66 Final R indices

2.3 crystalized in the triclinic crystal system. Ligand 2.3 is symmetric in structure just

2.3 is not planar due to the stacking interaction between the

°. This effect is also observed on the analogue 2.2 where its xanthene

°. The bond lengths P1-C1, P1-C8, P2-C37

2.2 which is 1.83 Å. The angles between the sets of phenyl rings are very close

2.2 which were 101.2 °. Addition of the methyl

2.2. Table 3.11 shows selected bond lengths as well as the

Bond Lengths [Å and °]

P1—C15 P1–P2

Bond Angles

C8—P1—C1

2.12 shows a tetrahedral geometry around the Co ion in a highly

2.3 shows that only little adjustment is

2.3 is 4.168 Å, while in a

°. The P1—Co—P2 angle is

2.2, has showed that these xanthene – based ligands can be

2.2 ligand, bearing in mind a knowledge that the bite

Bond lengths Complex 2.12/

[Å and °]

Complex 2.17/

[Å and °]

P1-C30 P1-C37 P2–C16 P2-C23 / C9 P1—Ni / Co

P2—Ni / Co

Cl(1)—Ni / Co

Cl(2)—Ni / Co

Bond Angles

Cl(2)—Ni/Co—Cl(1)

P(1)—Ni/Co—P(2)

Cl(2)—Ni/Co—P(1) 101.69(3) 108.62(2)

Cl(1)—Ni/Co—P(1) 110.89(3) 99.58(2)

Cl(2)—Ni/Co—P(2) 108.75(3) 102.95(2)

Cl(1)—Ni/Co—P(2) 105.87(3) 107.39(2)

3.3 Summary

[I>2sigma(I)]

R1 = 0.0349, wR2 = 0.0904

R1 = 0.0488, wR2 = 0.1178

R1 = 0.0327, wR2 = 0.0786

R indices (all data) R1 = 0.0398, wR2 = 0.0938

R1 = 0.0563, wR2 = 0.1225

R1 = 0.0512, wR2 = 0.0878

An ORTEP representation of ligand 2.3 is shown in Figure 3.6. The colourless single crystal of ligand

phenyl rings of the diphenylphosphine which makes it dihedral angle between the two phenyl rings to be 166.12

backbone is also not planar with a dihedral angle of 166 °. Xanthene backbone that are planar like that of xantham (4,5-(bis-(di(4-diethylaminomethylphenyl)phosphino)-9,9- dimethylxanthene) have a dihedral angle of 175.6

and P2-C30, which holds the tolyl groups are all at similar distance of about 1.84 Å to that of its analogue

showing that the ligand is symmetric in its structure with C8—P1—C1 101.56 ° and C37—P2—

C30 101.09 ° matching those of its analogue

groups to the phenyl rings was seen to have minor effect, as the bond lengths changed slightly in

comparison to its analogue ligand

bond angles of ligand 2.3.

67

Figure 3.6: ORTEP diagram of ligand 2.3 showing the atom numbering scheme. Thermal ellipsoids are represented at the 50% probability levels.

Table 3.11: Selected bond lengths and bond angles of ligand 2.3.

1.8413(16)

1.8395(16)

1.8351(16)

1.8390(17)

1.8464(16)

1.8402(16) 4.168

101.56(7)

68

symmetrical molecular unit. The structure of ligand

required to form a chelate. The P-P distance in the free ligand

chelation with a P-Co-P (2.12) it P-P distance is 3.973 Å. The P atoms are brought together by means of a decrease of the angle between the phenyl planes in the backbone of the ligand

from 4.168 to 3.973 Å. The angles between the two sets of phenyl rings (C37—P1—C30) and(

C16—P2—C23) are found to be similar with an angle of 105.94

found to be 111.76 °. To complete the tetrahedral geometry, the other two sites are occupied by

two chlorides with a Cl—Co—Cl angle of 117.98 °. These show some distortion, as the angle is

greater than 109 ° for a perfect tetrahedron, however, this is due to the lone-pair repulsion

between the chlorine atoms [23]. The molecular structure also shows that the xanthene-based

ligand is bound to the cobalt in a bidentate fashion via the phosphorus donor atoms. An

analogue of this ligand, xantphos

pincers by using the central oxygen to also bind to a metal [3]. This is explained by the

flexibility range which is calculated to be between 97 and 133 °. A number of studies have

reported xanthene-based ligands of the xantphos type to behave as pincer ligands. The natural

bite angle of xantphos has been determined as 111 ° [3]. There are other factors that also

contribute towards the geometry of the

angle preferred by the metal, is as a result of electronic effects. Therefore, parameters such as

the type of ligands surrounding the metal complex, the charge and the type of metal play a role in

determining whether the ligand will act as a bidentate or a pincer type ligand [24, 25]. An

example, where

was reported as a pincer ligand, is the complex [Rh(xantphos)(COMe)I

]

[26].

69

Figure 3.7: ORTEP diagram of complex 2.12 showing the atom numbering scheme. Thermal ellipsoids are represented at the 50% probability levels.

Ni—P(2), was found to be 108.40 ° and to complete the tetrahedral geometry the other two sites

are occupied by the two chloride ions with a Cl-Ni-Cl angle of 128.87 °. It was observed that the

chlorides are distorted due to the lone pair repulsion between the two chlorine atoms. The

structure also shows that the xanthene-based ligand is coordinated to the nickel in a bidentate

fashion via the two phosphorus donor atoms [26].

70

Figure 3.8: ORTEP diagram of complex 2.17 showing the atom numbering scheme. Thermal

ellipsoids are represented at the 50% probability levels.

71

Table 3.12: Selected bond lengths and bond angles for complex 2.12 and 2.17.

1.813(3) 1.805(3) 1.816(3) 1.808(3) 2.3940(7)

1.8109(18) 1.8191(18) 1.8193(17) 1.8091(18)

2.3398(5)

2.4050(8) 2.3469(5)

2.2213(8) 2.2048(5)

2.2248(7) 2.1964(6)

117.98(3) 128.87(3)

111.76(3) 108.403(18)

The preparation of five cobalt and five nickel complexes with xanthene-based ligands was

achieved. Due to their paramagnetic nature, NMR was found to be unsuitable for structural

characterization. However, they were characterized by elemental analysis, IR, melting point and

single crystal X-ray diffraction.

72