Abstract

A family of mono-, di- and multitopic hydroxamic acids have been employed in the synthesis, structural and physical characterisation of discrete (0-D) and (1- and 2-D) extended network coordination complexes. The majority of the complexes in this thesis have been synthesized using the ligands 2-methoxyphenylhydroxamic acid (L1H2), 4-amino-2-(acetoxy)phenyl hydroxamic acid (L2H2) and 2-(methylamino)phenyl hydroxamic acid (L4H2). More specifically, chapter 2 describes the synthesis and physical characterisation of the monomeric complexes [Cu(II)(L1H)2] (1) and [Ni(II)(L1H)(H2O)(py)3](NO3).MeCN (5) along with the dinuclear ferric complex [Fe(III)2(L1H)4Cl2].2MeCN (2) and the heterovalent heptanuclear complex [Co(III)Co(II)6(L1H)8(L1)2(MeOH)4(NO3)2]NO3·3.5H2O.14MeOH (3). We also present the novel 1-D Zn(II) coordination polymer [Zn(II)2(L1H)2(H2O)5](NO3)2]n (6), also constructed with bridging 2-methoxyphenylhydroxamate ligands. Very recent investigations into the coordinating ability of L1H2 with Ln(III) ions gave rise to the dinuclear complexes [Dy(III)2(L1H)2(H2O)4(NO3)4] (13) and [Gd(III)2(L1H)2(H2O)4(NO3)4] (14) and are described in Chapter 4.

The introduction of an -NH2 group at the 4th position of ligand L1H2 gives rise to the multitopic ligand 4-amino-2-(acetoxy)phenylhydroxamic acid (L2H2). Cu(II) ligation of this organic moiety leads to the 2-D extended network {[Cu(II)(L2H)(H2O)(NO3)]·H2O}n (7), with a [4,4]-net topology. Complexes 1-3 and 5-7 represent extremely rare examples of metal coordination of L1H2 and L2H2 and were therefore recently published in the RSC journal Dalton Transactions.1
We proceeded to replace the -OMe group at the 2-position in L1H2 with a methylamino (-NHMe) moiety, resulting in the synthesis of target ligand 2-(methylamino)phenyl hydroxamic acid (L4H2). This ligand was subsequently successfully incorporated into the pentanuclear MC-4Cu(II) metallacrown [Cu(II)5(L4)4(NO3)2].3H2O (8) and the 1-D coordination polymer {[Zn(II)(L4H)2]·2MeOH}n (9). In solution, the coordination polymer 9 exhibits a solvent dependent photoluminescent emission in the blue region (λPL ≈ 421 – 433 nm) depending on the solvent. In the solid state, a bathochromic shift of ≈ 15 – 30 nm is observed, underlying the importance of inter-chain interactions on the excited state of the complex.

Chapter 3 described the design and synthesis of the more elaborate (and novel) multitopic hydroxamic acids: N-hydroxy-2-[(2-hydroxy-3-methoxybenzyl)amino]benzamide (L5H3), N-hydroxy-4-((2-hydroxy-3-methoxybenzyl)amino)benzamide (L6H3) and N-hydroxy-4-((2-hydroxybenzyl)amino)benzamide (L7H3). The latter two ligands were then successfully combined with Cu(II) nodes to form the unprecedented 1-D coordination polymers: [Cu(II)(L6H2)2]n (11) and {[Cu(II)(L7H2)].2MeOH}n (12). Interestingly, slight differences in the structures of L6H3 and L7H3 lead to significant connectivity and topology changes upon Cu(II) metalation. Complexes 11 and 12 will form the basis of a journal publication in the very near future.
The ligand L5H3 was produced via a one pot Schiff base reduction using sodium triacetoxyborohydride. The introduction of a phenolic moiety at the 2-position of the phenylhydroxamic acid framework deliberately forced non-planarity on the ligand topology. Upon Cu(II) metalation, the 12-MC-4Cu(II) metallacrown [Cu(II)5(L5H)4(MeOH)2](NO3)2.4MeOH.4H2O (10) was produced and represented the first complex to be constructed with such a ligand. Variable temperature magnetic susceptibility measurements on 10 indicates dominant antiferromagnetic exchange.

1. M. B. Fugu, R. J. Ellaby, H. M. O’Connor, M. Pitak, W. Klooster, P. N. Horton, S. J. Coles, M. H. Al-mashhadani, I. F. Perepichka, E. K. Brechin and L. F. Jones. Dalton Trans., 2019, DOI 10.1039/C9DT01531K.