Transcript Bonding in complexes of d-block metal ions – Crystal Field

‫تفترض هذه النظرية على ان المعقدات الفلرية عبارة هن تداخل‬
‫الكتروستاتيكي ( يعني تآصر ايوني ) بين الذرة المركزية (تعتبر كشحنة نقطية‬
‫موجبة تحتوي على اوربيتاالت ‪ d‬الخمسة ) و الليكاندات المحيطة بها (كشحنة‬
‫نقطية سالبة تنجذب نحو الشحنات الموجبة و يحدث التآصر ‪ ,‬وقد فسرت هذه‬
‫النظرية االلوان و السلوك المغناطيسي و الطيفي للمعقدات‪.‬‬
‫األيون الفلزي وتأثير اقتراب‬
‫الليكاندات‬
‫اوربيتاالت ‪ d‬والتوزيع الفراغي لها على طول المحاور‬
‫‪Linear combination of‬‬
‫‪dz2-dx2 and dz2-dy2‬‬
‫‪d2z2-x2-y2‬‬
Octahedral Field
The d-orbitals:
z
z
y
dyz
the t2g
set
x
z
y
x
dxy
z
x
dxz
z
y
dz2
y
x
y
dx2-y2
x
the eg
set
‫‪Splitting of the d sub-shell in octahedral‬‬
‫‪coordination‬‬
‫اوربيتاالت الليكاند الواهبة‬
‫اوربيتاالت ‪eg‬‬
‫اوربيتاالت‬
‫‪z‬‬
‫‪z‬‬
‫‪z‬‬
‫‪y‬‬
‫‪y‬‬
‫‪x‬‬
‫‪dx2-y2‬‬
‫‪t2g‬‬
‫‪y‬‬
‫‪x‬‬
‫‪dz2‬‬
‫الذين يتجهان ‪dz2,dx2-y2‬أوربيتالي‬
‫مباشرة نحو الشحنات السالبة‬
‫‪x‬‬
‫‪dyz‬‬
‫ألن فصوصها ‪t2g‬‬
‫تتجه مابين‬
‫االحداثيات‬
Splitting of d-orbital energies by an
octahedral field of ligands.
D is the splitting energy
+0.6Δ₀
- o.4Δ₀
‫توزيع االلكترونات في حالة المجال الضعيف و القوي‬
‫توزيع االلكترونات في حالة المجال الضعيف و القوي‬
‫قياس مقدارطاقة انفصام المجال البلوري ‪Δ₀‬‬
‫‪Crystal-Field Theory‬‬
‫‪[Ti(H2O)6]3+‬‬
Color of Transition Metal
Complexes
DE = E2 - E1 = hn = hc
l
or
l=
hc
DE
Orbital occupancy for high- and low-spin
complexes of d4 through d7 metal ions.
high spin:
weak-field
ligand
low spin:
strongfield
ligand
high spin:
weak-field
ligand
low spin:
strongfield
ligand
High spin
Low spin
High-spin and Low-spin Complex
Ions of Mn2+
‫مجال قوي‬
‫خواص بارا مغناطيسية‬
‫مجال ضعيف‬
‫خواص بارامغناطيسية‬
‫‪High and low-spin complexes of d5 ions:‬‬
‫تكون في اغلب المعقدات طاقة االزدواج عالية لهذا تكون معقدات عالية البرم‬
‫أما مع الليكاندات القوية فتنتج طاقة كافية الزدواج االلكترونات وتكوين معقدات‬
‫ايونات ‪ d5‬بارامغناطيسية‬
‫‪[Fe(H2O)6]3+ Δ = 13,700 cm-1‬‬
‫‪P = 22,000 cm-1‬‬
‫‪eg‬‬
‫‪Δ<P‬‬
‫‪t2g‬‬
‫‪[Fe(CN)6]3- Δ = 35,000 cm-1‬‬
‫‪P = 19,000 cm-1‬‬
‫‪Paramagnetic‬‬
‫‪5 unpaired e’s‬‬
‫‪eg‬‬
‫‪paramagnetic‬‬
‫‪one unpaired e‬‬
‫‪Δ>P‬‬
‫‪energy‬‬
‫‪t2g‬‬
‫)‪low-spin d5 ([Fe(CN)6]3-‬‬
‫)‪high-spin d5 ([Fe(H2O)6]3+‬‬
‫تتوزع االلكترونات حسب قاعدة هوند اوربيتاالت تمال أوال بسبب قوة الليكاند ‪t2g‬‬
Splitting of the d sub-shell in
an octahedral complex
energy
eg
Δ
3d sub-shell
Co3+ ion
in gas-phase
(d6)
d-shell
split by
presence
of ligand
donor-atoms
t2g
Co(III) in
octahedral
complex
High and low-spin complexes:
energy
eg
Paramagnetic
4 unpaired e’s
Δ > P diamagnetic
no unpaired e’s
t2g
low-spin d6
t2g ‫اوربيتاالت تمال أوال بسبب قوة‬
‫الليكاند‬
eg
Δ<P
t2g
high-spin d6
‫تتوزع االلكترونات حسب قاعدة‬
‫هوند‬
High and low-spin complexes of some d6 ions:
[CoF6]3- Δ = 13,100 cm-1
P = 22,000 cm-1
[Co(CN)6]3- Δ = 34,800 cm-1
P = 19,000 cm-1
eg
energy
Δ >> P
t2g
low-spin d6 ([Co(CN)6]4-)
Paramagnetic
4 unpaired e’s
diamagnetic
no unpaired e’s
eg
Δ<P
t2g
high-spin d5 ([CoF6]3-)
‫‪High and low-spin complexes of d7 ions:‬‬
‫نفس العدد من االلكترونات و االختالف بحالة التأكسد‬
‫‪[Co(H2O)6]2+ Δ = 9,300 cm-1‬‬
‫‪eg‬‬
‫‪Δ<P‬‬
‫‪[Ni(bipy)3]3+‬‬
‫‪Paramagnetic‬‬
‫‪3 unpaired e’s‬‬
‫‪eg‬‬
‫‪paramagnetic‬‬
‫‪one unpaired e‬‬
‫‪Δ>P‬‬
‫‪t2g‬‬
‫)‪high-spin d7 ([Co(H2O)6]3+‬‬
‫تملئ االوربيتاالت بااللكترونات حسب‬
‫قاعدة هوند‬
‫‪energy‬‬
‫‪t2g‬‬
‫)‪low-spin d7 ([Ni(bipy)3]3+‬‬
‫تملئ االوربيتاالت الواطئة الطاقة ومن ثم‬
‫‪.‬االوربيتاالت العالية الطاقة‬
‫‪Crystal-Field Theory‬‬
‫‪Weak-field ligands‬‬
‫)تمتلك ‪(small D‬‬
‫تميل االلكترونات الى‬
‫االنتقال إلى االوربيتاالت‬
‫العالية الطاقة على ازدواج‬
‫‪.‬االلكترونات‬
‫)تمتلك ‪Strong-field ligands (large D‬‬
‫تميل الى الملئ التدريجي لاللكترونات في االوربيتاالت الواطئة الطاقة‬
‫‪High and Low Spin Octahedral Complexes‬‬
‫المعقدات العالية البرم و الواطئة البرم ممكنة في الترتيب االلكتروني ‪d4, d5, d6, and d7‬‬
Crystal Field Splitting Energy (CFSE)
• In Octahedral field, configuration is: t2gn egn
CFSE = -0.4 Δo
nt2g + 0.6 Δo neg
DO = 10 Dq
• In weak field: DO  P, => t2g3eg1
• In strong field DO  P, => t2g4
• P - paring energy
‫‪ CFSE ‬حساب طاقة استقرار المجال البلوري‬
‫‪t2g3 eg0‬‬
‫‪CFSE = -1.2 Δ₀‬‬
‫‪t2g2 eg0‬‬
‫‪CFSE =-0.8 Δ₀‬‬
‫ويبين الجدول التالي ملخص لتركيب وطاقة استقرار المجال البلوري )‪ )CFSE‬وعدد االلكترونات‬
‫المزدوجة للتراكيب من ‪ d1→d10‬في حالتي المجال الضعيف و المجال القوي ‪:‬‬
P
P
P
P
P
3P
3P
3[Fe(CN)6]
Example: explain
+3
[Fe(H2O)6] more stable?
[Fe(CN)6]3- Δ = 35,000 cm-1
P = 22,000 cm-1
eg
energy
Δ>P
t2g
CFSE=(5X-0.4Δ₀)+(0X0.6Δ₀) +2P
=-2.0Δ₀ + 2P
or
[Fe(H2O)6]3+ Δ = 13,700 cm-1
P = 22,000 cm-1
eg
Δ<P
t2g
CFSE=(3X-0.4Δ₀)+(2X0.6Δ₀)
=-1.2Δ₀ + 1.2Δ₀ = 0
Crystal Field Stabilization Energy
(CFSE) of d5 and d10 ions:
The CFSE for high-spin d5 and for d10 complexes is
calculated to be zero:
[Zn(en)3]3+
[Mn(NH3)6]2+:
energy
eg
eg
t2g
t2g
Δ = 22,900 cm-1
Δ = not known
CFSE = 10,000(0.4 x 3 – 0.6 x 2)
= 0 cm-1
CFSE = Δ(0.4 x 6 – 0.6 x 4)
=
0 cm-1
‫جدول يبين قيم طاقة استقرار المجال البلوري وطاقة االزدواج لبعض المعقدات‬
‫هذه المعقدات لها نفس العدد التناسقي وااليون الفلزي وااليون المرافق •‬
‫‪Effect of ligands on the colors of‬‬
‫‪coordination compounds‬‬
‫‪Slide of‬‬
‫‪53‬‬
Tetrahedral & Square Planar Ligand
Field
Figure 20.28: Crystal field diagrams for octahedral and
tetrahedral complexes
‫مستويات الطاقة النفصام اوربيتاالت للمعقدات‬
‫الرباعية السطوح و المربع المستوي‬
‫‪square planar‬‬
‫‪tetrahedral‬‬
‫متثيل انفصام اوربيتاالت ملعقدات املربع املستوي‬
square planer
Z out
octahedral
dx2-y2
dx2-y2
eg
dx2-y2
dz2
dz2
dxy
dxy
t2g
dz2
dxy
dxz dyz
dxz dyz
dxz dyz
‫ايونات ‪d8‬تكون معقدات مربعة مستوية‬
‫تجريبيا ً وجد إن المربع المستوي هو ناتج من‬
‫إزالة ليكاندين من المعقدات الثمانية السطوح‬
‫‪L‬‬
‫‪L‬‬
‫‪dx2-y2‬‬
‫‪M‬‬
‫‪L‬‬
‫‪L‬‬
‫‪z‬‬
‫‪L‬‬
‫‪y‬‬
‫‪L‬‬
‫‪L‬‬
‫‪x‬‬
‫‪M‬‬
‫‪L‬‬
‫‪dx2-y2‬‬
‫‪dz2‬‬
‫‪dxy‬‬
‫‪dz2‬‬
‫‪dxy‬‬
‫‪dxz,dyz‬‬
‫‪dxz,dyz‬‬
‫‪Square Planar‬‬
‫‪Octahedral‬‬
‫‪L‬‬
‫‪L‬‬
dn
High spin (HS)
Low spin (LS)
Tetrahedral
d
Octahedral
Octahedral
Complexes
d1
Complexes
-0.4
complexes
-o.4
-0.6
d2
-0.8
-0.8
-1.2
d3
-1.2
-1.2
-0.8
d4
-o.6
-1.6
-o.4
d5
0
-2.0
0
d6
-0.4
-2.4
-0.6
d7
-0.8
-1.8
-1.2
d8
-1.2
-1.2
-0.8
d9
-0.6
-0.6
-0.4
d10
0
0
0
‫ويالحظ في المعقدات الرباعية السطوح إن اعلي‬
‫استقرارية يضفيها المجال الليـــــكاندي هي في‬
‫نظـــــــــــــــــامي )‪ d2,d7(high spin‬ولهذا‬
‫السبب يتخذ نظام ‪ d2‬أو ‪ d7‬الشكل المنتظم لرباعي‬
‫السطوح‪.‬‬
‫‪3‬‬
‫‪8‬‬
‫‪3+‬‬
‫‪2+‬‬
‫ً‬
‫‪ d (Cr , Ni‬و ‪ d‬لوحظ تجريبيا أن االيونين‬
‫يفضالن إلى حد كبير التناظر الثماني السطوح ‪,‬‬
dx2-y2
dx2-y2
dz 2
dxy
dxz,dyz
dxy
dxy
dxz,dyz
dx2-y2
dz 2
H2O
H2O
Ni
dxz,dyz
Tetrahedral
Octahedral
OH2
dz2
2
OH2
Cl
OH2
H2O
Octahedral
Coordination number =6
Ni(II) d8 S = 1
Cl
Square Planar
2-
N
N
Cl
C
C
Ni
2-
Ni
Cl
Tetrahedral (CN=4)
C
N
C
N
Square Planar (CN=4)
Ni(II) d8 S =1
Ni(II) d8 S = 0
The spectrochemical series:
One notices that with different metal ions the order of
increasing Δ with different ligands is always the same.
Thus, all metal ions produce the highest value of Δ in their
hexacyano complex, while the hexafluoro complex always
produces a low value of Δ. One has seen how in this course
the theme is always a search for patterns. Thus, the increase
in Δ with changing ligand can be placed in an order known
as the spectrochemical series, which in abbreviated form is:
I- < Br- < Cl- < F- < OH- ≈ H2O < NH3 < CN-
The spectrochemical series:
The place of a ligand in the spectrochemical series is determined
largely by its donor atoms. Thus, all N-donor ligands are close to
ammonia in the spectrochemical series, while all O-donor ligands are
close to water. The spectrochemical series follows the positions of the
donor atoms in the periodic table as:
F
O
N
Cl
S
P
C
?
very little
data on
P-donors –
may be higher
than N-donors
Br
I
S-donors ≈
between Br
and Cl
spectrochemical
series follows
arrows around
starting at I and
ending at C
The spectrochemical series:
Thus, we can predict that O-donor ligands such as oxalate or
acetylacetonate will be close to water in the spectrochemical series. It
should be noted that while en and dien are close to ammonia in the
spectrochemical series, 2,2’bipyridyl and 1,10-phenanthroline are
considerably higher than ammonia because their sp2 hybridized Ndonors are more covalent in their bonding than the sp3 hybridized
donors of ammonia.
O
O
-
-
O
O
oxalate
H2N
dien
N
H
H3C
CH3
O
H2N
O-
acetylacetonate
NH 2
N
bipyridyl
N
NH 2
en
N
N
1,10-phen
The bonding interpretation of
the spectrochemical series:
For the first row of donor atoms in the periodic table,
namely C, N, O, and F, it is clear that what we are seeing in
the variation of Δ is covalence. Thus, C-donor ligands such
as CN- and CO produce the highest values of Δ because the
overlap between the orbitals of the C-atom and those of the
metal are largest. For the highly electronegative F- ion the
bonding is very ionic, and overlap is much smaller. For the
heavier donor atoms, one might expect from their low
electronegativity, more covalent bonding, and hence larger
values of Δ. It appears that Δ is reduced in size because of
π–overlap from the lone pairs on the donor atom, and the
t2g set orbitals, which raises the energy of the t2g set, and so
lowers Δ.
Crystal Field Stabilization
Energy (CFSE):
When splitting of the d sub-shell occurs, the occupation of
the lower energy t2g level by electrons causes a stabilization
of the complex, whereas occupation of the eg level causes a
rise in energy. Calculations show that the t2g level drops by
0.4Δ, whereas the eg level is raised by 0.6Δ. This means
that the overall change in energy, the CFSE, will be given
by:
0.6n(eg))
- Δ(0.4n(t2g)
CFSE =
where n(t2g) and n(eg) are the numbers of electrons in
the t2g and eg levels respectively.
Calculation of Crystal Field
Stabilization Energy (CFSE):
The CFSE for some complexes is calculated to be:
[Cr(en)3]3+
[Co(NH3)6]3+:
energy
eg
eg
t2g
t2g
Δ = 22,900 cm-1
Δ = 21,900 cm-1
CFSE = 22,900(0.4 x 6 – 0.6 x 0)
= 54,960 cm-1
CFSE = 21,900(0.4 x 3 – 0.6 x 0)
=
26,280 cm-1
Crystal Field Stabilization Energy
(CFSE) of d0 to d10 M(II) ions:
For M(II) ions with the same set of ligands, the variation of Δ is not large. One
can therefore use the equation for CFSE to calculate CFSE in terms of Δ for d0
through d10 M(II) ions (all metal ions high-spin):
Ca(II) Sc(II) Ti(II) V(II) Cr(II) Mn(II) Fe(II) Co(II) Ni(II) Cu(II)
Zn(II)
d0
d1
d2
d3 d4
d5
d6
d7
d8
d9
d10
CFSE: 0
0.4Δ 0.8Δ
1.2Δ 0.6Δ 0
0.4Δ
0.8Δ 1.2Δ 0.6Δ
This pattern of variation CFSE leads to greater stabilization in the complexes of
metal ions with high CFSE, such as Ni(II), and lower stabilization for the
complexes of M(II) ions with no CFSE, e.g. Ca(II), Mn(II), and Zn(II). The
variation in CFSE can be compared with the log K1 values for EDTA
complexes on the next slide:
0
Crystal Field Stabilization Energy (CFSE) of
d0 to d10 M(II) ions:
CFSE as a function of no of delectrons
doublehumped
curve
1.4
CFSE in multiples of Δ.
Ni2+
1.2
1
0.8
0.6
0.4
0.2
0
Ca2+0
1
2
3
4
5
6
Mn72+ 8
no of d-electrons
9
10 112+
Zn
Log K1(EDTA) of d0 to d10 M(II) ions:
log K1(EDTA) as a function of no of delectrons
= CFSE
logK1(EDTA).
20
doublehumped
curve
18
16
Zn2+
14
Mn2+
12
Ca2+
10
0
1
2
3
4
5
6
rising baseline
due to ionic
contraction
7
no of d-electrons
8
9
10 11
Log K1(en) of d0 to d10 M(II) ions:
log K1(en) as a function of no of delectrons
= CFSE
12
doublehumped
curve
logK1(en).
10
8
6
Zn2+
4
Ca2+
2
rising baseline
due to ionic
contraction
Mn2+
0
0
1
2
3
4
5
6
7
no of d-electrons
8
9
10 11
Log K1(tpen) of d0 to d10 M(II) ions:
log K1(tpen) as a function of no of delectrons
doublehumped
curve
logK1(tpen).
20
15
Zn2+
10
Mn2+
5
N
N
N
N
N
tpen
N
Ca2+
0
0
1
2
3
4
5
6
7
no of d-electrons
8
9
10 11
The Irving-Williams Stability Order:
Irving and Williams noted that because of CFSE, the log K1
values for virtually all complexes of first row d-block metal
ions followed the order:
Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) >
Zn(II)
We see that this order holds for the ligand EDTA, en, and
TPEN on the previous slides. One notes that Cu(II) does
not follow the order predicted by CFSE, which would have
Ni(II) > Cu(II). This will be discussed under Jahn-Teller
distortion of Cu(II) complexes, which leads to additional
stabilization for Cu(II) complexes over what would be
expected from the variation in CFSE.