Supporting Information – Modelling Details
Title: Modelling Gas Separation in Metal-Organic Frameworks
Journal: Adsorption
Authors: Brad A Wells and Alan L Chaffee
Affiliation: Cooperative Research Centre for Greenhouse Gas Technologies, School
of Chemistry, Monash University, Victoria, Australia.
Email: Alan.Chaffee@sci.monash.edu.au
Gas Molecules
Gas Geometries
Table 1 details the bond length and bond angle that defines each of the gas molecule
geometries.
Gas Molecule
Carbon Dioxide
Water
Nitrogen
Hydrogen
Methane
Bond Length / Ǻ
1.1600
0.9570
1.0977
0.7412
1.1010
Bond Angle / degrees
180.0
104.52
109.471
Table 1: Geometrical parameters of gas molecules
Gas Internal Forcefield
To parameterise the gas internal forcefield, each atom is assigned a type. Table 2
shows the atomic parameters of forcefield types for each gas atom.
Gas
Forcefield
ε
Atom
σ/Ǻ
Charge
Molecule
Type
/ kcal mol-1
CO2
C
c2=
3.9150
0.0680
0.670
CO2
O
o1=*
3.3600
0.0670
-0.335
H2O
H
h1o
1.0870
0.0080
-0.66
H2O
O
o2*
3.8400
0.0800
0.330
N2
N
n1n
3.8008
0.0598
0.000
H2
H
h1h
1.4210
0.0216
0.000
CH4
C
c40
4.0530
0.0700
-0.212
CH4
H
h1
2.8780
0.0230
0.053
Table 2: Atomic forcefield types of gas molecules
Atomic charges and van der Waals potentials were then assigned by atom type. These
are listed in Table 3.
σ/Ǻ
3.9150
3.3600
1.0870
3.8400
3.8008
1.4210
4.0530
2.8780
Forcefield Type
c2=
o1=*
h1o
o2*
n1n
h1h
c40
h1
ε / kcal mol-1
0.0680
0.0670
0.0080
0.0800
0.0598
0.0216
0.0700
0.0230
Charge
0.670
-0.335
-0.66
0.330
0.000
0.000
-0.212
0.053
Table 3: Gas nonbonding potential parameters
Bond length energies were modelled with a quartic function of the form
𝑉 = 𝑘2 (𝑟 − 𝑟0 )2 + 𝑘3 (𝑟 − 𝑟0 )3 + 𝑘4 (𝑟 − 𝑟0 )4
(1)
The parameters, in angstroms and kcal/mol for each bond are given in Table 4.
Type I
o1=*
h1o
n1n
h1h
c40
Type J
c2=
o2*
n1n
h1h
h1
r0
1.1600
0.9570
1.0977
0.7412
1.1010
k2
1161.3421
553.2800
1651.3730
414.2185
345.0000
k3
-2564.5706
-1278.9600
-4069.3178
-805.6549
-691.8900
k4
3932.8735
1788.6820
5984.9629
914.1296
844.6000
Table 4: Gas bond potential parameters
Bond angle energies were modelled with a quartic function of the form
𝑉 = 𝑘2 (𝜃 − 𝜃0 )2 + 𝑘3 (𝜃 − 𝜃0 )3 + 𝑘4 (𝜃 − 𝜃0 )4
(2)
The parameters, in degrees and kcal/mol for each gas angle is given in Table 5.
Type I
o1=*
h1o
h1
Type J
c2=
o2*
c40
Type K
o1=*
h1o
h1
θ0
180.00
104.5200
107.6600
k2
57.1000
46.6500
39.6410
k3
0.0000
-11.7046
-12.9210
k4
0.0000
-8.7911
-2.4318
Table 5: Gas angle potential Parameters
To increase the accuracy of the forcefield bond-bond, bond-angle and angle-angle
terms were also included for some gases. These are of the general form
𝑉𝑏𝑜𝑛𝑑−𝑏𝑜𝑛𝑑 = 𝑘𝑏𝑏 (𝑟1 − 𝑟0,1 )(𝑟2 − 𝑟0,2 )
(3)
𝑉𝑏𝑜𝑛𝑑−𝑎𝑛𝑔𝑙𝑒 = 𝑘𝑏𝑎 (𝑟 − 𝑟0 )(𝜃 − 𝜃0 )
(4)
𝑉𝑎𝑛𝑔𝑙𝑒−𝑎𝑛𝑔𝑙𝑒 = 𝑘𝑎𝑎 (𝜃1 − 𝜃0,1 )(𝜃2 − 𝜃0,2 )
(5)
The relevant parameters, in angstroms degrees and kcal/mol are listed in Table 6
Type I
o1=*
h1o
h1
Type J
c2=
o2*
c40
Type K
o1=*
h1o
h1
kbb
275.435
-10.932
5.331
kba
23.8488
18.1030
kaa
-0.3157
Table 6: Gas bond and angle cross-terms
Frameworks
Types were assigned to different atoms following the general type assigning rules in
Compass. Types for boron and scandium were added in from the Dreiding and
Universal forcefields. Table 7 lists the nonbonding types used, the types of atoms
they were used to represent and the van der Waals parameters for that atom type.
Forcefield
Type
b3
o2
c44
c3a
h1
cu+2
o1c3-
Atom
Description
B
O
C
C
H
Cu
O
C
o_v
O
v3o
o_m
zn2o
sc+3
o12
V
O
Zn
Sc
O
n3o
N
n2a
cl1
zn+2
c4
N
Cl
Zn
C
n3
N
Boron in COF-102
Oxygen in COF-102
sp3 carbon with 4 heavy atoms
Aromatic carbon
Generic hydrogen
Copper 2+ ion
Carboxylate oxygen
Carboxylate carbon
Oxygen interacting with
vanadium in MIL-47
Vanadium oxide in MIL-47
Oxygen in Zn4O clusters
Zinc in Zn4O clusters
Scandium in Sc-MOF
Oxygen in nitro group in ZIF-69
Nitrogen in nitro group in ZIF69
Aromatic nitrogen
Chlorine in ZIF-69
Zinc ion
sp3 carbon in Zn2(BDC)2(TED)
Tertiary amine in
Zn2(BDC)2(TED)
σ/Ǻ
ε / kcal mol-1
4.0200
3.3000
3.8540
3.9150
2.8780
2.6500
3.3000
3.9000
0.0950
0.08000
0.02000
0.06800
0.02300
0.04500
0.05000
0.07000
3.6270
0.38280
3.5000
3.6270
3.9800
3.2950
3.4000
0.41278
0.07841
0.54423
0.01900
0.04800
3.7600
0.04800
3.5290
3.8230
2.7000
3.8540
0.09600
0.28600
0.04700
0.06200
3.7200
0.07500
Table 7: Atom types and nonbonding potentials for framework atoms