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Title: Novel di- and multitopic hydroxamate ligands towards discrete and extended network complexes
Author: Mohammed, Baba Fugu
ISNI:       0000 0004 7972 6014
Awarding Body: Bangor University
Current Institution: Bangor University
Date of Award: 2019
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Monotopic ; ditopic ; hydroxamate ; hydroxamic acid ; extented network ; Chemistry