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06 Dec 2017

Yuniar Ponco Prananto, 2009
Monash University

Abstract

The objectives of this research are to explore the synthesis and structures of 3-pyrazol-1-yl based ligands, their metal complexes, and their use in the construction of coordination polymers.

The use of poly(3-pyrazol-1-yl)borate ligands (KBp4bz and KTp4bz) led to the construction of discrete metal complexes of [M(Bp4bz)2], where M are Co(II), Zn(II), and Cd(II). For the Co complexes, both distorted and regular tetrahedral metal geometries were observed, while the Zn complex only displayed a regular tetrahedral geometry. The five coordinated complex [Cd(Bp4bz)2(MeOH)]∙EtOH forms a 1D hydrogen bonded chain due to the EtOH included in the crystal lattice. The metal in all complexes was coordinated by two pyrazolyl nitrogens from each Bp4bz ligand, and left the benzonitrile groups uncoordinated.

Metal complexes of [M(Bp4Bz)(Tp4Bz)] where M are Co(II), Ni(II), Cd(II), and Mn(II) were also synthesised. All of the products contain the same metal complex, but are differently solvated, such that methanol is included in the Cd and Mn complexes, while H2O is included in the Co and Ni complexes. Similar to the [M(Bp4bz)2] complexes, the metals in all the complexes are coordinated by two pyrazolyl nitrogens from the Bp4bz ligand and three pyrazolyl nitrogens from the Tp4bz ligand. An agostic bond (BH∙∙∙∙∙M), which is provided from Bp4bz ligand, completes the octahedral geometries of the metal complexes.

A series of new and existing 3-pyrazol-1-yl based ligands which contain two pyrazolyl groups connected by a spacer unit were synthesized and characterised. The pyrazolyl groups also contained further, peripheral coordinating groups, such as pyridyl and benzonitrile. Specifially, the ligands were 3py3pz and 4py3pz ligands with ethane, propane, butane, and ortho-, meta-, para- dimethylbenzene spacer units, and 4bz3pz ligands with ethane, propane, butane, and meta-, para- dimethylbenzene spacer units. Ligands containing a simple 3py3pz and/or 4py3pz group attached to pyridine were also synthesised.

Several new metal complexes and coordination polymers are obtained from a number of these ligands. Numerous metal complexes of the 3py3pz-et ligand were synthesised, namely the 1D chain coordination polymer of [Zn(3py3pz-et)Cl2]n, the 2D hydrogen-bonded sheet of [Fe(3py3pz-et)2(H2O)2(SCN)2], and a series of 1D chain and 2D (4,4) sheet coordination polymers of composition [Co(3py3pzet)2(SCN)2]n∙solvent. These metal complexes display different flexibility of the 3py3pz-et ligand which led to significant differences in the bridging distance (Npy∙∙∙Npy). In the case of [Co(3py3pz-et)2(SCN)2]n, the variety in the coordination frameworks is influenced by the presence of different guest solvent molecules in the crystal lattice. This, and the flexibility of the 3py3pz-et, gives rise to the supramolecular isomers.

Metal complexes containing the asymmetric ligands 3py3pz-PyBr or 4py3pz-PyBr were also obtained. Both ligands yielded a discrete molecular complex of composition [M(SCN)2(MeOH)2(L)2]. Only the Co complex was produced by the former ligand whereas the Ni and Co complexes were yielded by the latter ligand. All of the complexes form 2D hydrogen bonded sheets through OH∙∙∙S interactions and face-to-face π∙∙∙π interactions. The meta-(3py3pz)-metbz ligand produced the discrete molecular complex [Cd(meta-(3py3pz)-metbz)2(SCN)2]∙H2O∙2DMF, in which non covalent interactions involving DMF∙∙∙H2O∙∙∙SCN are displayed.

Coordination polymers of simple and extended 3-pyrazol-1-yl ligands with dicyanamide co-ligands were also obtained. The dca ligand mostly displayed a terminal μ1 coordination mode or a bridging μ1,5 coordination mode, which has been shown previously not to facilitate long range magnetic ordering. For the [M(dca)x(L)y] complexes, where L are simple 3-pyrazol-1-yl based ligands such as 3py3pz, 4py3pz, 4bz3pz, and 4ba3pz, the complexes have the general formula of [M(dca)2(L)2]n, except for 4bzpz, which generates a discrete molecular complex, [M(dca)2(L)2(H2O)2], which is then connected into a 2D sheet through hydrogen bonding. The other complexes are also expanded from 1D coordination polymers to 2D hydrogen-bonded sheets for [M(dca)2(3py3pz)2]n, a 3D hydrogen bonded network for [M(dca)2(4py3pz)2]n, and a 3D interpenetrated hydrogen bonded network for [M(dca)2(4ba3pz)2]n. Furthermore, in the [M(dca)x(L)y] complexes, the simple 3-pyrazol-1-yl ligands only act as terminal ligands. These ligands bond only through the pyridyl groups for 3py3pz and 4py3pz, or the pyrazolyl groups for 4bz3pz and 4ba3pz. The uncoordinated pyrazolyl or benzoic groups did, however, engage in extensive hydrogen bonding.

In contrast to the simple 3-pyrazol-1yl ligands, the extended ligands always bridged between two metal atoms via their pyridyl nitrogens. In total, two metal dicyanamide complexes containing a ligand with ethane as the spacer unit, and two metal dicyanamide complexes containing a ligand with butane as the spacer unit, were successfully characterised. For the ligand with propane as the spacer unit, three metal dicyanamide complexes, which display different ligand flexibilities, were successfully synthesized. However, only one metal dicyanamide complex containing a ligand with a 1,3-dimethylbenzene as the spacer unit was successfully synthesized. No metal dicyanamide complexes were successfully isolated for the benzonitrile derivatives of the extended 3-pyrazol-1-yl ligands.

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