus dictate its geometry much more freely in these complexes than it can in [Zr(pc),].So it would appear that it is the presence of the two pc ligands that forces a square antiprismatic structure on the Zr" cation, and usually this early heavy transition metal much prefers dodecahedra1 co-ordination. The latter is particularly true for Zr" in non- nitrogen atom or partial nitrogen eight co-ordination. From Table 2 it is clear that our [Zr(pc),] is equivalent to the /3 phase of [Sn(pc),].17 It is clear that the [Zr(pc),] is not isostructural with c~-[Sn(pc)].~ These findings are in agreement with the fact that our crystals were grown by sublimation techniques. We have not compared this structure to those of the reduced lutetium phthalocyanines reported by Moussavi et a[.," as the latter are said to be influenced by the presence of the cation.We note that the protonated structure is very similar to that of the [Lu(pc)(pc.)] compound discussed here. in other phthalocyanine films deposited by vacuum subli-mati~n.~~ The voltammogram obtained by continuously cycling a [Zr(pc),]-coated Au electrode shows the same general features as seen in the second scan in Fig. 2. It was found that the features of the second scan remain, and that the current passed by the electrode falls continuously as the number of cycles increases. This is typical of observations made on similar materials23 and is due to the swelling of the films during the electrochromic process once ion penetration has been initiated. Visually, the electrochromic process continues throughout the cycling.On films on IT0 glass the cyclic voltammograms show similar behaviour in the same voltage range. On the first cycle ion penetration is again observed as a peak at -1.40 V and there is a broad return wave centred at -0.65 V. On the second scan reduction is observed at -1.2 V and the return wave is again broad. The greatest current loss is between the first and second cycle which is further evidence for the assignment of the first peak to ion penetrati~n.~~ If the voltage range is increased to +1.2 to -1.5 V (Fig. 3), then several new peaks are seen on the voltammogram. The peaks indicating reduction and reoxidation of the film to neutral are in keeping with those described previously. One new current peak is observed on the forward scan at f1.00 V and two peaks are seen on the reverse scan at -0.68 and +0.12 V.The peak at +1.O V is indicative of oxidation of the [Zr(p~)~]film and the two return peaks are reduction to the neutral state. Upon repeated cycling there is a rapid decrease in the current of both oxidation and reduction. On oxidation, the film goes first colourless, then a faint red is observed, which in turn returns colourless and then cyan- blue as the cycle continues towards neutral voltage. We have shown that if the films are cycled between +1,2 and -1.2 V more than about 30 times, they fade completely. We believe that the fading is due to the pc rings being chemically degraded (possibly by ring opening) on oxidation.We have suggested15 that the presence of MIv ions destabilises the pc rings owing to their polarising power (in the case of lanthanide ions many cycles can be achieved"). This explanation would be ia keeping with the highly distorted ring structure found for CZr(pc)*l.The exact nature of the destruction has not been elucidated but it is probably due to attack on the nitrogen bridges of the pc rings by OH-ions as has been previously suggested for [Lu(pc)(pc.)] films.' The very distorted [Zr(pc),?] molecules are more open to OH-ion attack at these positions than the less distorted [Lu(pc)(pc.)]. Fig. 3 Cyclic voltammogram of [Zr(pc),] film on ITO-coated glass. Reduction and oxidation peaks can be seen; there is a rapid decrease in current upon repeated cycling J.MATER. CHEM., 1991, VOL. 1 All the values quoted on IT0 were for a scan rate of 200 mV s-';peak positions varied at other scan rates. Collins and Schiffrin' have described peak-current dependence on sweep-rate for [Lu(pc)(pc.)] for both oxidation and reduction sweeps. They suggest that the shift in the voltammograms with change of scan rate is due to uncompensated cell resistance. We agree with their interpretation that the films behave as potential-dependent capacitors. In addition, such effects will be dependent on film thickness. The thickness of the films used were measured using a Tencor a-step 100 step height measuring device. All our films were between 1000 and 3000 8, thick.Conclusions The [Zr(pc),] structure contains the most distorted pc rings yet reported. The extreme wok-like ring distortions found in this compound are caused by their binding to the small Zr" cation. This cation has a large polarising power which causes the complex to be destroyed when it is oxidised. The mechan- ism of ring opening on oxidation probably involves OH-ions reacting with the exposed nitrogen bridges at the periph- ery of the pc rings.' We have found no evidence for the involvement of the metal in the electrochemical processes. J. S. thanks the British Technology Group for their continued support in this area and for studentships to P.L. and S.D.H. References (a) 1. S. 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Frenz and Associates Inc., College Station, Texas, USA. W. J. Kroenke and M. E. Kenny, Inorg. Chem., 1964, 3, 696. J. MATER. CHEM., 1991, VOL. 1 35 18 19 20 M. Gouterman, in The Porphyrins, ed. D. Dolphin, Academic Press, New York, 1978, vol. 3, pp. 1-165. R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751. E. J. Peterson, R. B. Van Dreel and T. M. Brown, Znorg. Chem., 1976, 15, 309. 22 23 24 M. Moussavi, A. de Cian, J. Fischer and R. Weiss, Znorg. Chem., 1988, 27, 1287. H. Abruna, Coord. Chem. Rev., 1988,86, 135. J. Silver, P. Lukes and S. D. Howe, unpublished results. 21 R. A. Johnson, R. B. Van Dreel and T. M. Brown, Inorg. Chem., 1984, 23, 4302. Paper 0/02753G; Received 20th June, 1990