Structures, electrochemical and spectroscopic properties of ternary ruthenium(II)-polypyridyl complexes with additional carboxylate, biguanide or sulfonamide donors

Article abstract of DOI:10.1016/S0277-5387(98)00145-4

The following complexes have been prepared: [Ru(bipy)₂(pic)][PF₆] (bipy=2,2′-bipyridine; Hpic= picolinic acid); [Ru(terpy)(dipic)] (terpy=2,2′:6′,2″-terpyridine; H₂dipic=dipicolinic acid); [Ru(bipy)₂ (Hbig)][PF₆]₂ (Hbig=biguanide); and [Ru(bipy)₂(apps)][PF₆] [where Happs is the p-tolylsulfonamide of 2-(2-aminophenyl)-pyridine]. The latter three have been characterised by X-ray crystallography and are all mononuclear pseudo-octachedral complexes. Electrochemical studies reveal the relationship between the potential of the metal-based Ru(II)Ru(III) couple, with the potential values being clearly related to the σ-donor or π-acceptor capabilities of the ligands. The energies of the lowest-energy m.l.c.t. maxima in the electronic spectra also correlate with ligand properties. [Ru(bipy)₂(Hbig)][PF₆]₂, which has a dissociable proton on the biguanide ligand, undergoes deprotonation in strongly basic conditions (pK_a=12.3±0.2), which results in a red-shift of the m.l.c.t. transition consistent with weakening of the ligand field due to the increased π-donor capability of the deprotonated ligand.

Full text of DOI:10.1016/S0277-5387(98)00145-4

Polyhedron Vol[ 06\ No[ 19\ pp[ 2430Ð2449\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166!4276"87#99034!3
Structures\ electrochemical and spectroscopic
properties of ternary ruthenium"II#!polypyridyl
complexes with additional carboxylate\
biguanide or sulfonamide donors
Samantha M[ Couchman\ Jose M[ Dominguez!Vera\ John C[ Je}ery\
ꢀ
Colin A[ McKee\ Simon Nevitt\ Matthias Pohlman\ Claire M[ White
and Michael D[ Wardꢁ
School of Chemistry\ University of Bristol\ Cantock|s Close^ Bristol\ BS7 0TS\ U[K[
"Received 05 February 0887^ accepted 06 April 0887#
Abstract*The following complexes have been prepared] ðRu"bipy#1"pic#ŁðPF5Ł "bipyꢂ1\1?!bipyridine^ Hpicꢂ
picolinic acid#^ ðRu"terpy#"dipic#Ł "terpyꢂ1\1?]5?\1ý!terpyridine^ H1dipicꢂdipicolinic acid#^ ðRu"bipy#1
"Hbig#ŁðPF5Ł1 "Hbigꢂbiguanide#^ and ðRu"bipy#1"apps#ŁðPF5Ł ðwhere Happs is the p!tolylsulfonamide of 1!
"1!aminophenyl#!pyridineŁ[ The latter three have been characterised by X!ray crystallography and are all
mononuclear pseudo!octachedral complexes[ Electrochemical studies reveal the relationship between the poten!
tial of the metal!based Ru"II#:Ru"III# couple\ with the potential values being clearly related to the s!donor or
p!acceptor capabilities of the ligands[ The energies of the lowest!energy m[l[c[t[ maxima in the electronic spectra
also correlate with ligand properties[ ðRu"bipy#1"Hbig#ŁðPF5Ł1\ which has a dissociable proton on the biguanide
ligand\ undergoes deprotonation in strongly basic conditions "pKaꢂ01[229[1#\ which results in a red!shift of
the m[l[c[t[ transition consistent with weakening of the ligand _eld due to the increased p!donor capability of
the deprotonated ligand[ Þ 0887 Elsevier Science Ltd[ All rights reserved
Keywords] ruthenium complexes^ electrochemistry^ crystal structures[
———————————————————————————————————————————————
INTRODUCTION
can be prepared by controllable stepwise methods\
all make ruthenium complexes particularly attractive
targets of study[
We ð0Ð2Ł and others ð3\ 4Ł have been interested in
studying the properties of ruthenium complexes with
a variety of ligand donor sets[ One impetus for this is
the particularly clear correlations which can be
observed between electrochemical properties and
ligand donor set ð0\ 3Ł[ Another is the widespread use
of redox!active ruthenium fragments as components
of polynuclear complexes linked by conjugated bridg!
ing ligands\ in which inter!valence charge transfer is
studied as a model for electron transport in molecular
wires ð5Ł[ The kinetic stability of ruthenium in several
di}erent oxidation states "particularly ¦1 and ¦2#\
the often reversible nature of the ¦1:¦2 couple\ and
the relative ease with which mixed!ligand complexes
We describe here the syntheses and the electro!
chemical and electronic spectroscopic properties of
four mononuclear complexes of ruthenium"II# with
mixed donor sets[ These complexes are ðRu"bipy#1
"pic#ŁðPF5Ł "bipyꢂ1\1?!bipyridine^ Hpicꢂpyridine!1!
carboxylic acid\ also known as picolinic acid#^ ðRu
"terpy#"dipic#Ł "terpyꢂ1\1?]5?\1ý!terpyridine^ H1dipicꢂ
pyridine!1\5!dicarboxylic acid\ also known as dipi!
colinic acid#^ ðRu"bipy#1"Hbig#ŁðPF5Ł1 "Hbigꢂ
biguanide#^ and ðRu"bipy#1"apps#ŁðPF5Ł ðwhere Happs
is the p!tolylsulfonamide of 1!"1!aminophenyl#
pyridineŁ[ The ligands are shown below^ the latter
three complexes have been crystallographically
characterised[ The complexes ðRu"bipy#1"pic#ŁðPF5Ł ð6\
7Ł and ðRu"terpy#"dipic#Ł ð8Ł were both reported very
recently while this work was in progress but have not
been directly compared[
ꢁ Author to whom correspondence should be addressed[
2430

2431
S[M[ Couchman et al[
EXPERIMENTAL
quality crystals[ Found] C\ 22[7^ H\ 2[9^ N\ 05[4)[
Required for C11H12F01N8P1Ru = MeCN] C\ 23[0^ H\
2[0^ N\ 05[5)[ Electrospray MS] m:z 402 ð49)\
General details
0
"Ru"bipy#1"big##¦Ł[ H NMR "299 MHz\ CD2CN#] d
ðRu"bipy#1Cl1Ł = 1H1O ð09Ł\ ðRu"terpy#Cl2Ł ð00Ł\ 7[81 "1 H\ d\ J 4[4#\ 7[32 "1 H\ d\ J 6[8#\ 7[23 "1 H\ d\ J
biguanide ð01Ł\ Happs ð02Ł and ðRu"bipy#1"pic#ŁðPF5Ł 6[8#\ 7[97 "1 H\ td\ J 6[8\ 0[4#\ 6[72 "1 H\ td\ J 6[8\ 0[4#\
ð6\ 7Ł were prepared according to the published pro! 6[55 "3 H\ m#\ 6[06 "1 H\ ddd\ J 6[4\ 4[6\ 0[2 Hz#\ 4[53
cedures[ Dipicolinic acid was obtained from Aldrich "ca[ 0 H\ br s\ NH#\ 4[91 "ca[ 1 H\ br s\ NH#[
and used as received[ Instrumentation used for routine
ðRu"bipy#1"apps#ŁðPF5Ł[ A solution of ðRu"bipy#1
spectroscopic and electrochemical analyses has been "H1O#1Ł1¦ "9[05 mmol# was generated by reaction of
described in earlier papers ð0\ 1Ł[
ðRu"bipy#1Cl1Ł = 1H1O "73 mg\ 9[05 mmol# with AgNO2
"1 equiv[# in EtOH:H1O "0]0\ 29 cm2# at re~ux for
0 hour\ followed by removal of the AgCl by _ltration[
To this was added Happs "49 mg\ 9[05 mmol# and the
mixture was re~uxed with stirring for a further 0 h[
Addition of aqueous KPF5 precipitated a solid which
was collected by _ltration and dried[ The crude pro!
duct was puri_ed by chromatography on silica with
MeCN:H1O:saturated aqueous KNO2 "03]1]0# as
eluent[ The main deep red:purple band was collected\
the solution concentrated in vacuo\ and the product
precipitated by addition of aqueous KPF5[ Filtration
and drying in vacuo a}orded pure ðRu"bipy#1"apps#Ł
ðPF5Ł in 69) yield[ Recrystallisation from CH1CI1:
hexane a}orded X!ray quality crystals[ Found] C\ 38[9^
H\ 2[3^ N\ 7[2)[ Required for C27H20F5N5O1PRuS =
CH1Cl1] C\ 37[4^ H\ 2[3^ N\ 7[6)[ FAB MS] m:z 626
ð79)\ "Ru"bipy#1"apps##¦Ł[
Preparations
ðRu"terpy#"dipic#Ł[ A mixture of dipicolinic acid
"04[1 mg\ 9[98 mmol# and Na1CO2 "19 mg\ 9[07 mmol#
was dissolved in water and heated to re~ux[ ðRu
"terpy#Cl2Ł "39 mg\ 9[98 mmol# was then added and the
mixture heated to re~ux for a further 4 hours\ during
which time a purple solid precipitated and the super!
natant solution became green[ The solid was _ltered
o}\ washed with water\ and air!dried to give ðRu"terpy#
"dipic#Ł in 54) yield[ X!ray quality crystals were
grown by di}usion of diethyl ether vapour into a
saturated solution of the complex in dmf[ Found] C\
38[9^ H\ 2[4^ N\ 09[3)[ Required for C11H03N3O3Ru =
H1O] C\ 38[2^ H\ 2[3^ N\ 09[4)[ The complex is not
su.ciently volatile to give a good mass spectrum[
ðRu"bipy#1"Hbi`#ŁðPF5Ł1[
A
mixture of ðRu
"bipy#1Cl1Ł = 1H1O "9[029 g\ 9[14 mmol# and Hbig X!ray crystallo`raphy
"9[918 g\ 9[18 mml# in dry ethanol "04 cm2# was heated
to re~ux under N1 for 3 hours to give a purple solution[
Suitable crystals were quickly transferred from the
After cooling\ aqueous KPF5 was added and the mix! mother liquor to a stream of cold N1 at −099>C on a
ture was concentrated in vacuo until a purple pre! Siemens SMART di}ractometer _tted with a CCD!
cipitate appeared[ This was collected by _ltration and type area detector[ In all cases data were collected at
dried to give ðRu"bipy#1"Hbig#ŁðPF5Ł1 in 79) yield[ −099>C to a 1u limit of 44> using graphite!mono!
Recystallisation from MeCN:ether a}orded X!ray chromatised MoÐKa radiation[ A detailed experi!

Structures\ electrochemical and spectroscopic properties of ternary ruthenium"II#!polypyridyl complexes 2432
mental description of the methods used for data col! molecule lies on a C1 axis which passes through C"13#\
lection and integration using the SMART system has N"10#\ Ru"0#\ N"20# and C"23#^ there are therefore 05
been published ð03Ł[ Table 0 contains a summary of complete molecules in the Fddd unit cell which has
the crystal parameters\ data collection and re_nement[ 21 general positions[ Each asymmetric unit contained
Empirical absorption corrections were applied to the one half of the complex molecule\ one half of a water
datasets using SADABS ð04Ł[ The structures were molecule "the oxygen atom also being on a special
solved by conventional heavy!atom or direct methods position#\ and a badly disordered solvent molecule
and re_ned by the full!matrix least!squares method around the intersection of two C1 axes[ This could
on all F1 data using the SHELXTL 4[92 package on only be modelled by putting carbon atoms at the sites
a Silicon Graphics Indy computer ð05Ł[ Non!hydrogen of maximum electron density and allowing the site
atoms were re_ned with anisotropic thermal par! occupancies to re_ne[ The result was approximately
ameters^ hydrogen atoms were included in calculated 1[4 atoms\ which we assume corresponds to half a
positions and re_ned with isotropic thermal par! disordered ether molecule in the asymmetric unit per
ameters riding on those of the parent atom[ The struc! half complex molecule and half solvent molecule\ i[e[
tural determinations of ðRu"bipy#1"Hbig#ŁðPF5Ł1 = ðRu"terpy#"dipic#Ł = H1O = Et1O[ Hydrogen atoms were
MeCN and ðRu"bipy#1"apps#ŁðPF5Ł = CH1Cl1 were not included in the re_nement for the disordered
straightforward and presented no particular prob! solvent molecule[
lems^ the only point to note is that in ðRu"bipy#1
"Hbig#ŁðPF5Ł1 = MeCN the asymmetric unit contains
two crystallographically independent molecules of the
complex and two molecules of MeCN[
RESULTS AND DISCUSSION
Crystals of ðRu"terpy#"dipic#Ł = H1O = Et1O were very
thin plates "those used had a thickness of 9[91 mm#
and therefore di}racted rather weakly[ Only data to a
Synthesis of and crystal structure of ðRu"terpy#"dipic#Ł
Preparation and puri_cation of this complex was
1u limit of 49> was used in the _nal re_nement\ as no straightforward and it was isolated cleanly in good
signi_cant di}racted intensity was observed between yield[ It is only very sparingly soluble in dmf and
49> and 44>\ and inclusion of the higher!angle data dmso\ and insoluble in other solvents\ so a good mass
only increased the R indices with no concomitant spectrum could not be obtained[ Attempts to obtain
improvement in the precision of the structure[ The NMR spectra were likewise unsuccessful\ due to a
Table 0[ Crystallographic data for the new complexes
Compound
ðRu"terpy#"dipic#Ł = H1O = Et1O
ðRu"bipy#1"Hbig#ŁðPF5Ł1 =
MeCN
ðRu"bipy#1"apps#ŁðPF5Ł =
CH1Cl1
Formula
M
C15H15N3O5Ru
480[47
Orthorhombic\ Fddd
7[635"1#
08[786"3#
42[803"01#
89
89
89
8271"3#
05
0[564
C13H15F01N09P1Ru
734[45
Triclinic\ P 0
C28H22Cl1F5N5O1PRuS
855[60
¹
System\ space group
Monoclinic\ P10:c
7[7704"8#
08[892"1#
11[746"4#
89
83[16"1#
89
3918[2"09#
3
Ä
a:A
00[3289"02#
03[437"1#
08[601"1#
79[587"8#
65[690"6#
77[063"7#
2049[2"5#
3
b:Aý
c:Aý
a:>
b:>
g:>
U:Aý2
Z
Dc` cm−2
0[672
9[696
0[483
9[574
m:mm−0
9[610
F"999#
3721
0577
0841
Crystal size:mm
Re~ections collected]
total\ independent\ Rint
1u limits for data\>
Data\ restraints\ parameters
9[49×9[49×9[91
07649\ 1965\ 9[9709
9[3×9[2×9[0
21247\ 03085\ 9[9167
9[4×9[1×9[0
14498\ 8113\ 9[9335
2Ð49
2Ð44
2Ð44
1960\ 9\ 073
9[9437\ 9[0364
9[9775\ 1[9073
¦0[461\ −0[070
03085\ 9\ 774
9[9231\ 9[9896
9[9386\ 9
8113\ 9\ 423
9[9396\ 9[0990
9[9348\ 9[8365
¦9[699\ −9[752
a\b
Final R0\ wR1
Weighting factors "a\b#b
−2
Ä
Largest peak\ hole :e A
¦0[006\ −9[576
aStructure was re_ned on F91 using all data^ the value of R0 is given for comparison with older re_nements based on Fo
with a typical threshold of Fꢀ3s"F#[
b wR1ꢀðSðw"F19−F1c #1Ł:Sw"F91#1Ł0:1 where w−0ꢀðs1"F19#¦"aP#1¦bPŁ and Pꢀðmax"F91\9#¦1F1c Ł:2[

2433
S[M[ Couchman et al[
combination of poor solubility and the ease with Synthesis and crystal structure of ðRu"bipy#1
which it oxidises in solution to the paramagnetic "Hbi`#ŁðPF5Ł1
Ru"III# state "see below#[ However the elemental
analysis and crystal structure "below# provide unam!
biguous characterisation[
Although complexes of _rst!row transition metal
ions with biguanide have been known for a long time
ðRu"terpy#"dipic#Ł "Fig[ 0\ Table 1# has the expected ð07Ð13Ł\ there are no reports of any complexes with
pseudo!octahedral structure\ with a trans!N3O1 donor ruthenium[ As a bidentate ligand with two unsatu!
set[ The terpy ligand shows the usual pattern of RuÐ rated "formally sp1!hybridised# N!donors there is an
N bond lengths\ with a short bond to the central obvious similarity with other diimines such as 1\1?!
Ä
atom ðRu"0#ÐN"10#\ 0[853"4# AŁ and longer ones to bipyridine "bipy#[ A notable property of biguanide is
the terminal two atoms ðRu"0#ÐN"00#:N"00A#\ that it can coordinate in either the neutral form "Hbig#
1[959"4# AŁ\ which arise from the steric limitations of or in the deprotonated form ðbigŁ− with a delocalised
Ä
the terpyridyl ligand ð06Ł[ The dipicolinate ligand structure reminiscent of the acetylacetonate anion
behaves similarly for the same steric reasons\ with the ð07Ł\ and crystal structures of both types of complex
two RuÐO bonds being signi_cantly longer than the are known[
four RuÐN bonds\ and the localisation of single and
Reaction of ðRu"bipy#1Cl1Ł with Hbig in re~uxing
double CÐO bond character being apparent in the ethanol\ followed by precipitation of the complex as
two carboxylate fragments ð6\ 7Ł[ The presence of two its hexa~uorophosphate salt and recrystallisation\
anionic s!donor ligands on the same axis trans to one a}orded in high yield a material whose elemental
another has not resulted in any signi_cant lengthening analysis was consistent with the formulation ðRu
of the RuÐO bonds compared to those complexes with "bipy#1"Hbig#ŁðPF5Ł1[ This implies that the biguanide
N4O donor sets where a carboxylate donor is trans ligand is neutral\ rather than coordinating in the
to a pyridyl ring\ as in ðRu"bipy#1"pic#ŁðPF5Ł ð7Ł and anionic deprotonated form which would have given
ðRu"bpy!CO1#1Ł "where bpy!CO1H is 1\1?!bipyridine! ðRu"bipy#1"big#ŁðPF5Ł with only one hexa~uoro!
5!carboxylic acid# ð6Ł[ The non!coordinated oxygen phosphate anion and a substantially di}erent elemen!
atom O"25# is hydrogen!bonded to the lattice water tal analysis[ The ES mass spectrum con_rmed the
molecule\ with the non!bonded O"25# = = = O"water# presence of the expected complex cation\ and the
Ä
separation being 1[80 A\ typical of OÐH = = = O hydro! structure was _nally con_rmed by X!ray crystallo!
gen!bonding[ graphy "Figure 1\ Table 1#[
Fig[ 0[ Crystal structure of ðRu"terpy#"dipic#Ł[

Structures\ electrochemical and spectroscopic properties of ternary ruthenium"II#!polypyridyl complexes 2434
Table 1[ Selected bond lengths "Aý# and angles "># for the three crystal structures
ðRu"terpy#"dipic#Ł = H1O = 9[4Et1O
ðRu"bipy#1"Hbig#ðPF5Ł1 = MeCN
ðRu"bipy#1"apps#ðPF5Ł = CH1Cl1
RuÐN"10#
RuÐN"20#
RuÐN"00A#
RuÐN"00#
RuÐO"26A#
RuÐO"26#
0[853"4#
0[868"5#
1[959"4#
1[959"4#
1[000"2#
1[000"2#
RuÐN"000#
RuÐN"030#
RuÐN"010#
RuÐN"020#
RuÐN"045#
RuÐN"040#
1[935"1#
1[935"1#
1[949"1#
1[952"1#
1[956"1#
1[969"1#
RuÐN"10#
RuÐN"20#
RuÐN"00#
RuÐN"30#
RuÐN"40#
RuÐN"59#
1[947"2#
1[959"1#
1[950"2#
1[952"1#
1[988"2#
1[030"2#
N"10#ÐRuÐN"20#
079[9
N"000#ÐRuÐN"030#
N"000#ÐRuÐN"010#
N"030#ÐRuÐN"010#
N"000#ÐRuÐN"020#
N"030#ÐRuÐN"020#
N"010#ÐRuÐN"020#
N"000#ÐRuÐN"045#
N"030#ÐRuÐN"045#
N"010#ÐRuÐN"045#
N"020#ÐRuÐN"045#
N"000#ÐRuÐN"040#
N"030#ÐRuÐN"040#
N"010#ÐRuÐN"040#
N"020#ÐRuÐN"040#
N"045#ÐRuÐN"040#
89[51"7#
67[83"8#
85[47"8#
85[16"7#
67[73"8#
062[30"8#
062[45"8#
81[37"7#
84[98"7#
78[76"7#
80[39"7#
063[98"8#
78[15"8#
84[31"8#
75[96"8#
N"10#ÐRuÐN"20#
N"10#ÐRuÐN"00#
N"20#ÐRuÐN"00#
N"10#ÐRuÐN"30#
N"20#ÐRuÐN"30#
N"00#ÐRuÐN"30#
N"10#ÐRuÐN"40#
N"20#ÐRuÐN"40#
N"00#ÐRuÐN"40#
N"30#ÐRuÐN"40#
N"10#ÐRuÐN"59#
N"20#ÐRuÐN"59#
N"00#ÐRuÐN"59#
N"30#ÐRuÐN"59#
N"40#ÐRuÐN"59#
71[33"09#
67[75"09#
N"10#ÐRuÐN"00A#
N"20#ÐRuÐN"00A#
N"10#ÐRuÐN"00#
N"20#ÐRuÐN"00#
N"00A#ÐRuÐN"00#
N"10#ÐRuÐO"26A#
N"20#ÐRuÐO"26A#
N"00A#ÐRuÐO"26A#
N"00#ÐRuÐO"26A#
N"10#ÐRuÐO"26#
N"20#ÐRuÐO"26#
N"00A#ÐRuÐO"26#
N"00#ÐRuÐO"26#
O"26A#ÐRuÐO"26#
68[50"01#
099[28"01#
68[59"01#
099[39"01#
048[1"1#
090[18"8#
67[60"8#
77[6"1#
099[09"09#
83[52"09#
67[46"09#
062[37"09#
099[15"09#
064[91"09#
73[47"09#
85[86"09#
061[38"8#
82[85"8#
84[3"1#
090[18"8#
67[60"8#
84[3"1#
77[6"1#
046[3"1#
84[26"09#
80[98"8#
72[72"09#
atoms are very similar to the other two[ The RuÐ
N"biguanide# distances are consistent with the N
atoms being sp1!hybridised[ Two geometric features
of the coordinated biguanide ligands are worth a com!
ment[ Firstly\ the angle at the central N atom\ C"044#Ð
N"043#ÐC"041#\ is 018[9"1#> ð018[0"2#> at N"143# in the
independent complex dicationŁ[ This is consistent with
the ligand being in the neutral Hbig form\ with steric
repulsion between the two bulky arms attached to the
central N atom resulting in the CÐNÐC angles being
considerably {{opened out||^ ð19\ 10Ł when the ligand
is deprotonated\ the increased delocalisation through!
out the chelate ring results in these CÐNÐC angles
being much closer to the ideal 019> ð19\ 11\ 13Ł[
Secondly\ the Ru atom is not quite in the same plane
as the "near!planar# biguanide ligand^ the angle
between the mean plane of the _ve ligand atoms in
the chelate ring ðN"040#\ C"041#\ N"043#\ C"044#\
N"045#Ł and the RuN1 coordination plane ðRu"0#\
N"040#\ N"045#Ł is 5[8> in the cation depicted "8[1> for
the independent complex dication#[ This is again a
common\ but not consistent\ feature of biguanide
complexes ð19\ 10Ł[
Fig[ 1[ Crystal structure of the cation of ðRu"bipy#1
"Hbig#ŁðPF5Ł1[
The asymmetric unit contains two independent
0
The solution H NMR spectrum showed the pres!
ðRu"bipy#1"Hbig#ŁðPF5Ł1 = MeCN groups[ Figure
1
ence of the expected 7 aromatic proton environments
"relative intensity 1 H each# for the bipyridyl ligands\
which are equivalent but within which the two pyridyl
rings are inequivalent[ Two broad singlets at 4[91 and
shows one of the independent complex cations^ the
structure of the alternate one is very similar[ It has
the expected octahedral structure with unremarkable
bond lengths and angles in the coordination sphere[
There is no sign of any signi_cant trans e}ect\ as the 4[54 ppm we assign to NH protons\ but the integrals
RuÐN"pyridyl# bonds trans to the biguanide donor are rather low\ presumably due to exchange with pro!

2435
S[M[ Couchman et al[
Fig[ 2[ Crystal structure of the cation of ðRu"bipy#1"apps#ŁðPF5Ł[
tons in the moisture that is present in the solvent[ We despite the bulky and sterically hindering nature of the
would expect three di}erent NH proton environments p!tolyl!sulfonamide fragment[ There is an interaction
on the basis of the crystal structure\ so we assume that between O"0# of the sulfonamide group and one of the
Ä
the most acidic proton "the central NH# is in fast pyridyl rings\ with a distance of 2[00 A between O"0#
exchange with the H1O protons and the signal for this and the mean plane of this pyridyl ring[ This appears
is therefore invisible[
to lengthen the RuÐN bonds to the apps ligand\ as
RuÐN"40# is the longest of the RuÐN"pyridyl# bonds
Ä
at 1[988"2# A\ and the RuÐN"sulfonamide# distance
Synthesis and crystal structure of ðRu"bipy#1
"apps#ŁðPF5Ł[
Ä
ð1[030"2# AŁ is even longer[ This contrasts with the
four!coordinate\ relatively unhindered\ complexes of
the same ligand with Cu"II#\ Co"II# and Pd"II# in
which the metal!N"sulfonamide# bonds were shorter
than\ or about the same length as\ the metal!N
"pyridyl# bonds ð02Ł[
We recently reported the synthesis of Happs\ a bide!
natate chelating ligand with one pyridyl and one sul!
fonamide donor\ and the crystal structures of some of
its complexes ð02Ł[ The new complex ðRu"bipy#1"apps#Ł
ðPF5Ł\ with _ve pyridyl ligands and one anionic sul!
fonamide ligand\ was simply prepared by reaction of
Happs with the labile complex ðRu"bipy#1"H1O#Ł1¦
^
Electrochemical properties of ðRu"bipy#1"pic#ŁðPF5Ł and
we found that this gave a cleaner product than that ðRu"terpy#"dipic#Ł
obtained from the reaction of Happs directly with
ðRu"bipy#1Cl1Ł[ The elemental analysis and FAB mass
Cyclic voltammetry in dmf showed that ðRu"bipy#1
spectrum con_rmed the formulation of the complex[ "pic#ŁðPF5Ł has a reversible one!electron wave at
0
The H NMR spectrum in MeCN gave the correct ¦9[39 V vs[ the ferrocene:ferrocenium couple
ratio of integrals for the aromatic and aliphatic "Fc:Fc¦#\ corresponding to a metal!centred Ru"II#:
"methyl# protons\ but the 17 inequivalent aromatic Ru"III# couple\ and two reversible one!electron waves
protons occurred in an overlapping mass between at −0[76 and −1[01 V vs[ Fc:Fc¦\ corresponding to
5[4 amd 7[4 ppm which could not be individually ligand!centred processes "electrochemical data are
assigned[
collected in Table 2#[ By {{reversible|| is meant that the
The crystal structure "Figure 2\ Table 1# shows that waves were symmetric "equal cathodic and anodic
the usual octahedral structure has been adopted peak currents#\ with peak!peak separations in the

Structures\ electrochemical and spectroscopic properties of ternary ruthenium"II#!polypyridyl complexes 2436
Table 2[ Electronic spectral and electrochemical data for the complexes[ The maxima of the lowest!energy m[l[c[t[ transitions
are in bold type
Cyclic voltammetric data
Complex
lmax "nm# ð09−2e "dm2 mol−0 cm−0#Ł
ðE0:1 V vs[ Fc:Fc¦Ł
ðRu"bipy#1"pic#ŁðPF5Ł
ðRu"terpy#"dipic#Ł
ðRu"bipy#1"Hbig#ŁðPF5Ł1
ðRu"bipy#1"apps#ŁðPF5Ł
384 "03#\ 344 "sh#\ 258 "02#\ 184 "67#a
¦9[39
¦9[01
¦9[10c
¦9[19
−0[76\ −1[01a
559 "sh#\ 484 "sh#\ 421 "7[2#\ 282 "09[5#\ 212 "16#\ 168 "13#a
493 "3[8#\ 259 "5[9#\ 239 "5[9#\ 181 "39#\ 133 "14#b
459 "sh#\ 383 "2[4#\ 222 "5[5#\ 186 "17#a
−1[90a
−0[80c
aIn dmf^ bin H1O^ cin MeCN[
region of 59Ð099 mV\ at a range of scan rates[ These doubly negatively!charged dipicolinate ligand was not
results agree well with recently reported values of observed[
¦9[77\ −0[32 and −0[57 V vs[ SCE in acetonitrile
ð6Ł[
The relationship between Ru"II#:Ru"III# redox
potential and donor set in the series ðRu"bipy#2Ł1¦
\
The Ru"II#:Ru"III# couple of ðRu"bipy#2ŁðPF5Ł1 ðRu"bipy#1"pic#Ł¦ and ðRu"terpy#"dipic#Ł "with N5\
under the same conditions is ¦9[78 V vs[ Fc:Fc¦\ so N4O and trans!N3O1 donor sets respectively# is clearly
replacement of a neutral pyridyl ligand by an anionic not linear] the second substitution of pyridyl by car!
carboxylate therefore stabilises the Ru"III# state by boxylate has a much smaller e}ect than the _rst sub!
389 mV[ This may be compared with the 759 mV stitution[ In ðRu"terpy#"dipic#Ł the two carboxylates
stabilisation of the Ru"III# state which occurs on are trans to one another\ and each will repel the other
replacing a pyridyl residue of ðRu"bipy#2Ł1¦ with a electrostatically\ reducing their ability to donate elec!
phenolate group in ðRu"bipy#1"no#ŁðPF5Ł ðHno is 1!"1! tron density to the metal centre compared to the car!
hydroxyphenyl#pyridineŁ\ which also has a N4O donor boxylate donor of ðRu"bipy#1"pic#Ł¦ which is trans to
set containing one anionic oxygen donor ð0Ł[ The com! an electron!withdrawing pyridyl group "although this
parison of ðRu"bipy#1"pic#Ł¦ with ðRu"bipy#1"no#Ł¦ is not really detectable in the crystal structures\ as
allows us to cancel out the electrostatic part of the described above#[ Further support for this comes from
stabilisation of the Ru"III# state which arises just as a the observation that in ðRu"bpy!CO1#1Ł\ with a cis!
consequence of reducing the overall charge on the N3O1 donor set\ the shift in the potential of the Ru"II#:
complex from ¦1 to ¦0\ which will be common to Ru"III# couple is almost exactly double that found for
both complexes[ The fact that a phenolate donor ðRu"bipy#1"pic#ŁðPF5Ł\ since in this case both car!
results in a cathodic shift of the Ru"II#:Ru"III# couple boxylate donors are trans to pyridyl groups ð6Ł[
which is 269 mV larger than that caused by the car!
boxylate donor is an indication of the di}erent s!
donor:p!acceptor properties of the two groups[ Electrochemical properties of ðRu"bipy#1"hbi`#ŁðPF5Ł
Clearly carboxylate is a poorer net electron donor and ðRu"bipy#1"apps#ŁðPF5Ł
than phenolate\ because of the partial delocalisation
of the negative charge within the carboxylate group
Cyclic voltammetry of ðRu"bipy#1"Hbig#ŁðPF5Ł1 in
onto the non!coordinated oxygen atom[ The poten! MeCN using a glassy carbon working electrode gave
tials of the two one!electron bipy!based reductions a single reversible wave at ¦9[10 V vs[ Fc:Fc¦[ We
may be compared with ðRu"bipy#2Ł1¦\ whose _rst two ascribe this to the Ru"II#:Ru"III# couple[ Replacing
reductions occur at −0[61 and −0[81 V vs[ Fc:Fc¦[ one bipy ligand by Hbig therefore results in stabil!
The more negative potentials required to reduce the isation of the Ru"III# state by 579 mV\ indicating that
bipy ligands of ðRu"bipy#1"pic#Ł¦ re~ect the smaller the metal centre of ðRu"bipy#1"Hbig#ŁðPF5Ł1 is much
positive charge on the complex[
more electron rich than that of ðRu"bipy#2Ł1¦ because
Cyclic voltammetry of ðRu"terpy#"dipic#Ł in dmf of the poorer p!acceptor capability of Hbig compared
revealed reversible one!electron waves centred at to the highly delocalised bipy[ At high negative poten!
¦9[01 V and −1[90 V vs[ Fc:Fc¦[ The _rst of these tials only poorly!de_ned irreversible processes could
corresponds to the Ru"II#:Ru"III# couple\ which has be observed which were not examined further[ Use of
undergone an additional cathodic shift of 179 mV a Pt working electrode instead of glassy carbon
compared to ðRu"bipy#1"pic#ŁðPF5Ł "which in turn was resulted in a very asymmetric wave for the Ru"II#:
cathodically shifted by 389 mV from ðRu"bipy#2Ł1¦#[ Ru"III# couple because of absorption of the oxidised
The couple at −1[90 V vs[ Fc:Fc¦ we assign to species onto the electrode surface[
reduction of the terpy ligand^ a reduction of the
Cyclic voltammetry of ðRu"bipy#1"apps#ŁðPF5Ł at a

2437
S[M[ Couchman et al[
Fig[ 3[ Electronic spectra of ðRu"bipy#1"Hbig#Ł1¦ in water at pH 6 "solid line#\ and ðRu"bipy#1"big#Ł¦ in water at pH 02 "dotted
line#[
Pt!bead electrode in MeCN gave reversible waves cen! then 423 nm in the series ðRu"bipy#2ŁðPF5Ł1\ ðRu
tred at ¦9[19 V and −0[80 V vs[ Fc:Fc¦\ assignable to
"bipy#1"pic#ŁðPF5Ł and ðRu"terpy#"dipic#Ł[ All of the
Ru"II#:Ru"III# and bipy!centred couples respectively[
The stabilisation of the Ru"III# state by 589 mV com!
pared to ðRu"bipy#2Ł1¦ arises because apps is both a
better s!donor than bipy because of its negative
charge\ and a poorer electron!acceptor because it con!
tains only one pyridyl ring[ Interestingly\ the Ru"II#:
Ru"III# couple of ðRu"bipy#1"apps#ŁðPF5Ł is 199 mV
more cathodic than that of ðRu"bipy#1"pic#ŁðPF5Ł\ indi!
cating that the anionic sulfonamide group is a better
net electron donor to ruthenium than the anionic car!
boxylate group\ possibly because nitrogen is less elec!
tronegative than oxygen and therefore more
polarisable[
complexes have one or two near!UV transitions in
the 299Ð399 nm range\ and the usual intense ligand!
centred transitions in the higher!energy UV region[
A pH titration of the electronic spectrum of ðRu
"bipy#1"Hbig#ŁðPF5Ł1 was e}ected by dissolving it in
aqueous 9[0 M KCI acidi_ed to pH 0\ and slowly rais!
ing the pH to 02 by addition of very small portions of
solid KOH[ In the pH range 0 to 00 the spectrum was
invariant\ but in the pH range 00Ð02 the spectrum
changes signi_cantly\ which we ascribe to depro!
tonation of the central NH group of the coordinated
Hbig ligand to give ðRuII"bipy#1"big#Ł¦\ since ðRu
"bipy#2Ł1¦ undergoes no such pH!induced spectral
change[ The pair of transitions at 239 and 259 nm
become red!shifted to 237 and 273 nm\ and the lowest!
energy MLCT band at 493 nm is likewise red!shifted
to 422 nm "Figure 3#[ A graph of lmax"MLCT# vs[ pH
"Figure 4# indicates that the pK value is 01[2 "29[1#\
and the same pK value could be obtained from plot!
ting other spectral parameters "e[`[ absorbance at
399 nm# as a function of pH[ The red!shift of the
m[l[c[t[ transitions indicates that on deprotonation the
metal d"p# orbitals are raised\ i[e[ ðbigŁ− is a weaker!
_eld ligand than Hbig^ that the bipy!based orbitals
are not signi_cantly perturbed is shown by the fact
that the two intense UV transitions are hardly a}ected
by deprotonation of the complex[ Deprotonation of
Hbig to ðbigŁ− results in formation of a negatively!
charged\ delocalised {{acac!like|| ligand ð08Ł which is
expected to be a better p!donor than neutral Hbig\
Electronic spectra of the complexes and pH titration of
ðRu"bipy#1"Hbi`#ŁðPF5Ł1
The electronic spectra of the complexes are sum!
marised in Table 2[ In all cases the lowest!energy
feature\ in the visible region\ may be ascribed to the
Ruðd"p#Ł:L"pꢁ# m[l[c[t[ process\ where L ꢂ bipy or
terpy as appropriate[ The red!shift of these compared
to the same transition in ðRu"bipy#2ŁðPF5Ł1 "ca[ 349 nm#
ð14Ł arises because of the weakening of the ligand _eld
by replacement of a strong!_eld pyridyl donors by
weaker!_eld carboxylate\ sulfonamide or biguanide
ligands\ which raises the d"p# levels[ The incremental
weakening of the ligand _eld on addition of one and
then two carboxylates to the donor set is apparent in
the shift of the m[l[c[t[ maximum from 349 to 384 and consistent with the above observation[

Structures\ electrochemical and spectroscopic properties of ternary ruthenium"II#!polypyridyl complexes 2438
Fig[ 4[ Wavelength of the m[l[c[t[ maximum of ðRu"bipy#1"Hbig#Ł1¦ as a function of pH[
Acknowled`ements*We thank the EPSRC for _nancial sup!
port[
S[\ Ghosh\ B[ K[ and Chakravorty\ A[\ Inor`[
Chem[\ 0876\ 15\ 3212^ "c# Constable\ E[ C[ and
Hannon\ M[ J[\ Inor`[ Chim[ Acta[\ 0882\ 100\
090^ "d# Pramanik\ R[ and Bhattacharya\ S[\ Poly!
hedron\ 0886\ 05\ 2936^ "e# Sinha\ P[ K[\ Chak!
ravarty\ J[ and Bhattacharya\ S[\ Polyhedron\
0886\ 05\ 70[
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