\
PERGAMON Polyhedron 07 "0888# 520Ð539
9166!4276:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[ PII] S 9 1 6 6 ! 4 2 7 6 " 8 7 # 9 9 2 9 7 ! 7
Chemistry of 1!"arylazo#phenolate complexes of ruthenium[
Synthesis\ structure and reactivities
Kanchana Sui
a\ Shie!Ming Peng
b\ Samaresh Bhattacharya
a\aDepartment of Chemistry\ Inorganic Chemistry Section\ Jadavpur University\ Calcutta 699 921\ India bDepartment of Chemistry\ National Taiwan University\ Taipei\ Taiwan\ R[O[C[
Received 05 June 0887^ accepted 5 August 0887
Abstract
A group of six ruthenium"III# complexes of type ðRu"acac#"L#1Ł\ where acac acetylacetonate anion and L 1!"arylazo#!3!
methylphenolate anion or 0!"phenylazo#!1!naphtholate anion\ have been synthesized and characterized[ Structural characterization of a representative complex\ where L 0!"phenylazo#!1!naphtholate anion\ shows that the azophenolate ligands are coordinated as N\O!donor ligands forming six!membered chelate rings[ The complexes are paramagnetic "low!spin d4\ S 0:1# and show rhombic
ESR spectra in 0]0 dichloromethaneÐtoluene solution at 66 K[ In carbon tetrachloride solution\ these complexes show intense LMCT transitions in the visible region together with weak ligand!_eld transitions in the near!IR region[ All the complexes display two cyclic voltammetric responses\ a ruthenium"III#Ðruthenium"IV# oxidation in the range of 9[72 to 0[92 V vs SCE and a ruthenium"III#Ð ruthenium"II# reduction in the range of −9[13 to −9[41 V vs SCE[ Formal potentials of both the couples correlate linearly with the Hammett constant of the para substituent in the arylazo fragment of the 1!"arylazo#!3!methylphenolate ligand[ The ruthenimn"IV# and ruthenium"II# congeners of the ðRuIII"acac#"L#
1Ł complexes have been generated by chemical or electrochemical methods and
they have been characterized by electronic spectroscopy and cyclic voltammetry[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
Keywords]Ruthenium^ 1!"arylazo#phenolates^ Synthesis^ Structure^ Reactivities
0[ Introduction
The chemistry of ruthenium has been a center of immense interest ð0Ł\ largely because of the fascinating reactivities exhibited by its complexes[ It is the nature of the ligands\ which surround the metal\ that dictates the properties of the complexes[ Coordination of ruthenium by ligands of di}erent types is of signi_cant importance in this respect[ In the present work\ which has originated from our interest in the chemistry of ruthenium in di}er! ent coordination environments ð1Ł\ we have used 1!"ary! lazo# phenols "0# as the principal ligand[ The interest behind the choice of these ligands is two!fold[ Firstly\ it contains two potential donor sites\ viz[ azo nitrogen and phenolate oxygen\ which are of opposite natures[ The azo group has a strong p!acid character and coordination by azo nitrogen stabilizes ruthenium in the lower oxi! dation states ð2Ł\ while phenolate oxygen is a hard base and coordination by it is known to stabilize the higher oxidation states of the same metal ð3Ł[ Secondly\ these
Corresponding author[
ligands display di}erent coordination modes upon com! plex formation[ The 1!"arylazo#phenol ligands are known to coordinate metal ions usually as a bidentate N\O! donor\ via dissociation of the phenolic proton\ forming a six!membered chelate ring "1# ð4Ł[ However\ we have recently observed that they also form _ve!membered che! late ring "2# under sterically forced conditions ð5Ł[ These ligands are also known to coordinate metal ions as dianionic tridentate C\N\O!donors "3# a}ording organ! ometallic complexes ð6Ł[ It may be mentioned here that the ruthenium chemistry of these ligands has not been much explored ð7Ł[ Herein\ we have restricted our studies
to some bis!1!"arylazo#phenolate complexes of
ruthenium\ where acetylacetonate anion has served as the coligand[ The synthesis of a series of mixed tris complexes\ their characterization including structure determination and their reactivities are described in this paper[ Six 1!"arylazo#phenols\ which are abbreviated in general as HL\ where H stands for dissociable phenolic proton\ have been used in the present study[ Speci_c abbreviations are shown in structure 4[ In the 1!"arylazo#! 3!methylphenols\ the substituent R is systematically varied in order to study their in~uence on the redox properties of the complexes[
1[ Experimental 1[0[ Materials
Commercial ruthenium trichloride\ purchased from Arora Matthey\ Calcutta\ India was converted to RuCl2=2H1O by repeated evaporation with concentrated
hydrochloric acid[ ðRu"acac#2Ł "acac acetyl!
acetonate ion# was prepared by following a reported pro! cedure ð8Ł[ The 1!"arylazo#phenol ligands were prepared by coupling diazotized anilines with p!cresol or b!naph! thol[ Puri_cation of acetonitrile and preparation of tetra! ethylammonium perchlorate for electrochemical work were performed as before ð1Ł[ All other chemicals and solvents were reagent grade commercial materials and were used as received[
1[1[ Physical measurements
Microanalyses "C\ H\ N# were performed using a Per! kin!Elmer 139C elemental analyzer[ IR spectra were obtained on a Perkin!Elmer 672 spectrometer with sam! ples prepared as KBR pellets[ Electronic spectra were recorded on Hitachi U 2490 and Shimadzu UV 139 spec! trophotometers[ Magnetic susceptibilities were measured using a PAR 044 Vibrating sample magnetometer[ X! band ESR spectra were recorded on a Varian E!098C spectrometer _tted with a quartz Dewar for measure! ments at 66 K "liquid nitrogen# and the spectra were calibrated with DPPH "` 1[9926#[ Electrochemical measurements were made using a PAR model 162 Potent! iostat[ A platinum disc working electrode "of area 9[91 cm1
#\ a platinum wire auxiliary electrode and an aqueous saturated calomel reference electrode "SCE# were used in a three electrode con_guration[ A platinum! wire gauge working electrode was used in the coulometric experiments[ Dinitrogen gas was puri_ed by successively bubbling it through alkaline dithionite and concentrated sulphuric acid[ All electrochemical experiments were per! formed under a dinitrogen atmosphere and elec! trochemical data were collected at 187 K and are uncorrected for junction potentials[ A RE 9978 XÐY recorder was used to trace the voltammograms[
1[2[ Preparations
The ðRu"acae#"L#1Ł complexes were synthesized fol!
lowing a general procedure[ Speci_c details for one com! plex are given in next section[
1[2[0[ ðRu"acac#"ap!H#1Ł
ðRu"acac#2Ł "099 mg\ 9[14 mmol# and Hap!H "219 mg\
0[4 mmol# were taken in 19 cm2ethylbenzoate[ The mix!
ture was heated at 059>C with continuous passage of nitrogen to remove the volatile acetylacetone[ Heating was continued for 5 h and the colour of the solution
gradually became brown[ The solvent was then evap! orated under reduced pressure[ The crude product was dissolved in hexane and was subjected to chro! matography on a silica gel "59Ð019 mesh# column[ On elution with hexane and 1]0 hexane]benzene mixture as eluent\ yellow and light red bands came out and were rejected[ With a 0]3 hexane]benzene mixture as the next eluent\ a deep brown band came out[ This was collected and evaporation of the eluate gave ðRu"acac#"ap!H#1Ł as
a dark brown microcrystalline solid[ The yield was 54) "091 mg#[
1[2[1[ ðRu"acac#"an!H#1Ł
ðRu"acac#"an!H#1Ł was prepared using the same above
procedure with slight modi_cation in the puri_cation method[ The crude sample was dissolved in a minimum amount of dichloromethane and chromatographed through a silica gel column[ Initial yellow and faint red bands\ which came out with hexane and a 2]0 hexane] benzene mixture as eluents\ were rejected[ With 1]0 hexane] benzene as the eluent\ a deep brown band came out and was collected[ Evaporation of the eluate gave the pure compound[ The yield was 57) "008 mg#[
1[3[ Crystallography
Single crystals of ðRu"acac#"an!H#1Ł were grown by
slow evaporation of a 0]0 acetoneÐisopropanol solution of the complex[ Selected crystal data and data collection parameters are given in Table 0[ Data were collected on a Siemens Smart CCD di}ractometer using graphite! monochromated Mo!Karadiation "l 9[60962 A # by uÐ
1u scans[ The standard re~ections\ used to check the crystal stability towards X!ray exposure\ showed no sig!
Table 0
Crystallographic data for ðRu"acac#"an!H#1Ł
Empirical formula C26H18N3O3Ru fw 583[60 Space group P10:n a"A # 00[8512"1# b"A # 02[6706"1# c"A # 08[4414"2# a "># 89 b "># 092[363"0# g "># 89 V"A2# 2023[61"7# Z 3 rcalc"mg m−0# 0[361 l "A # 9[60962 Crystal size "mm# 9[19×9[97×9[94 T"K# 184"1# m "mm−0# 9[437 R0 9[9378 wR1 9[9763 GOF 0[943
ni_cant intensity variation over the entire course of data collection[ X!ray data reduction and structure solution and re_nement were done using the NRCVAX package[ The structure was re_ned by full!matrix least!squares on F1[ Final cycles of re_nement converged with discrepancy
indices of R0 9[9378 and wR1 9[9763[
2[ Results and discussion
Reaction of the 1!"arylazo#phenol ligands "HL# with tris!"acetylacetonato# ruthenium"III# a}orded bis!com! plexes of type ðRu"acac#"L#1Ł where two acetylacetonate
ligands were replaced by the 1!"arylazo#phenolate ligands while one acetylacetonate is still retained[ Formation of similar mixed ligand tris chelates\ via incomplete dis! sociation of acetylacetonates from ðM"acac#2Ł\ is known
for ruthenium ð09Ł as well as other metals ð00Ł[ Elemental "C\ H\ N# analytical data "Table 1# of these ðRu"acac#"L#1Ł
complexes are in good agreement with their compo! sitions[ As acetylacetonate is a bidentate ligand and
Table 1
Microanalytical\ magnetic moment and electronic spectral data of the ðRuIII"acac#"L#
1Ł complexes
Compound Microanalytical dataa")# m
e} Electronic spectral databl "nm# "o\ M−0cm−0#
"BM# C H N ðRu"acac#"ap!OCH2#1Ł 46[7 "47[0# 3[7 "3[7# 7[9 "7[1# 0[82 197 "62399#\ 149c"20999#\ 234 "06499#\ 316 "03999#\ 620c"1399#\ 0119 "103#\ 0449c"098# ðRu"acac#"ap!CH2#1Ł 59[4 "59[8# 4[9 "4[0# 7[4 "7[5# 0[76 109 "28999#\ 149c"14299#\ 205 "06299#\ 311 "00299#\ 579c"1299#\ 0159 "110#\ 0560c"022# ðRu"acac#"ap!H#1Ł 59[3 "48[7# 3[8 "3[6# 8[0 "8[9# 0[89 101 "32299#\ 141c "1399#\ 291 "19099#\ 315 "00599#\ 573c"1099#\ 0225 "082#\ 0699c"014# ðRu"acac#"ap!Cl#1Ł 42[0 "42[7# 2[6 "2[8# 7[9 "7[0# 0[74 107 "22199#\ 145c"10999#\ 183 "08999#\ 325 "00099#\ 695c"1099#\ 0129 "040#\ 0507c"70# ðRu"acac#"ap!NO1#1Ł 41[5 "41[1# 3[9 "2[7# 00[8 "00[7# 0[78 109 "27399#\ 141c "11299#\ 219 "19599#\ 342 "8999#\ 633c"0399#\ 0299 "72#\ 0699 "46# ðRu"acac#"an!H#1Ł 53[3 "53[9# 3[1 "3[1# 7[2 "7[0# 0[89 117 "55199#\ 159c"28099#\ 205 "16299#\ 269 "05699#\ 354 "06999#\ 797c"0899#\ 0324 "235#\ 0899 "182# aCalculated values are in parentheses[
bIn carbon tetrachloride solution[ cShoulder[
ruthenium is usually octahedrally coordinated\ this indi! cates that the 1!"arylazo#phenolates are coordinated as bidentate ligands "as in 1 or 2#[ As the 1!"ary! lazo#phenolates are unsymmetrical bidentate ligands\ the ðRu"acac#"L#1Ł complexes may\ in principle\ exist in three
di}erent geometrical isomeric forms "5\ 6 and 7#[ Molecular structure of a representative complex\ viz[ ðRu"acac#"an!H#1Ł has been solved by X!ray crys!
tallography[ The structure is shown in Fig[ 0 and selected bond distances and angles are given in Table 2[ The 0! "phenylazo#naphtholate ligands are coordinated as bidentate N\O!donor ligand forming six!membered che! late rings "as in 1# with a bite angle of ½89>[ The coor! dination sphere around ruthenium is N1O3 which is
slightly distorted from ideal octahedral geometry as re~ected in the bond angles[ The azo nitrogens occupied transpositions and the phenolate oxygens\ cis positions[ Therefore\ structure determination shows that ðRu "acac# "an!H#1Ł has structure 5[ The reason for the nitrogens to
be in the trans position is probably steric in nature[ A bulky phenyl group is linked to this nitrogen and rotation
of this ring around the CÐN bond is allowed[ With two such nitrogens in the cis positions "as in 6 and 7#\ severe steric interaction between these phenyl rings appears to be highly probable[ The RuÐN and RuÐO distances are as usually observed in complexes of ruthenium"III# ð3bŁ[ The azo NÐN distances in ðRu"acac#"an!H#1Ł are longer
than uncoordinated azo "N1N# distances ð01Ł[ However\
they are similar to those observed in other structurally characterised azo complexes of trivalent ruthenium ð6\02Ł[ The phenolic CÐO distances are also quite normal ð3b\6Ł[ The bond distances in the Ru"acae# fragment com! pare well with those found in other complexes containing the RuIII
"acac# moiety ð03a\03bŁ[ As the properties of all six ðRu"acac#"L#1Ł complexes are similar "vide infra#\ the
other _ve ðRu "acac#"L#1Ł complexes are assumed to have
a similar structure as ðRu"acac#"an!H#1Ł[
Infrared spectra of the ðRu"acac#"L#1Ł complexes are
very similar[ Each shows many vibrations of di}erent intensities below 0699 cm−0
[ No attempt has been made for individual band assignment[ However\ comparison with the infrared spectrum of ðRu"acac#2Ł shows the pres!
ence of additional vibrations in the spectra of ðRu "acac#"L#1Ł complexes\ which are indicative of the pres!
ence of 1!"arylazo#phenolate ligands[ The ðRu"acac#"L#1Ł
complexes are soluble in common organic solvents like acetonitrile\ acetone\ hexane\ carbon tetrachloride\ etc[\
Fig[ 0[ View of the ðRu"acac#"an!H#1Ł molecule[
producing solutions with di}erent shades of brown[ Elec! tronic spectra of these complexes were recorded in carbon tetrachloride solution[ Spectral data are displayed in Table 1 and a selected spectrum is shown in Fig[ 1[ The spectral properties of all six complexes are similar[ Each complex shows several intense absorptions in the visible region which are probably due to ligand!to!metal charge! transfer transitions[ They also show two weak transitions in the near!IR region\ the origin of which will be discussed below[
Magnetic susceptibility measurements show that the ðRu"acac#"L#1Ł complexes are one!electron paramagnetic
"Table 1#\ which is in accordance with the ¦2 state of ruthenium "low!spin d4
\ S 0:1# in these complexes[ ESR spectra of the ðRu"acac#"L#1Ł complexes were recorded
in a 0]0 dichloromethaneÐtoluene solution at 66 K[ A representative spectrum is shown in Fig[ 2[ Each complex shows a rhombic spectrum with three distinct g!values "Table 3#[ However\ all the spectra may be regarded as pseudo!axial\ consisting of two very closely spaced signals "g0and g1\ rhombic component of g_# and a rather iso!
lated signal "g2\ g> in the axial case#[ Hence the axial
distortion "D# that splits the t1 level into a and e
components\ is expected to be much larger than the rhom! bic distortion "V# which splits e[ This splitting pattern is illustrated as an inset in Fig[ 2[ Spin!orbit coupling causes
Table 2
Selected bond distances and bond angles for ðRu"acac#"an!H#1Ł
Bond distances "A #
RuÐO"0# 0[862"1# C"23#ÐO"2# 0[Ð166"3# RuÐO"1# 0[862"1# C"23#ÐC"24# 0[279"5# RuÐO"2# 1[908"1# C"24#ÐC"25# 0[271"5# RuÐO"3# 1[913"1# C"25#ÐO"3# 0[179"3# RuÐN"0# 1[925"2# RuÐN"2# 1[926"2# Bond angles "># O"1#ÐRuÐO"2# 067[03"8# O"0#ÐRuÐO"3# 064[52"09# N"0#ÐRuÐN"2# 068[24"00# O"0#ÐRuÐO"1# 84[53"09# O"2#ÐRuÐN"0# 77[65"09# O"0#ÐRuÐO"2# 74[38"8# O"3#ÐRuÐN"0# 80[55"09# O"1#ÐRuÐO"3# 77[27"09# O"0#ÐRuÐN"2# 78[37"09# O"2#ÐRuÐO"3# 89[42"09# O"1#ÐRuÐN"2# 78[71"8# O"0#ÐRuÐN"0# 89[97"09# O"2#ÐRuÐN"2# 80[57"8# O"1#ÐRuÐN"0# 78[64"09# O"3#ÐRuÐN"2# 77[70"09#
Fig[ 1[ Electronic spectra of ðRuIII"acac#"ap!H#
1Ł "***\ in carbon tetrachloride solution#\ ðRuII"acac#"ap!H#1Ł−"! ! !\ in acetonitrile solution# and
ðRuIV"acac#
1"ap!H#1Ł¦"Ð= Ð\ in acetonitrile solution#[
further changes in the energy gaps[ Two electronic tran! sitions "transition energies DE0and DE1^ DE0³DE1# are
therefore possible within these three levels[ All the energy parameters have been computed "Table 3# using the observed g!values\ g!tensor theory of low!spin d4
com! plexes ð04a\04bŁ and a reported method ð05Ł[ The axial distortion is indeed much larger than the rhombic one for all the six complexes[ Taking the spin!orbit coupling constant "l# of complexed ruthenium"III# to be 0999 cm−0
ð05Ł\ the DE0and DE1transitions are expected to appear
near 5999 and 7999 cm−0\ respectively[ Both transitions
were experimentally observed\ at energies very close to the theoretically predicted values "Table 3#\ as two rela! tively weak absorptions "Table 1\ Fig[ 1#[ The ESR data
analysis thus indicates that the ðRu"acac#"L#1Ł complexes
are distorted from ideal octahedral geometry\ as also observed from the X!ray structure determination of ðRu"acac#"an!H#1Ł[
Electron!transfer properties of the ðRu"acac#"L#1Ł com!
plexes were studied in acetonitrile solution "9[0 M TEAP# by cyclic voltammetry[ Voltammetric data are presented in Table 4 and a selected voltammogram is shown in Fig[ 3[ Each complex shows two voltammetric responses\ one oxidative response on the positive side of SCE and another reductive response on the negative side\ which are respectively assigned to the ruthenium"III#Ð ruthenium"IV# and ruthenium"III#Ðruthenimn"II# couples "eqs[ "0# and "1##[
Table 3
ESR g!valuesaand derived parametersbof the ðRu"acac#"L#
1Ł complexes Compound g0 g1 g2 D:l V:l DE0:lc DE1:lc ðRu"acac#"ap!OCH2#1Ł 1[030 1[006 0[827 5[65 9[76 5[14 "5[34# 6[49 "7[19# ðRu"acac#"ap!CH2#1Ł 1[041 1[019 0[827 5[72 0[00 5[12 "4[87# 6[55 "6[83# ðRu"acac#"ap!H#1Ł 1[041 1[013 0[839 5[82 0[99 5[26 "4[77# 6[62 "6[37# ðRu"acac#"ap!Cl#1Ł 1[055 1[003 0[827 5[83 0[74 5[91 "5[07# 7[97 "7[02# ðRu"acac#"ap!NO1#1Ł 1[030 1[003 0[830 5[84 0[94 5[26 "4[77# 6[66 "6[58# ðRu"acac#"an!H#1Ł 1[050 1[006 0[828 5[82 0[45 5[03 "4[15# 6[84 "5[86# aIn 0]0 dichloromethaneÐtoluene solution at 66 K[
bSpin!orbit coupling constant "l# for complexed Ru"III# is ½0999 cm−0[ cThe experimentally observed values "see Table 1# are given in parentheses[
Fig[ 2[ ESR spechm of ðRu"acac#"ap!CH2#1Ł in 0]0 dichlo!
romethane]toluene at 66 K[
Table 4
Cyclic voltammetric dataa
Compound E0:1"V# "DEp\ mV#
RuII:RuIII RuIII:RuIV
ðRu"acac#"ap!OCH2#1Ł −9[41"59# 9[76"69# ðRu"acac#"ap!CH2#1Ł −9[49"69# 9[78"59# ðRu"acac#"ap!H#1Ł −9[36"59# 9[80"59# ðRu"acac#"ap!Cl#1Ł −9[30"69# 9[84"59# ðRu"acac#"ap!NO1#1Ł −9[20"59# 0[92"69# ðRu"acac#"an!H#1Ł −9[13"59# 9[72"59# aConditions] solvent\ acetonitrile^ supporting electrolyte\ TEAP
"9[0 M#^ working electrode\ platinum^ auxiliary electrode\ platinum] reference electrode\ SCE] solute concentration\ ½09−2M^
E0:1 9[4"Epa¦Epc#\ where Epaand Epcare anodic and cathodic peak
potentials^ DEp Epa−Epc^ scan rate 49 mV S−0[
ðRuIII"acac#"L#
1Ł gh ðRuIV"acac#"L#1Ł¦¦e− "0#
ðRuIII "acac#"L#1Ł¦e −gh ðRuII "acac#"L#1Ł − "1# Both responses are reversible with a peak!to!peak sep! aration of 59Ð69 mV[ The one!electron nature of these couples are established by constant potential coulometry "vide infra#[ It may be noted here that the ruthenium"III#Ð ruthenium"IV# and ruthenium"III#Ðruthenium"II# poten! tials of these ðRu"acac#"L#1Ł complexes are much lower
than those in the ðRu"bpy#"L#1Ł "bpy 1\1?!bipyridine#
complexes ð7cŁ\ which is due to the hard nature of the acetylacetonate oxygens compared to the soft nitrogens in bpy[
Potentials of both the ruthenium"III#Ðruthenium"II# and ruthenimn"III#Ðruthenium"IV# couples in these ðRu"acac#"L#1Ł "L the 1!"arylazo#!3!methylphenolate
ligands# complexes are found to be sensitive to the nature of the substituent R[ With increasing electron!with! drawing character of R\ the formal potentials "E0:1# of
both couples increase[ The plot of the E0:1 values vs 1s
"where s is the Hammett constant of R ð06Ł# are linear "Fig[ 4#[ The slope of these lines\ which is known as the reaction constant r ð07Ł and is a measure of the sensitivity of E0:1 with R\ is 9[97 for the ruthenium"III#Ð
ruthenium"IV# couple and 9[09 for the ruthenium"III#Ð ruthenium"II# couple[ It is clear from these plots that the ruthenium"III#Ðruthenium"II# couple is more in~uenced by R compared to the ruthenium"III#Ðruthenium"IV# couple[ It is also interesting to note that a single substitu! ent\ which is six bonds away from the electroactive metal center\ can in~uence the metal!centred redox potentials in a predictable manner[
From the reversible nature of both ruthenium"III#Ð ruthenium"IV# and ruthenium"III#Ðruthenium"II# couples\ it appeared that both the oxidized species\ i[e[ðRuIV
"acac#"L#1Ł ¦
and the reduced species\ i[e[ðRuII
"acac#"L#1Ł−\ might be stable on longer time scales[ To
investigate this\ ðRu"acac#"L#1Ł was coulometrically oxi!
dized near 0[1 V vs SCE[ The oxidations have been smooth and quantitative with n½0 ðn"number of electron transfer# Qf:Qc\ where Qc calculated Coulomb count
Fig[ 3[ Cyclic voltammogram of ðRu"acae#"ap!NO1#1Ł in acetonitrile solution "9[0 M TEAP# at a scan rate of 49 mV S−0[
Table 5
Electronic spectral dataaof the ðRuII"acac#"L#
1Ł−and ðRuIV"acac#"L#1Ł¦complexes l "nm# "o\ M−0cm−0#
L ðRuII"acac#"L# 1Ł− ðRuIV"acac#"L#1Ł¦ ap!OCH2 129 "89699#\ 219b"11399#\ 393 "06399#\ 414 "00799#\ 693b"4299# 101 "35799#\ 149b"18999#\ 233 "05599#\ 313 "03499#\ 579b "1299# ap!CH2 121 "095099#\ 297b"14099#\ 399 "05399#\ 429 "00699#\ 699b"4599# 101 "35799#\ 141b"17199#\ 205 "08499#\ 319 "02399#\ 541b "1599# ap!H 114 "089999#\ 293b"11199#\ 397 "00399#\ 439 "7199#\ 697b"2599# 101 "62099#\ 149b"28399#\ 293 "18999#\ 313 "04599#\ 545b "2299# ap!Cl 117 "09399#\ 173b"27599#\ 285 "06499#\ 421 "04299#\ 693b"6299# 101 "45199#\ 141b"20499#\ 299 "13299#\ 313 "04999#\ 579b "2699# ap!NO1 129 "091599#\ 181b"13199#\ 399 "02499#\ 437 "7499#\ 639b"3299# 101 "51699#\ 137 "32399#\ 185 "25499#\ 339b"06099#\ 621b "2799# an!H 121 "82199#\ 293 "22999#\ 279 "11499#\ 445 "06199#\ 619b"6299# 105 "59999#\ 149b"26899#\ 299b"05699#\ 253 "05699#\ 359 "04399#\ 645b"0899# aIn acetonitrile solution[ bShoulder[
and Qf observed Coulomb countŁ\ a}ording yellowish!
brown solutions of ðRuIV"aeac#"L#
1Ł¦[ These solutions
show identical cyclic voltammograms as their respective precursors\ the only exception being the ruthenium"III#Ð ruthenium"IV# couple appears as a reductive response[ The same oxidations were achieved chemically by a solu! tion of Ce3¦
in 0 M HClO3[ Electronic spectra of the
ðRuIV
"acac#"L#1Ł ¦
complexes in acetonitrile solution show several intense absorptions in the visible and UV region "Table 5\ Fig[ 1#[ Chemical or electrochemical reduction of the oxidized complexes gives the ðRuIII
"acac#"L#1Ł com!
plexes\ identi_ed by their characteristic electronic spectra[ Coulometric reduction of the ðRuIII
"acac#"L#1Ł com!
plexes near −9[5 V vs SCE quantitatively "n½0# a}orded
pink "blue for L an!H# solutions of ðRuII
"acac#"L#1Ł−[ The reduced solutions show identical cyclic
voltammograms ðbesides that the ruthenium"III#Ð ruthenium"II# couple appears as an oxidative responseŁ as their respective precursors[ The same pink "or blue#
solutions were also generated by chemical reduction of ðRuIII"acac#"L#
1Ł with hydrazine[ Electronic spectra of the
bivalent complexes\ recorded in acetonitrile solution\ show intense transitions in the visible and UV region "Table 5\ Fig[ 1#[ Coulometric or chemical "by hydrogen peroxide# oxidation of the pink "or blue# solutions gives back original solutions of the respective ðRuIII
"acac#"L#1Ł
complexes[ The above interconversions indicate that both the ruthenium"III#Ðruthenium"IV# and ruthenium"III#Ð ruthenium"II# couples are chemically reversible[
Addition of excess hydrazine to ðRuIII
"acac#"L#1Ł\
though initially causes instantaneous reduction to ðRuII
"acac#"L#1Ł −
\ slowly brings about a secondary chemical transformation producing deep pink solutions which show an intense absorption near 429 nm "e½49\999 M−0
cm−0#[ Though the exact composition of these species is
not clear yet\ it appears that the coordinated acac has underwent Schi}!base condensation with hydrazine yielding stable complexes of bivalent ruthenium[ Further
Fig[ 4[ Least!squares plot of E0:1values of "a# RuII:RuIIIcouple vs 1s and "b# RuIII:RuIVcouple vs 1s[
characterization of these species is currently under progress[
4[ Conclusions
This study shows that in spite of coordination by two azo nitrogens\ coordination by phenolate oxygen is more e}ective in stabilising higher oxidation states of ruthenium[ The possibility of using the ðRu"D1#"L#1Ł com!
plexes as starting materials for the synthesis of complexes of type ðRu"D1#"L#1Ł\ where D1is either a bidentate ligand
or two monodentate ligands\ is under scrutiny[ Template Schi} base condensation at the coordinated acetyl! acetonate ligand is also under investigation[
Acknowledgements
Financial support from the Council of Scienti_c and Industrial Research\ New Delhi ð90"0397#:85:EMR!IIŁ\ India\ is gratefully acknowledged[ Our sincere thanks go to Professor Animesh Chakravorty "Indian Association for the Cultivation of Science\ Calcutta#\ Professor Guru! nath Mukherjee "Calcutta University# and Dr[ Rup! endranath Banerjee "Jadavpur University# for their kind help[
References
ð0Ł "a# Hage R[ Coord Chem Rev 0880^000]050^ "b# Wallendael SV\ Rillema DP[ Coord Chem Rev 0880^000]186^ "c# Lever ABP\ Mausi
H\ Matealfc RA\ Stufkens DJ\ Dodsworth ES\ Auburn PR[ Coord Chem Rev 0882^014]206^ "d# Wong WT[ Coord Chem Rev 0883^020]34^ "e# Haga M\ Ali Md M\ Maegawa M\ Nozaki K\ Yoshimura A\ Ohno T[ Coord Chem Rev 0883^021]88^ "f # Con! stable EC\ Housecroft CE[ Coord Chem Rev 0883^023"Part 1#]022^ "g# Chan S\ Wong WT[ Coord Chem Rev 0884^027]108^ "h# Rich! mond MG[ Coord Chem Rev 0884^030]52^ "i# Chen L\ Poe AJ[ Coord Chem Rev 0884^032]154^ "j# Wong WY\ Wong WT[ Coord Chem Rev 0884^035"Part B#]296[
ð1Ł "a# Pramanik NC\ Bhattacharya S[ J Chem Res "S# 0886^87^ "b# Pramanik NC\ Bhattacharya S[ Trans Met Chem 0886^11]413^ "c# Basuli F\ Peng SM\ Bhattacharya S[ Inorg Chem 0886^25]4534^ "d# Pramanik NC\ Pramanik K\ Ghosh P\ Bhattacharya S[ Polyhedron 0887^06]0414[
ð2Ł "a# Krause RA\ Krause K[ Inorg Chem 0879^08]1599^ "b# Goswami S\ Chakravarty AR\ Chakravorty A[ Inorg Chem 0870^19]1135[ ð3Ł "a# Lahiri GK\ Bhattacharya S\ Ghosh BK\ Chakravorty A[ Inorg
Chem 0876^15]3213^ "b# Bag N\ Lahiri GK\ Bhattacharya S\ Fal! vello LR\ Chakravorty A[ Inorg Chem 0877^16]3285^ "c# Bhat! tacharya S\ Boone SR\ Fox GA\ Pierpont CG[ J Am Chem Soc 0889^001]0977^ "d# Bhattacharya S[ Polyhedron 0882^01]124^ "e# Bhattacharya S[ Polyhedron 0883^02]340^ "f# Chakravarty J\ Bbat! tacharya S[ Polyhedron 0885^04]146^ "g# Pramanik NC\ Bbat! tacharya S[ Polyhedron 0886^05]0644[
ð4Ł "a# Haendur HM\ Smith GMP[ J Am Chem Soc 0839^51]0558^ "b# Ueno K[ J Am Chem Soc 0846^68]2955^ "c# Jarvis\ JAJ[ Acta Cryst 0850^03]850^ "d# Price R[ J Am Chem Soc A 0858^0185^ "e# Kalia KC[ Indian J Chem 0869^7]0924^ "f# Dyachenko OA\ Atovmyan L\ Aldoshin SM[ Chem Soc Chem Commun 0864^ 094^ "g# Marov IN\ Gambarov DG\ Belyaeva VK\ Guseinov AG\ Sokolov AB[ Russ J Inorg Chem 0837^1809]0341^ "h# Sinha CR\ Bandopadhyay
D\ Chakravorty A[ J Chem Soc Chem Commun 0877\ 357^ "i# Bhawmik R\ Biswas H\ Bandopadhyay P[ J Org Met Chem 0884^70]387^ " j# Callis CF\ Nielsen NC\ Bailar Jr JC[ J Am Chem Soc 0841^63]2350[
ð5Ł Basuli F\ Peng SM\ Bhattacharya S[ Polyhedron 0887 Vol[ 06\ in press[
ð6Ł Lahiri GK\ Bhattacharya S\ Mukherjee S\ Mukherjee M\ Chak! ravorty A[ Inorg Chem 0876^15]2248[
ð7Ł Benson EP\ Legg JI[ Inorg Chem 0870^19]1493^ "b# Chakravarty J\ Bhattacharya S[ Polyhedron 04^0936^ "c# Sinha PK\ Chakravarty J\ Bhattacharya S[ Polyhedron 0885^04]1820^ "d# Pramanik NC\ Bhattacharya S[ Polyhedron 0886^05]2936[
ð8Ł Endo A\ Watanbe M\ Hayashi S\ Shimizu K\ Sato GP[ Bull Chem Soc Jpn 0867^40]799[
ð09Ł Bardwell DA\ Black D\ Je}ery JC\ Schatz E\ Ward MD[ J Chem Soc Dalton Trans 0882^1210[
ð00Ł Yamaguchi K\ Sawyer DT[ Inorg Chem 0874^13]860[ ð01Ł Seal A\ Roy S[ Acta Cryst C 0873^39]818[
ð02Ł Manivannan V\ Dirghangi BK\ Pal CK\ Chakravorty A[ Inorg Chem 0886^25]0415[
ð03Ł "a# Chao GKJ\ Sime RL\ Sime RJ[ Acta Cryst B 0862^18]1734^ "b# Hasegawa T\ Lau TC\ Taube H\ Schaefer WP[ Inorg Chem 0880^29]1810[
ð04Ł "a# Bleany B\ O|Brien\ MCM[ Proc Phys Soc London B 0845^58]0105^ "b# Gri.th JS[ The theory of transition metal ions[ London] Cambridge University Press\ 0850[ p[ 253[
ð05Ł Bhattacharya S\ Chakravorty A[ Proc Indian Acad Sci Chem Sci 0874^84]048[
ð06Ł Hammett LP[ Physical Organic Chemistry\ 1nd edn[ New York] McGraw Hill\ 0869[
ð07Ł Mukherjee RN\ Rajan OA\ Chakravorty A[ Inorg Chem 0871^10]674[
