Ciencia  y  Tecnología,  27  (1  y  2):  60-­‐‑77,  2011  
ISSN:0378-­‐‑0524  
 
SYNTHESIS,  CHARACTERIZATION  AND  REDOX  BEHAVIOUR  OF  MIXED  
LIGAND  COPPER(II)  SACCHARINATE  COMPLEXES  
  
Grettel  Valle-­‐‑Bourrouet  1*,  Larry  R.  Falvello2  and  Julio  Gómez3  
  
1School  of  Chemistry,  University  of  Costa  Rica,  11501-­‐‑2060  San  Jose,  Costa  Rica.  
2  Department  of  Inorganic  Chemistry  and  I.C.M.A.,  University  of  Zaragoza-­‐‑CSIC,  Plaza  San  
Francisco  s/n,  E-­‐‑50009,  Zaragoza,  Spain.  
3  Department  of  Chemistry,  University  of  La  Rioja,  Complejo  Científico  Tecnológico,  Calle  Madre  
de  Dios  51,  26006  Logroño,  Spain.  
  
Recibido  21  de  julio,  2011;  aceptado  31  de  agosto,  2011  
  
  
Abstract  
Three   mixed-­‐‑ligand   complexes   of   Cu(II)   with   saccharin   (sac),   pyrazole,   (Hpz),  
imidazole,   (Himid)  were  synthesized  and  characterized  on   the  basis  of  elemental  
analysis,   FT-­‐‑IR   spectroscopy,   magnetic   susceptibility,   EPR   spectra,   and   X-­‐‑ray  
diffraction.   The   reaction   of   [Cu(sac)2(H2O)4]   ⋅   2H2O   with   pyrazol   in   methanol  
resulted  in  a  mononuclear  pentacoordinated  compound  [Cu(sac)2(Hpz)3]  (1)  and  a  
trinuclear  N,N.bridged  compound  [Cu3(sac)2(Hpz)3(pz)3)2(OH)]  (2),  forming  a  nine  
membered  [-­‐‑Cu-­‐‑N-­‐‑N-­‐‑]3  ring  and  µμ3-­‐‑OH  bridge;  each  Cu(II)  ion  is  tetracoordinated,  
with  weak   axial      interactions   from   saccharinate   ions.The  Himidazole   compound  
[Cu2(sac)4(Himid)4]   (3)   has   a   dinuclear   structure   with   two   saccharinate   ions   as  
bridge;  each  Cu(II)   ions  has  a  penta-­‐‑coordination  sphere,   two  N-­‐‑coordinated  and  
one  O-­‐‑coordinated   saccharinate   ions   on   the   equatorial   plane,   and   two   imidazole  
molecules  in  the  axial  positions.    
  
Resumen  
Se   sintetizaron   tres   complejos   de   cobre(II)   con   una  mezcla   de   ligandos,   sacarina  
(sac)   y   pirazol   (Hpz)   e   imidazole   (Himid).   Los   complejos   se   caracterizaron   por  
análisis  elemental,  espectroscopía  IR-­‐‑FT,  susceptibilidad  magnética,  esoectroscopia  
EPR  y  difracción  de  rayos  X.  La  reacción  de  [Cu(sac)2(H2O)4]  ⋅  2H2O  con  pirazol  en  
methanol  produce  un  compuesto  mononuclear  pentacoordinado,    [Cu(sac)2(Hpz)3]  
(1)    y  uno  trinuclear  [Cu3(sac)2(Hpz)3(pz)3)2(OH)]  (2),  con  puentes  N,N,  que  forman  
un  anillo  de  nueve  miembros  [-­‐‑Cu-­‐‑N-­‐‑N-­‐‑]3  y  un  puente  µμ3-­‐‑OH;  cada  átomo  de  cobre  
está   tetracoordinado   con   una   leve   interacción   axial   de   los   iones   sacarinato.      El  
compuesto  con  imidazol  [Cu2(sac)4(Himid)4]  (3)  posee  una  estructura  dinuclear  con  
dos   iones  sacarinato  puente,   cada  átomo  de  cobre  está  pentacoordinado,  con  dos  
                                            
*  Corresponding  author:  grettel.valle@ucr.ac.cr  
G.  VALLE-­‐‑BOURROUET  -­‐‑  L.R.  FALVELLO  -­‐‑  JULIO  GÓMEZ  
 
Ciencia  y  Tecnología,  27(1  y  2):  60-­‐‑77,  2011  –  ISSN:  0378-­‐‑0524  
 
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iones  sacarinatos  unidos  por  el  átomo  de  nitrógeno  y  uno  unido  por  un  átomo  de  
oxígeno  en  el  plano  equatorial  y  dos  moléculas  de  imidazol  en  la  posición  axial.  
  
Keywords:   Saccharinate   complexes,   hydrogen   bonds,   pyrazole,   imidazole,   metal  
complexes,  copper.  
  
Palabras   clave:   complejo   sacarinato,   enlaces   de   hidrógeno,   pirazol,   imidazole,   complejo  
metálico,  cobre.  
  
  
I   INTRODUCTION  
  
The  saccharinate  ion  has  been  shown  to  be  a  very  versatile  ligand,  since  it  offers  
different   donor   atoms   to  metal   centers,   namely  N,   O(carbonyl)   and   two  O   (sulfonyl)  
atoms.   In   certain   cases   it   acts   as   a   bridging   or   chelating   ligand,   through   its  N   and  O  
(carbonyl)  atoms  [1-­‐‑5],  (Scheme  1).  
N-
S
OO
O
N-
S
OO
O
M N
-
S
OO
O
M
N-
S
OO
O
M
N-
S
OO
O M
M
NH
S
OO
O
M
I II III
IV V VI   
Scheme  I:    Saccharinate  coordinations  modes.  
  
In  the  last  years,  there  has  been  reported  on  mixed  ligand  complexes  containing  
simultaneosly  saccharinate  and  some  other  ligands  in  the  coordination  sphere:  pyridine  
[6,7],   imidazole   [5],   2,2’bipyridine   [8].   These   ligands   can   produce   a   change   in   the  
coordination   mode   of   the   saccharinate   ligand.   In   the   complex   [V(sac)2(py)4]   [6]   it   is  
coordinate  through  an  O  (carbonyl)  atom,  with  imidazole  acting  as  bridging  ligand  [5].    
With   this   in   mind   we   have   attempted   to   prepare   similar   mixed-­‐‑ligand   complexes  
replacing  imidazole  by  pyrazole,  a  five  atoms  ring  molecule  like  imidazole,  to  carry  out  
the   reaction.   Furthermore,   pyrazole   is   an   interesting   ligand   able   to   provide   a   1,2-­‐‑
bridging   form   building  multinuclear   complexes[9].   The   reaction,   performed   in  water,  
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
Ciencia  y  Tecnología,  27(1  y  2):  60-­‐‑77,  2011  –  ISSN:  0378-­‐‑0524  62 
produced   complexes   of   formula   [M(sac)2(Hpz)2(H2O)2],   where   two   water   molecules  
were   substituted   by   pyrazole   molecules   [10]   and   also   [Cu(sac)2(Hpz)4],   where   the  
sacharinate  was  bound  to  metal  though  the  carbonyl  oxygen  atom[11].      
  
N
NH N NH
Hpz Himid
  
Scheme  II  
  
Here  we  report  the  products  of  the  reaction  of  copper  saccharinate  and  pyrazole  
and,  imidazole  (scheme  II)  in  methanol,  to  see  if  there  are  changes  in  the  coordinations  
sphere   of   the   saccharinate   complexes.   We   describe   here   the   crystal   structures,  
spectroscopic,  magnetic  and  electrochemical  properties  of  the  obtained  products.  
  
II   EXPERIMENTAL  
  
Methods   and   Materials:   Solvents,   pyrazole,   imidazole,   copper   nitrate,   and   sodium  
saccharinate   were   used   as   commercially   available   products.   The   complex  
[Cu(sac)2(H2O)4]·∙2H2O,   was   prepared   as   described   in   literature   [12]   and   isolated   as  
crystalline  material.    
  
Physico-­‐‑chemical  measurements:  FT-­‐‑IR  spectra  were  recorded  using  KBr  pellets  with  a  
Perkin   Elmer   Spectrum   100.   Cyclic   voltammperograms   were   performed   with   a  
computer  controlled  Autolab  PGSTAT  10,  in  a    nitrogen-­‐‑saturated  DMSO  solutions  with  
tetrabutilamonium   hexafluorophosphate   (TBAPF6,   0.1   mol/L)   as   a   supporting  
electrolyte,   glassy   carbon   electrode   as   working   electrode,   platinum   wire   as   counter  
electrode  and  Ag/AgCl    as  reference  electrode.  
X-­‐‑band  EPR  spectra  were  recorded  on  a  Bruker  ESP  300  spectrometer.  Simulation  
of  EPR  spectra  were  carried  out  using  ESIM  program.  [13a]    
  
Magnetic   susceptibility   data   were   measured   from   powder   samples   of   solid  
material  in  the  temperature  range  of  2-­‐‑300  K  by  using  a  SQUIT  susceptometer  MPMS-­‐‑7,  
Quantum   Design   with   a   field   of   1.0T.   The   experimental   data   were   corrected   for  
underlying   diamagnetism   by   the   use   of   tabulated   Pascal’s   constants.   Simulation   of  
magnetic  susceptibility  data  were  carried  out  using  the  JulX  program  (version  13).  [13b]  
Intermolecular   interactions   were   considered   by   using   a   Weiss   temperature,  ΘW,   as   a  
perturbation  of  the  temperature  scale,  kT’  =  k(T-­‐‑ΘW)  for  the  calculation.  
  
G.  VALLE-­‐‑BOURROUET  -­‐‑  L.R.  FALVELLO  -­‐‑  JULIO  GÓMEZ  
 
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X-­‐‑Ray  Crystallographic  Data  Collection  and  Refinement  of  the  Structure  
  
[Cu(C7H4NO3S)2(Hpz)3](1)    
  
A   regularly   shaped   blue   crystal   was   fixed   to   the   end   of   a   quartz   fiber   with   epoxy.  
Geometric  and  intensity  data  were  measured  using  a  CAD-­‐‑4  diffractometer.  Data  were  
reduced  using  the  program  XCAD4B  [25].  Absorption  corrections  were  based  on  eleven  
full  or  partial  ψ-­‐‑scans  of  reflections  with  Eulerian  equivalent  angle  χ  in  the  range  (-­‐‑36.0)  
–   (+62.0)°,   thus   achieving   as   broad   as   possible   a   dispersion   of   incident   and  diffracted  
beam  directions   [26].  The  structure  was   solved  by  direct  methods  and  refined  by   full-­‐‑
matrix  least-­‐‑squares.  Hydrogen  atoms  were  placed  at  calculated  positions  and  treated  as  
riding  atoms  in  the  refinement,  with  isotropic  displacement  parameters  set  to  1.2  times  
the  equivalent   isotropic  displacement  parameters  of  their  respective  parent  atoms.  The  
refinement  converged  with  the  residuals  given  in  Table  1.  The  polar  axis  direction  was  
established  by  refinement  of  the  absolute  structure  parameter  [27],  which  refined  stably  
to  a  value  of  0.00  (10).  
  
[Cu3(sac)2(Hpz)3(pz)3(OH)]·∙0.5(H2O)(2)  
  
A  blue  block-­‐‑like   crystal  was  mounted  at   the   end  of   a  quartz   fiber  using   epoxy.  Data  
were  collected  using  routine  procedures  on  a  KappaCCD  four-­‐‑circle  diffractometer  [28].  
Automated  structure  solution  was  carried  out  using  the  MAXUS  software  package  [29].  
The  final  development  and  refinement  of  the  structure  was  done  using  SHELXTL  [26].  
Two   partially   occupied   water   sites,   slightly   more   than   1   Å   apart,   were   located   and  
refined  anisotropically  with   a   common   set   of   anisotropic  displacement  parameters   for  
both,  and  with  one-­‐‑fourth  occupancy  each.  Their  hydrogen  atoms  were  not  located.  The  
hydroxy    hydrogen  atom  at  the  center  of  the  cluster  was  located  in  a  difference  map  and  
refined   as   a   riding   atom  with   its   isotropic   displacement   parameter   constrained   to   1.2  
times  the  equivalent  isotropic  displacement  parameter  of  the  carrier  O  atom.  All  of  the  
remaining  H  atoms  were  placed  at  calculated  positions  and  refined  as  riders  with  their  
U(iso)  constrained  to  1.2  U(eq)  of  their  parent  atoms.  Final  residuals  are  given  in  Table  1.  
Synthesis  
  
[Cu(C7H4NO3S)2(Hpz)3](1)  and  [Cu3(sac)2(Hpz)3(pz)3(OH)]·∙0.5(H2O)(2)  
  
[Cu(sac)2(H2O)4]·∙2  H2O  0.50  g  (1mmol)  and  pyrazole  0.30  g  (4.4  mmol)  were  mixed  in  50  
mL  methanol.  The  suspension  was  heated  for  1h,  and  formed  a  deep  blue  solution.  The  
solution,   after   standing   overnight,   yielded   0.3   g   of   bright   blue   prismatic   crystals   and  
0.01g  dark  blue  rectangular  crystals.  Both  crystals  obtained  in  this  way  were  suitable  for  
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
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X-­‐‑ray   analysis.      Anal:   Found   for   1:   C   43.66,   H   3.10,   N   17.75   S10.32.   Calc.   For  
CuC22H18N6O7S2  :  C43.65,  H  3.19,  N  17.71,  S  10.0  14.    Anal:  Found  for  2:  C  38.84,  H  3.11,  N  
19.90.  Calc.  For  Cu3C32  ,  H31N14  O8  S2  :  C  38.61,  H  3.11,  N  19.70.  λmax(εmol-­‐‑1  cm-­‐‑1):  645(81),  
µeff(for  1)=1.90  µμB,    µeff(for  2)=.1.92  µμB,  J=  -­‐‑211  cm-­‐‑1,  g  =  2.05  
  
  [Cu2(C7H4NO3S)4(imid)4](3)  
  
[Cu(sac)2(H2O)4]·∙2  H2O  0.53  g  (1mmol)  and  imidazole  0.30  g  (4.4  mmol)  were  mixed  in  30  
mL  ethanol.  The  suspension  was  heated  for  1h,  and  formed  a  sky  blue  solution  after  a  
few  minutes,  yielding  0.25  g  (50%),  of  a  brilliant  sky  blue  precipitated.  Suitable  crystals  
for  X  were  obtained  from  a  slow  evaporation  of  a  dmf  solution.    Anal:  Found:  C  43.66,  H  
3.10,  N  17.75  S10.32.  Calc.  For  CuC22H18N6O7S2:  C43.65,  H  3.19,  N  17.71,  S10.  14.     λmax(ε  
mol-­‐‑1cm-­‐‑1):  699(90),  µeff.  2,63  µμB.,  J=  -­‐‑2.24  cm-­‐‑1  ,  g  =  2.15.  
  
III   RESULTS  AND  DISCUSSION  
 
  Description   of   the   Crystal   Structures.      Thermal   ellipsoid   drawings   of   the   two  
structures,   indicating   the   atom   numbering   schemes,   are   depicted   in   figures   1   and   2.    
Bond   lengths   and   angles   are   given   in   table   2.   The   structure   of   1   consists   of   a  
mononuclear   compound,   with   a   non-­‐‑common   (in   the   case   of   cooper   saccharinate),  
pseudotrigonal   bipyramidal   coordination  geometry   around   the   central   ion  Cu2+.  Axial  
positions   are   occupied   by   two   nitrogen   atoms   of   pyrazole   molecules.   The   carbonyl  
group’s   oxygen   atom   of   one   saccharinate   ion,   the   nitrogen   atom   of   the   other  
saccharinate  ion  and  a  nitrogen  atom  of  the  pyrazole  molecule  build  the  trigonal  plane.  
The  orientation  of  each  of  the  pyrazole  rings  was  established  on  the  basis  of  hydrogen  
bonds   formed   by   the   respective  N-­‐‑H  moiety;   these   contacts   are   all   too   short   to   be  C-­‐‑
H...A   interactions,   N(1)-­‐‑N(4)   2.966   Å,   O(5).   There   are   some   examples   of   O-­‐‑bonded  
saccharinate   ions,   [V(sac)2(py)4]⋅2py]   [6a],   [Ni(sac)2(py)4]⋅2py   [6b],   [Cri(sac)2(py)3]   [6c],  
[Cu(dipyr)(N-­‐‑sac)(O-­‐‑sac)]   and   [Cu(sac)2(Hpz)4].   [11].   In   all   these   cases   the   ion   adopts  
this  coordination  position   in  spite  of   the  normally  preferred  N-­‐‑bonded,  because  of   the  
steric  hindrance  caused  by  other  molecules  around  the  metal  ion.      
It  can  be  seen  in  the  significant  different  bond  distances  and  angles  in  the  plane  of  the  
molecule  Cu-­‐‑Osac   2.115(9)  Å,  Cu-­‐‑Nsac   2.024(8)  Å   and  Cu-­‐‑Npz   1.986(9)  Å.,  O1-­‐‑Cu-­‐‑N3  
120.4°,  Ni-­‐‑Cu-­‐‑N3  140.4°  and  N2-­‐‑Cu-­‐‑O1    99.2°        The  Cu-­‐‑Osac  distance  in  [Cu(dipyr)(N-­‐‑
sac)(O-­‐‑sac)]   is  shorter  1.968(1)  Å  than  1,  while  Cu-­‐‑Nsac  is  practically  the  same  2.017(1)  
Å,  in  this  case  the  molecule  have  a  distorted  square  pyramidal  geometry,  with  the  two  
saccharinate  ions  in  the  plane  of  the  pyramid.  
Structure   2   consist   of   a   trinuclear   compound,   a   nine-­‐‑membered   [Cu-­‐‑N-­‐‑N]3  
metallcycle  where  each  Cu  atom  is  also  coordinated  to  a  pyrazole  molecule.  The  center  
of   this   cycle  accommodates   triply  bridging  hydroxy  molecule;   the   three  Cu-­‐‑-­‐‑-­‐‑O  bonds  
G.  VALLE-­‐‑BOURROUET  -­‐‑  L.R.  FALVELLO  -­‐‑  JULIO  GÓMEZ  
 
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lengths  are  very  similar,  Table  2.  Bond  angles  are  116.65  (8),  114.64  (8)  and  117.27(8).  The  
molecule  ring’s  Cu-­‐‑O  distances  and  Cu-­‐‑O-­‐‑Cu  angles  are  nearly  similar  to  rings  reported  
in  the  literature  for  the  core  [Cu3(µ3-­‐‑OH)(µ-­‐‑pz)3]  and  for  the  core  [Cu3(µ3-­‐‑O)  (µ-­‐‑pz)3]  [14,  
15a].     The  Cu(1)  atom   is   in  a  distorted  square  pyramidal  geometry,   intersecting   in   the  
apex  position  with   the  saccharinate   ion,     bound  to   the  saccharinate   ion  nitrogen  atom,  
N(13)  with  a  distance  of  2.343(2)  Å.  The  other  two  copper  ions  have  a  weak  interaction  
with   the   oxygen   atoms   from   the   SO2-­‐‑group,   Cu(2)-­‐‑O(3)   2.4981(18)   Å   and   Cu(3)-­‐‑O(4)  
2.5468(18)  Å.    A  second  saccharinate  molecule  lies  in  the  other  side  of  the  ring  plane  and  
interacts  with   the  copper   ions,  Cu(2)  and  Cu(3)  weaker   than   the   fist  one,   through  one  
sulphonyl  oxygen  atom,  Cu(3)-­‐‑O(7),  2.8307(19)  Å  and  the  carbonyl  oxygen,  Cu(2)-­‐‑O(5),  
2.7079(18)   Å.   These   two   interactions   build   a   very   elongated   pseudo-­‐‑octahedral  
environment  around  the  copper   ions.     The  compound  2   is  one  of   the  rare  examples  of  
symmetric   structure  core   [Cu3(µ3-­‐‑OH)(µ-­‐‑pz)3Hpz3]   [14].  Other  complexes  with   the  core  
[Cu3(µ-­‐‑OH)(µ-­‐‑pz)3]   are   known   [15],   such   as   the   series   [Cu3(µ3-­‐‑OH)(µ-­‐‑pz)3Cl3],   [Cu3(µ3-­‐‑
O)(µ-­‐‑pz)3Cl3],   [Cu3(µ-­‐‑Cl)2(µ-­‐‑pz)3Cl3]   [15a],   and   the   non   symmetric   structure   core   of  
[Cu3(µ3-­‐‑OH)(µ-­‐‑pz)3   (Hpz)2(NO3)2]   [15c].     The   structure  of   compound  3  was   identical   to  
the  published  by  Liu  et.  al.  [5]  
The   Cu-­‐‑Nsac   distance   is   comparable   with   the   corresponding   value   in   similar  
compounds,   Cu   (sac)2(py)2(H2O)   2.032(2)   Å   [16],   Cu   (sac)2(nic)2(H2O)   (nic   =   nicotinic  
acid)   2.044(7)   and   1.986(6)   Å   [11]   and  Cu   (sac)2(4-­‐‑propylpy)2(H2O)   2,021(4)   c   [17]   and  
shorter   than   one   found   in   Cu(sac)2(H2O)4·∙2H2O   2.061(2)   [1].   The   thiazole   molecule   is  
almost   perpendicular   to   the   plane   of   the   saccharinato   ligand.   The   angle   between   the  
corresponding   best   planes   is   88.4°.   The   compound   is   further   stabilized   by   relatively  
strong  intermolecular  hydrogen  bonds.  The  water  molecule  is  hydrogen  bonded  to  two  
saccharinato  carbonyl  oxygen  atoms  forming  an  infinite  chain  of  hydrogen  bonds  along  
the  z  axis.  The  O(16)·∙·∙·∙O(17)  distance  is  2.671(8)  Å.  
The  C-­‐‑O  bonds  in  the  three  molecules  lie  around  the  average  C-­‐‑O  distance  1.231  
Å  found  for  many  saccharinate  complexes  [18].    
  
  
  
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
Ciencia  y  Tecnología,  27(1  y  2):  60-­‐‑77,  2011  –  ISSN:  0378-­‐‑0524  66 
  
Figure  1:  Drawing  of  the  compound  1  showing  50%  probability  displacement  ellipsoids  
  
Table  1:  Crystal  data  and  structure  refinement  for  Cu(sac)2(Hpz)3  and    
[Cu3(sac)2(Hpz)3(pz)3)2(OH)]  
  
Empirical  formula   C23H20CuN8O6S2   C32H31Cu3N14O8S2  
Formula  weight   632,13   994.45  
Temperature   298(2)  K   123(2)  K  
Wavelength   0,71073  Å   0,71070  Å  
Crystal  system   Ortorrombic   Monoclinic  
Space  group   Pn  a  2(1)   P21/n  
Unit  cell  dimensions   a  =  14,3522(9)  Å          α   =  90°  
b  =  13,7018(11)  Å        β   =  90  °  
c=  13,4286  (18)  Å          γ   =  90  °  
a  =  17.8900(3)  Å          α   =  90°  
b  =  10.4590(2)  Å        β   =  94.2360(7)°  
c=  21.9190  (5)  Å          γ   =  90  °  
Volume   2640(4)  Å3   4090.09(14)  
Z   4   4  
Density  (calculated)   1,590  Mg/m3   1.602  Mg/m3  
Absorption  coefficient   1,041  mm-­‐‑1   1.712  mm-­‐‑1  
F(000)   1292   2000  
Crystal  size   0,21  X  0,18  x  0,16  mm3   0.28  x  0.25  x  0.25  mm3  
Theta  range  for  data  collection   2,05  a  24,95  °   1.42  to  27.90°  
Reflections  collected   2420   26411  
Independent  reflections   2420  [R(int)  =  0,0000]   9714  [R(int)  =  0.0388]  
Absorption  correction   Psi-­‐‑scans   multi-­‐‑scan  
Max.  and  min.  transmission   0,8511  y  0,8110   0.959,  1.036  
Refinement  method     Full-­‐‑matrix  least.squares  on  F2   Full-­‐‑matrix  least.squares  on  F2  
Data  /  restraints  /  parameters   2420/  1/  361   9714/  0  /  535  
Final  R  indices  [I>2sigma(I)]   R1  =  0,0630,  wR2  =  0,1137   R1  =  0.0379,  wR2  =  0.0808  
R  indices  (all  data)   R1  =  0,1330,  wR2  =  0,1392   R1  =  0.0592  and  wR2  =  0.0860  
Largest  dic.  peak  and  hole   0,296  y  –0,419  e.A-­‐‑3   0.431,  -­‐‑0.469  e.A-­‐‑3  
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67 
Table  2:  Selected  bond  lenghts  (Å)  and  angles  (°)  for  Cu(sac)2(Hpz)3,  and  [Cu3(sac)2(Hpz)3(pz)3)2(OH)].  
  
Cu(sac)2(Hpz)3  
  
Cu-­‐‑N(3)   1.986(9)   S(1)-­‐‑O(3)   1.453(11)   N(7)-­‐‑Cu-­‐‑N(2)   92.8(5)  
Cu-­‐‑N(7)   2,008(11)   S(2)-­‐‑O(5)   1.455(8)   N(5)-­‐‑Cu-­‐‑N(2)   89.1(5)  
Cu-­‐‑N(5)   2,012(10)   S(2)-­‐‑O(6)   1.430(9)   N(3)-­‐‑Cu-­‐‑O(1)   120.4(4)  
Cu-­‐‑N(2)   2,024(8)         N(7)-­‐‑Cu-­‐‑O(1)   87.3(4)  
Cu-­‐‑O(1)   2,115(9)   N(3)-­‐‑Cu-­‐‑N(7)   90,4(4)   N(5)-­‐‑Cu-­‐‑O(1)   90.0(4)  
C(3)-­‐‑O(12)   1,248(14)   N(3)-­‐‑Cu-­‐‑N(5)   89.6(4)   N(2)-­‐‑Cu-­‐‑O(1)   99.2(4)  
C(8)-­‐‑O4)   1,217(12)   N(7)-­‐‑Cu-­‐‑N(5)   177.0  (5)   N(7)-­‐‑Cu-­‐‑N(2)   92.8(5)  
S(1)-­‐‑O(2)   1.447(11)   N(2)-­‐‑Cu-­‐‑N(3)   140.4(4)        
  
  
[Cu3(sac)2(Hpz)3(pz)3)2(OH)]  
  
Cu(1)-­‐‑N(6)  
  
1.964(2)   Cu(3)-­‐‑N(4)   1.949(2)   N(6)-­‐‑Cu(1)-­‐‑N(1)   166.57(9)  
Cu(1)-­‐‑N(1)   1.965(2)   Cu(3)-­‐‑N(5)   1.953(2)   N(6)-­‐‑Cu(1)-­‐‑O(1)   87.60(8)  
Cu(1)-­‐‑N(22)   2,0216(11)   Cu(3)-­‐‑O(1)   1.9853(16)   N(1)-­‐‑Cu(1)-­‐‑O(1)   87,85(8)  
Cu(1)-­‐‑N(7)   2,008(2)   Cu(3)-­‐‑N(11)   2.012(2)   O(1)-­‐‑Cu(1)-­‐‑N(7)   164.62(8)  
Cu(1)-­‐‑O(1)   1.9943(16)   Cu(3)-­‐‑O(4)   2.5468(18)   N(3)-­‐‑Cu(2)-­‐‑N(2)   173.09(9)  
Cu(1)-­‐‑N(13)   2.343(2)   Cu(3)-­‐‑O(7)   2.8307(19)   O(1)-­‐‑Cu(2)-­‐‑N(9)   178.05(8)  
Cu(2)-­‐‑N(2)   1.971(2)   C(19)-­‐‑O(2)   1.236(3)   N(3)-­‐‑Cu(2)-­‐‑O(1)   88.68(8)  
Cu(2)-­‐‑O(1)   1.9832(16)   C(26)-­‐‑O(5)   1.237(3)   N(2)-­‐‑Cu(2)-­‐‑O(1)   88.34(8)  
Cu(2)-­‐‑N(9)   1.989(2)   S(1)-­‐‑O(4)   1.4470(18)   N(11)-­‐‑Cu(3)-­‐‑O(1)   176.52(8)  
Cu(2)-­‐‑O(3)   2.4981(18)   S(2)-­‐‑O(7)   1.4455(19)   N(4)-­‐‑Cu(3)-­‐‑N(5)   176.90(9)  
Cu(2)-­‐‑O(5)   2.7079(18)   S(2)-­‐‑O(6)   1.4414(19)   O(1)-­‐‑Cu(3)-­‐‑N(4)   88.92(8)  
                N(5)-­‐‑Cu(3)-­‐‑O(1)   88.04(8)  
      Cu(3)-­‐‑N(4)   1.949(2)   N(6)-­‐‑Cu(1)-­‐‑N(1)   166.57(9)  
            Cu(1)-­‐‑O(1)-­‐‑Cu(2)   114.64(8)  
            Cu(1)-­‐‑O(1)-­‐‑Cu(3)   117.27(8)  
            Cu(2)-­‐‑O(1)-­‐‑Cu(3)   116.65(8)  
  
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
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a                         b       
c   
Figure  2:  a.  Drawing  of  the  compound  2  showing  50%  probability  displacement,  b,    detail  of  the  
saccharinate  interactions  with  the  copper  ions,  c,  and  plane  of  the  molecule,  c.  
  
  
Spectroscopic  properties  
  
The  principal  IR  bands  and  magnetic  data  are  shown  in  table  4.  The  compounds  
of  this  work  show  different  IR  patterns,  due  to  the  different  ligand  coordination  around  
the  central  ion.  The  compounds  1,  2  and  3  show  bands  between  3300  cm-­‐‑1  and  3100  cm-­‐‑1  
due   to   the  pyrazole  ν(N-­‐‑H)   bands.   Free  pyrazole  molecule   shows   several   strong  N-­‐‑H  
stretching  bands  between  3300  and  2600  cm-­‐‑1.      
The  assignment  of  the  ν(C=O)  mode  in  the  IR  spectra  of  the  four  compounds  was  
made  by  taking  into  account  a  number  of  previous  assignments  and  calculations  [16,  17,  
18].   Complexes   1   and   3   show   N-­‐‑   and   O-­‐‑coordinated   saccharinate   molecules,   that   is  
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69 
reflected  in  the  ν(C=O)  frequency  split  of  the  respective  carbonyl  stretchings,  amounting  
to  26  cm-­‐‑1.  In  complex  2,  the  ν(C=O)  frequency,  1632  cm-­‐‑1,  is  lower  than  the  N-­‐‑coordinate  
saccharainate   in   1   probably   due   to   the   higher   ionic   character   of   the   saccharinate   ions  
that   are   weak   N-­‐‑   bonded   to   copper   ion,   permiting   a   charge   delocalization   in   the  
molecule  with  a  reduction  of  the  electron  density  and  also  the  force  constant  of  the  C-­‐‑O  
bond.      
The   spectroscopic   data   are   consistent   with   penta-­‐‑coordination   geometry   and  
indicate  that  the  structure  showed  in  solid  state  is  preserved  when  in  solution.  The  λmax  
values  are  blue-­‐‑shifted,  respect  to  tetra-­‐‑hydrated  sacharinate  complexes,  as  expected  for  
pyrazole,  a  stronger  ligand  than  water  [20].    
  
Table  3:  Spectral  and  magnetic  data  for  the  compounds.  
  
N° Complex
Electronic  
spectra
1 Cu(sac) 2 (pz) 3 3279/3136 1663/1637 1154 645  (81) 1.90
2 [Cu3(sac)2(Hpz)3(pz)3)2(OH)] 3322 1630 1148
-­‐‑1.92,                                  
-­‐‑2.24,              
2.15
3 Cu2 (sac) 4 (imid) 4 3366/3340 1673 1156/1168 699(90)
2.60,                  
-­‐‑2.17,          
2.14
λmax  /nm            
ε/  mol-­‐‑1  cm-­‐‑1
Infrared  spectra
µμeff/µμB,  
J/cm-­‐‑1,  g
νas(S=O) νs(S=O)
1290
1273
1287
ν(O-­‐‑H) ν(  N-­‐‑H) ν(C=O)
  
  
Magnetic  properties  
  
The   effective   magnetic   moments   at   room   temperature   for   1,   1.90   µμB,   is   in   the  
range  expected  for  mononuclear  copper(II)  complexes.      
To  investigate  the  magnetic  behavior  of  the  multinuclear  copper  complexes  2  and  3,  the  
magnetic  susceptibility  of  these  compounds  was  measured  in  the  temperature  range  of  
2-­‐‑300  K.  
The  temperature  dependence  of  µμeff  for  compound  2  is  given  in  Figure  3.  At  room  
temperature  µμeff   is   very   low   (1.92  µμB)  with   respect   to   the   value   expected   for   the   three  
independent   Cu(II)   ions   (around   3   µμB).   As   the   temperature   is   lowered   µμeff   decreases,  
reaching  a  value  around  1.73  µμB  at  70  –  50  K,  which  correspond  to  the  spin-­‐‑only  value  
for  one  unpaired  electron.  This  behavior  indicates  a  moderate  strong  antiferromagnetic  
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
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interaction   between   the   copper   ions,   with   an   unpaired   electron   per   Cu3   unit   in   the  
ground   state;   the   µμeff   value   keeps   on   decreasing   below   the   50   K   until   2K,   reaching   a  
value   of   1.49   µμB.      as   observed   in   similar   compounds   [15].   Considering   that   the   three  
metals  are  structurally  almost  equivalent,  it  can  be  assumed  that  the  exchange  coupling  
constants  are  identical,  J1  =  J2  =  J3  =  J,  so  the  spin  Hamiltonian  H  =  -­‐‑J(S1S2  +S2S3  +S1S3)    will  
describe      the   interactions   of   the   spins.   From   this   Hamiltonian,   a   solution   of   magnet  
susceptibility  may  be  derived  as  follows:  
χM  =   (Nβ2g2/4kT)[1   +   5exp(3J/2kT)]/[1   +   exp(3J/2kT)],  where  N,  g,  β,   k  and  T     have   their  
usual  meanings.  
Due   to   the   low   temperature   behavior,   the   Weiss   correction   parameter   Θ   was  
included,   for   possible   intertrimer   magnetic   interaction   (T   replaced   by   T-­‐‑Θ).   The  
simulation   of   the   susceptibility   data   using   the   above  Hamiltonian,   fit   to   J   =   -­‐‑212   cm-­‐‑1  
with    g=  g1  =  g2  =  g3  =  2.06  ,  a  temperature  independent  paramagnetism  (TIP)  of  200  10-­‐‑6    
cm3  mol-­‐‑1  and    a  Weiss  temperature  of    -­‐‑3  K.    Attempts  at  getting  a  better  fit  by  using  an  
equation  with  two  different  J  values  (so  treating  the  system  as  an  isosceles  triangle)  were  
also  performed.  The   J   and   J’   values  obtained,  very   similar,  did  not   significantly  differ  
from   those   obtained   with   only   one   J   value,   and   the   goodness   of   the   fitting   did   not  
improve.  
  The   obtained   J   value   is   consistent   with   reported   values   for   analogous  
compounds  that  are  around  200  cm-­‐‑1  [15].  
The   temperature  variation  of   the   effective  magnetic  moment  of  3   is   show   in  Figure   4.  
The  value  of  µμeff  2.60  µμB  decreases  with  decreasing  temperature  to  2.49  µμB  at     20  K  and  
1.06  µμB    at  2  K.  This  behavior  is  consistent  with  very  weak  antiferromagnetic  interaction  
between  the  copper(II)  ions.  The  data  were  fitting  using  the  Hamiltonian  H  =  -­‐‑2JS1S2,  the  
obtained   best   fit   parameters   are:   J   =   -­‐‑2.17   cm-­‐‑1,   g   =   2.14,   a   TIP   of   160   cm3   mol-­‐‑1,   a  
paramagnetic   impurity,   PI   =   0.2   %.      Similar   magnetic   data   were   obtained   for  
[Cu2(C6H3Cl2OCH2COO)4(bipyam)2],  C6H3Cl2OCH2COO  =  2,4  dichlorophenoxyacetato,  J  
=  -­‐‑0.8  cm-­‐‑1,  g  =  2.12  [20]  and    for  [Cu2  (2-­‐‑MeSnic)2(py)2]2,  J  =  -­‐‑0.65  cm-­‐‑1,  g  =  2.12,  2-­‐‑MeSnic  
=  2-­‐‑methylthionicotinate.  [22].    The  values  of  2J  for  these  compunds    -­‐‑4,34,                -­‐‑1.60  and  -­‐‑
1.30      suggest   that   the   magnetic   orbitals   are   unfavourably   oriented   to   provide   good  
overlap  for  a  magnetic  interaction.  [23]  
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0 50 100 150 200 250 300
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
µ e
ff/
µ B
Temperature, K
  
  
Figure  3:  Plot  of  the  magnetic  moment  of  [Cu3(sac)2(Hpz)3(pz)3)2(OH)]  as  a  function  of  temperature.    The  
solid  line  represent  the  best  fitting  curve.  
0 50 100 150 200 250 300
1,0
1,2
1,4
1,6
1,8
2,0
2,2
2,4
2,6
2,8
µ e
ff [
µ B
]
T[K]
  
Figure  4:    Plot  of  the  magnetic  moment  of  [Cu2(sac)4(Himid)4]  as  a  function  of  temperature.  The  solid  line  
represent  the  best  fitting  curve.  
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
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150 200 250 300 350 400 450
B [mT]
  
Figure  5:  EPR  spectrum  of  [Cu(sac)2(pyr)3]  in  dichloromethan  solution,  the  gray  line  is  the  best  
simulations  data.  
150 200 250 300 350 400 450
B[mT]
  
Figure  6:  EPR  spectrum  of  a  polycrystalline  sample  [Cu(sac)2(imid)2]2  in  dichloromethan  solution,  the  gray  
line  is  the  best  simulation  data.  
  
Electrochemistry  behavior  of  the  compounds  
  
The   redox   properties   of   the   complexes   1and   3,   were   determined   by   cyclic  
voltammetry   measurements,   carried   out   in   dimethylformamide   at   room   temperature  
with   a   scan   rate   of   100  mVs-­‐‑1.         For   compound   1   one   quasi-­‐‑reversible   single-­‐‑electron  
oxidation  wave  was  observed   (Figure  7),  and  an   irreversible   reduction  peak   for  1,   at   -­‐‑
0.23   V.   The   oxidation   half-­‐‑wave   potentials   were   0.43   and   0.45   V   respectively.    
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Compound  3  showed  a  reversible  one  electron  wave  at  0.3  V.,  IO/IR  =  1  and  ΔE  =  0.14  V,  
the  last  value  should  be  0.059,  but  due  to  the  solution  resistance  that  produce  big  wave  
peak  separation,   it  was  compared  with   the   ferrocene,  Fc/Fc+,  ΔE  value   (0.141  V)   in   the  
same  solution,  to  confirm  the  wave  reversibility.    In  table  4,  pKa  values  for  heterocyclic  
amine  and   the  E1/2   are  given.      Imidazole   is  more  basic  amine  and  has   the   smallest  E1/2  
value,  which  means  that  more  dative  character  can  stabilize  the  high  oxidation  state.    
  
  
Table  4.  Electrochemical  data  of  compounds  1,  3  and  4    and  pKa  values  for  the  correponding  
ligands.  
  
Compound   E1/2,  V   ΔE,  V   Pka,  
amine  
Cu(sac)2(pz)3   0,43  q,     0,18   2,48  
Cu2(sac)4(imid)4   0,31  r   0,14   6,99  
Fc/Fc+   0,61   0,14     
Synthesis,  characterization  and  redox  behaviour  of  mixed  ligand  copper(II)  saccharinate  complexes.  
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  a  
b  
  
Figure  7:  Cyclic  voltammogram  in  DMF/TBAPF6  0.1  mol  L-­‐‑1  on  a  glassy  carbon  electrode  vs  Ag/AgCl,    of  
the  copper  complexe  a  [Cu(sac)2(pyr)3],  b.  [Cu2(sac)4(imid)4].  
  
IV   CONCLUSIONS  
  
The  product  of  the  reaction  between  copper  saccharinate  and  pyrazole,  depends  
on   the   reaction   conditions.   If   the   reaction   is  made   in  water   solution      the  products   are  
[Cu(sac)2(Hpz)2(H2O)2]   [10]   and      [Cu(sac)2(Hpz)4]   [11],   the  difference   lies  maybe   in   the  
water   amount   used   for   the   reaction,   because   the  mol   ratios   of   Cu   complex/   pyrazole  
were  the  same  in  both  cases.    The  reaction  in  methanol  produces  also  two  compounds,  
in   this   case   from   the   same   reaction,   [Cu(sac)2(Hpz)3]   and   [Cu3(sac)2(Hpz)3(pz)3)2(OH)].  
The  last  compound  is  the  result  of  the  auto-­‐‑deprotonation  of  pyrazole,  pKa  =  2.48.  This  
compound  was  reproduced  from  the  reaction  in  basic  media.  Imidazole  gave  the  same  
compound  independent  of  the  reaction  media,  water,  methanol  or  DMF.  They  have  the  
same  size,  the  basicity  could  be  a  reason,  Imidazole  pka  =  6.99  and  pyrazole  2.48.  [24].      
  
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V   REFERENCES  
  
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Acknowledgements  
We   are   grateful   to   the  Vicerrectoría   de   Investigación,  University   of   Costa   Rica;  
(Grant  No.  115-­‐‑98  375)  for  financial  suport.  GVB  thanks  DAAD  for  a  research  fellowship  
and   Prof.   Karl  Wieghardt   for   the   use   of   research   facilities   at  Max-­‐‑Planck-­‐‑Institute   for  
Bioinorganic   Chemistry.   Funding   was   also   provided   by   the   Ministry   of   Science   and  
Innovation   (Spain)   under   Grant   MAT2008-­‐‑04350   and   CONSOLIDER-­‐‑INGENIO   in  
Molecular  Nanoscience,  ref.  CSD  2007-­‐‑00010,  and  by  the  Diputación  General  de  Aragón  
(Spain)  
  
Appendix.    Supplementary  material  
Crystallographic  data  for  the  structures  reported  in  this  paper  have  been  deposited  with  
the  Cambridge  crystallographic  Data  Center  as  supplementary  publication  Nos  784928  
(1)  &  784929  (2).  Copies  of  the  data  can  be  obtained  free  of  charge  on  application  to  The  
Director,CCDC,  12  Union  Road,  Cambridge  CB2  1EZ,  UK,  fax:  int.code+(1223)336-­‐‑033:  e-­‐‑
mail  for  inquiry:  fileserv@ccdc.cam.ac.uk.