56M.Liu et al./Reactive&Functional Polymers44(2000)55–64
increased the activity while the high selectivity supplied by Beijing Chemicals.Absolute etha-(selectivity to chloroaniline.99.9%)remained nol[16],anhydrous cobalt(II)chloride,and constant[13,14].Therefore,further research anhydrous nickel(II)chloride were prepared should be done to explain the nature of the according to the literature[17],respectively. modification effect of some metal cations in the
2.2.Equipment
selective hydrogenation over the polymer-stabi-
lized metal colloids.
All ultraviolet visible spectra were obtained We suspected that the charge distribution and
on a Hitachi340type spectrophotometer.In-electronic properties of the catalysts were
frared spectra were recorded on a Bruker IFS-IS changed upon the adsorption of metal cations on
spectrophotometer.Chemical analysis was car-the metal colloids.Hence,the change in elec-
ried out by means of inductively coupled plas-tronic and conformational properties as well as
ma optical emission spectroscopy(ICP).The the coordination ability of the surface metal
spectrometer was a Spex1702scanning ICP atoms,which are main factors influencing the
spectrometer.
activity and the selectivity of the catalyst,
should be determined by the adsorption of
n1
2.3.Preparation of PVP-M complexes different amounts of the metal cations.How-
ever,in the course of examining the adsorption2131
Metal cation solutions of Co and Fe of nickel(II)chloride on PVP-stabilized
were prepared from chloride salts in ethanol platinum colloid,it was found that the con-
solution.Polymer complex formation of a metal centration of nickel(II)had hardly changed after
cation with PVP was performed by addition of adsorption.This was probably due to the
PVP ethanol solution(1.0M,10.0ml)to a amount of the adsorption being too small to
metal cation ethanol solution(0.15M,7.0ml) give a precise result.On the other hand,the
to give amorphous precipitate.The resulting evidence of interaction between metal cations
precipitate was centrifuged,washed with several and the reactants[10]or the products[12]have
portions of acetone until the color of washing been reported.Interaction between PVP and
liquor turned into colorless,and then dried in palladium colloidal particles[15]has also been
vacuo at room temperature.The blue precipitate reported.When PVP is used as a stabilizer for21
of PVP-Co complex and the light yellow metal colloids,it is possible that the metal31
precipitate of PVP-Fe complex were desig-cations interact with the oxygen or nitrogen2131
nated as PVP-Co(2)and PVP-Fe(4), atoms on thefive-membered nitrogen-contain-31
respectively.Another sample of the PVP-Fe ing heterocycles of PVP.This interaction may31
complex designated as PVP-Fe(3)was ob-affect the properties of the metal colloids,and
tained by adding PVP ethanol solution(0.2M, consequently influence the catalytic perform-
10.0ml)to ferric ethanol solution(0.02M,10.0 ance.Under this consideration,we investigated
ml).However,we failed to obtain the solid the interaction between PVP and metal cations.21
PVP-Ni complex by various tests even by
adding1.0M concentrated PVP ethanol solution
21
to the saturated Ni ethanol solution.
2.Experimental
2.1.Materials
3.Results and discussion
Poly(N-vinyl-2-pyrrolidone)(av.M10000)  3.1.Spectrophotometric measurements
w
was purchased from BASF,dried under vacuum
below1008C for6h,and stored in a drybox IR spectroscopy is useful for detecting the before use.Other analytical grade reagents were interaction between two species.Wuepper and
M.Liu et al./Reactive&Functional Polymers44(2000)55–6457
31 Popov[18]reported that a shift of carbonyl becomes somewhat asymmetric on adding Fe,
2121
band was observed in the IR spectrum of2-Co and Ni,and the C=O stretching fre-pyrrolidone in the presence of alkali metal ions.quencies of the complexes are almost the same They concluded that the
band shift was due to as that of the free ligand,indicating that the
n1
the interaction between the carbonyl oxygen of interaction between PVP and M in methanol 2-pyrrolidone and the metal ions.The IR spectra solution is very weak.Fig.1b gives the IR n131
of PVP-M complexes in methanol solution spectra of PVP,PVP-Fe complex and PVP-
21
and in solid state are shown in Fig.1a and b,Co complex in the solid state,respectively.
n1
respectively.The spectra of the PVP-M com-The carbonyl band of PVP appears at1661.5
21
plexes in solid state are somewhat different cm characteristic of uncomplexed pyrrol-
21
from that in methanol solution.As shown in idone,whereas it shifts to1655.7cm in PVP-
212131
Fig.1a,the peak of C=O double bond in PVP Co,and1656.2cm in PVP-Fe complex,
n1312121 Fig.1.The IR spectra of PVP and PVP-M(a)in MeOH(298.0K,0.25M):PVP(1),PVP-Fe(2),PVP-Co(3)and PVP-Ni(4);
213131
(b)of powder samples:PVP(1),PVP-Co(2),PVP-Fe(3),and PVP-Fe(4).
58M.Liu et al./Reactive&Functional Polymers44(2000)55–64
reactive metal
respectively.It should be noted that the band absolute ethanol are given,respectively(Figs. shift is considerably greater than the one ob-2–5).It can be seen from Figs.2and3that the served in methanol solution showing that in interaction between PVP and metal cations in solution there is a competition of solvent mole-absolute ethanol was stronger than that in water. cules with PVP.In addition,the shift of car-This is attributed to the two reasons:(1)the
21solvated metal cations were formed in water and bonyl band in the PVP-Co complex is a little
31in absolute ethanol,and the aquo cations were larger than that in the PVP-Fe complex.It is
more stable than the alcohol-solvated metal consistent with the Irving–Williams rule[19–
cations;(2)the hydrogen bonding of PVP with 21],i.e.the magnitudes of the band shifts upon
water was stronger than that of PVP with the metal complex formation follow the order:
alcohol.
Mn(II),Fe(II),Co(II),Ni(II),Cu(II).
2121
The absorbances of Co and PVP-Co in Zn(II).
absolute ethanol were0.450and0.567at659 As shown in Fig.1b,the peak of C=O double
31nm,and were0.024and0.152at304nm, bond in PVP-Fe becomes more asymmetric
21respectively(Fig.3).This indicated the pres-than that in PVP-Co.This suggested that the
21
3131ence of interaction between Co and PVP.Fig. interaction between PVP and Fe in PVP-Fe
214illustrates that there was an interaction be-complex is stronger than that in the PVP-Co
21
tween Ni and PVP for the absorbances of complex.
2121
Ni and PVP-Ni in absolute ethanol were UV-VIS spectroscopy is another convenient
0.075and0.084at412nm,respectively.The method to investigate the coordination com-
21
interaction between Ni and PVP is weaker pounds.The UV-VIS spectra of metal cations
21 312121than that in the PVP-Co system.An obvious (Fe,Co and Ni)and PVP in water and
212121 Fig.2.The UV-VIS spectra of PVP(1),Co(2)and PVP-Co(3)in water at286.5K.PVP:0.225M,Co:0.12M.
M.Liu et al./Reactive&Functional Polymers44(2000)55–6459
2121222123 Fig.3.The UV-VIS spectra of Co(1)and PVP-Co(2)in absolute ethanol at286.5K.PVP:4310M,Co:4310M.
21212122 Fig.4.The UV-VIS spectra of Ni(1)and PVP-Ni(2)in absolute ethanol at286.5K.PVP:0.2M,Ni:1310M.