LA FASE SUPERIOR DE LA SOCIEDAD COMUNISTA

The asymmetric unit of 21 contains a fully deprotonated BTCA ligand, two lithium ions Li(1) and Li(2), a constitutional water molecule and a dimethyl ammonium cation which acts as a charge balancing counterion. In contrast to 18, 19 and 20, the O donor atoms of the BTCA ligand display two different binding modes (Figure 6.12). The O atoms, O(1), O(2) and O(5) all bind to two different Li ions whereas the O donors O(3), O(4) and O(6) only bind to one Li ion. The Li-O bond lengths vary between 1.881(3) Å and 2.287(3) Å. Detailed bond lengths are summarised in Table 6.7.

The lithium ions in 21 are linked via the O donor atoms resulting in a 2D Li-O

network (Figure 6.13). Within the network there are two types of Li ions, Li(1) and Li(2). Li(1) displays a highly distorted tetrahedral coordination geometry with relevant bond angles ranging between 59.47(8)° and 153.84(2)°, whereas Li(2) shows a distorted square pyramidal coordination environment. The bond angles involving Li(2) vary from 94.62(1)° to 149.49(1)° and are summarised in Table 6.8.

Figure 6.12: Representation of the binding mode of the BTCA ligands contained within 21. Li yellow,

163 Table 6.7: Selected bond lengths for 21

Bond Bond Length Bond Bond Length

Li(1)-O(1) 1.965(3) Å Li(2)-O(1) 2.287(3) Å

Li(1)-O(3') 1.923(3) Å Li(2)-O(2) 2.147(3) Å

Li(1)-O(6'') 1.923(3) Å Li(2)-O(4'''') 2.017(3) Å Li(1)-O(2''') 1.881(3) Å Li(2)-O(5''''') 2.004(3) Å

Li(2)-O(5''') 2.076(3) Å

Symmetry transformations used to generate equivalent atoms:

' = 2-x, 2-y, 1-z, '' = 1.5-x, 2-y, 0.5+z , ''' = -0.5+x, y, 1.5-z, '''' = 2.5-x, 2-y, 0.5+z and ''''' = 0.5 +x, y, 1.5-z

The Li ions with distorted square pyramidal coordination geometries, Li(2) and its symmetry equivalents, are linked together through edge sharing interactions generating dimer units. Within the dimer units the Li ions are doubly bridged by two

µ2 carboxylate oxygen atoms, O(5) and its symmetry equivalent. The dimer units are

further involved in corner sharing interactions with the tetrahedral polyhedra of the Li(1) ions. The corner sharing interactions occur through two vertices of the tetrahedra and involve O(1) and O(2). The edge and corning-sharing bridging motifs result in the formation of Li-O sheets that extend in the (101) plane (Figure 6.13). Within the sheet the Li ions are arranged in a connected 20-membered {Li-O-Li} ring motif (Figure 6.14c).

Figure 6.13: a) Polyhedral representation of the 2D Li-O network contained in 21 (C and H atoms

removed for clarity). b) Highly distorted tetrahedral coordination environment of Li(1) c) distorted square

pyramidal coordination environment of Li(2). Li yellow and O red. (' refers to the 2-x, 2-y, 1-z positions, '' refers to the 1.5-x, 2-y, 0.5+z positions, ''' refers to the -0.5+x, y, 1.5-z positions, '''' refers to the 2.5-x, 2-y, 0.5+z positions and ''''' refers to the 0.5 +x, y, 1.5-z positions)

a)

c) b)

164

Figure 6.14: The 2D Li coordination network contained in 21 as viewed along a) the crystallographic b-

axis and b) the crystallographic a-axis. c) The twenty membered ring motif in 21. d) The coordination

network in 21. Li yellow, O red, C black N, blue and H white. b)

c)

d) a)

165 Unlike the previous compounds 18 - 20 the aromatic ligands don’t further link the Li-O sheets. The ligands are contained within the Li-O sheet producing a 2D hybrid inorganic-organic network (Figure 6.14a and b). The aromatic rings of the BTCA ligands in 21 engage in intermolecular π-π staking interactions which occur

along the crystallographic b-axis. The distance between the centroid of the aromatic

planes is 3.638(2) Å.

The 2D Li-O networks are also linked through hydrogen bonding interactions between the constitutional water molecules and the O donor atoms from the BTCA ligands. The H-bonding interactions occur in the direction of the crystallographic b-

axis and pillar the 2D sheets. The resulting void spaces that extend in the direction of the crystallographic a-axis are filled with the dimethyl ammonium counterions

(Figure 6.14d). The O-O distance of the H-bonding interaction in 21 is 2.45 Å.

Table 6.8: Selected bond angles for 21

Bond Angle Bond Angle

O(1)-Li(1)-O(3') 112.61(1)° O(1)-Li(2)-(O5''''') 97.11(1)° O(1)-Li(1)-O(6'') 99.53(1)° O(1)-Li(2)-O(5'') 96.53(1)° O(1)-Li(1)-O(2''') 107.81(1)° O(2)-Li(2)-O(4'''') 99.87(1)° O(3')-Li(1)-O(6'') 93.39(1)° O(2)-Li(2)-O(5''''') 106.14(1)° O(3')-Li(1)-O(2''') 109.46(1)° O(2)-L(i2)-O(5'') 149.49(1)° O(6'')-Li(1)-O(2''') 133.08(2)° O(4'''')-Li(2)-O(5''''') 104.58(1)° O(1)-Li(2)-O(2) 59.47(8)° O(4'''')-Li(2)-O(5'') 96.13(1)° O(1)-Li(2)-O(4'''') 153.84(2)° O(5''''')-Li(2)-O(5'') 94.62(1)°

Symmetry transformations used to generate equivalent atoms:

' = 2-x, 2-y, 1-z, '' = 1.5-x, 2-y, 0.5+z , ''' = -0.5+x, y, 1.5-z, '''' = 2.5-x, 2-y, 0.5+z and ''''' = 0.5 +x, y, 1.5-z

Compound 21 was also analysed by FT-IR spectroscopy. The spectrum reveals the presence of the BTCA ligand through its characteristic asymmetric and symmetric carboxylate stretches at 1611 cm-1 and at 1484 cm-1, respectivly.164 Thecomposition of 21 was also confirmed by microanalysis (CHN).

166 Table 6.9: Crystal data and structure refinement for 21

Identification code 21

Empirical formula Li2C11H11O7N

Formula weight 283.09 g mol-1

Temperature 150(2) K

Wavelength 0.71073 Å

Crystal system Orthorhombic

Space group Pnma

Unit cell dimensions a = 9.9114(7) Å α= 90°

b = 14.6847(10) Å β= 90° c = 13.5500(9) Å γ = 90° Volume 1972.1(2) Å3 Z 8 Density (calculated) 1.731 Mg/m3 Absorption coefficient 0.143 mm-1 F(000) 1024 Crystal size 0.35 x 0.20 x 0.20 mm3 Theta range for data collection 2.05 to 28.32°

Index ranges -9<=h<=13, -18<=k<=19, -18<=l<=18 Reflections collected 14208

Independent reflections 2546 [R(int) = 0.0496] Completeness to theta = 28.32° 99.8 %

Absorption correction None

Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2546 / 0 / 200

Goodness-of-fit on F2 1.052

Final R indices [I>2sigma(I)] R1 = 0.0416, wR2 = 0.1217 R indices (all data) R1 = 0.0479, wR2 = 0.1249 Largest diff. peak and hole 0.461 and -0.698 e.Å-3

167

6.8 Thermal stability and gas sorption properties of 21

Thermogravimetric analysis (TGA) was performed on 21 (Figure 6.15). A freshly filtered sample of 21 was heated to 900 °C in an air atmosphere at a rate of 10 °C min-1.

The composition of 18 remained unchanged until ca. 135 °C. At this

temperature the compound begins to undergo thermal decomposition. A weight loss of ca. 75 % is observed between 135 °C and 260 °C.

To determine the permanent porosity of 21 a freshly filtered sample was firstly degassed at 100 °C for 24 hours and N2 absorption measurements were attempted.

However, the compound appears to decompose during the sample preparation and consistent N2 absorption/desorption isotherms were not obtained.