| Summary: | Thesis (MSc)--Stellenbosch University, 2008. === ENGLISH ABSTRACT: This study comprises the synthesis and full characterization of two novel pendant-arm
donor macrocyclic ligands. The stability and structure of the complexes of these two
ligands with a series of metals ions [Mn(II), Co(II), Zn(II), Cd(II), Pb(II)], was
subsequently investigated.
The two parent macrocyclic ligands, 1,4,7-triazacyclodecane ([10]-ane-N3) and 1,4,8-
triazacycloundecane ([11]-ane-N3) were synthesized by means of the "direct
synthesis" method using tosylates as protecting groups. Pendant arms were then
added to the parent molecules to create hexadentate ligands. The two macrocyclic
ligands are asymmetric because of the different lengths of the carbon bridges between
the N-donor atoms of the rings. This feature gives the ligands the possibility to form
both five- and six-membered rings when coordinated to metal centers. The ligands
were fully characterized by means of NMR, mass spectrometry and elementalanalysis.
Melting points were also determined.
These two novel (triaza macrocyclic) ligands now complete the series between 9-ane-
N3 [with its 2-(S)-hydroxypropyl pendant arms] and 12-ane-N3 [with its 2-(S)-
hydroxypropyl pendant arms].
Protonation data of the ligands were determined using potentiometric titrations. The
respective protonation constants for both ligands in 0.1000 mol dm-3 NaNO3 are:
THTD log H
1 K = 9.176 and log H
2 K = 4.20
THTUD log H
1 K = 11.32 and log H
2 K = 5.87
A third protonation constant for both ligands (THTD and THTUD) was observed, but
the use of potentiometric methods could not produce reliable values at very low pH
values. stability constants of the new ligands with a series of metal ions were determined
using 0.1000 mol dm-3 NaNO3 as ionic medium. The log(K) values at 25°C with
THTD are:
Co(II) 22.93
Zn(II) 14.82
Cd(II) 19.38
Pb(II) 15.47
The log(K) values at 25°C with THTUD are:
Co(II) 17.52
Zn(II) 16.43
Cd(II) 18.05
Pb(II) 14.63
Very stable complexes were obtained with the larger Cd(II) ion when compared to
other similar ligands.
Crystal structures of some of the metal complexes were determined by X-ray
crystallography. Metal perchlorates were used in the preparation of the metal
complexes with THTD and THTUD, and various methods were utilized for the
crystallization process. The general formula for these complexes is [M(L)]2+·2(ClO4)-
where M=metal ion and L= neutral ligand. The bond lengths between the nitrogen
atom and the metal ion, and the oxygen atom and the metal ion are very much the
same in the respective crystal structures. This means that the metal ion lies almost
halfway between the nitrogen and the oxygen atoms. The Mn(II)-THTD complex
featured both a distorted octahedral and distorted trigonal prismatic configuration in
the unit cell. Co(II)-THTUD contains three molecules per unit cell all having a
distorted octahedral configuration. Zn(II)-THTUD crystallizes with six molecules per
unit cell. === AFRIKAANSE OPSOMMING: Hierdie studie behels die bereiding en volledige karakterisering van twee oorspronklike
hangkroonarmdonor makrosikliese ligande. Die stabiliteite en struktuur van komplekse van
hierdie twee ligande met ’n reeks metaalione [Mn(II), Co(II), Zn(II), Cd(II), Pb(II)] is
ondersoek.
Die twee basis ligande 1,4,7-triazasiklodekaan (10-ane-N3) en 1,4,8-triazasikloundekaan (11-
ane-N3) is gesintetiseer deur middel van die "direkte bereidingsmetode" met tosilate as
beskermingsgroepe. Hangkroonsyarms is aangeheg om die vorming van ’n heksadentate
ligand te bewerkstellig. Die twee makrosikliese ligande is asimmetries as gevolg van die
verskillende lengtes van die koolstofbrûe tussen die N-donor atome van die ringe. Hierdie
eienskap gee aan die ligande die vermoë om beide vyf- en seslidringe te vorm wanneer
komplekse gevorm word met metaalione. Die ligande is ten volle gekarakteriseer deur
middel van KMR-metings, massa-spektroskopie en element analise. Smeltpuntbepalings is
ook uitgevoer.
Die twee nuwe ligande voltooi nou die homoloë reeks tussen 9-ane-N3 [en sy 2-(S)-
hidroksiepropiel hangkroonarms] en 12-ane-N3 [en sy 2-(S)-hidroksiepropiel
hangkroonarms].
Protonasiedata van die ligande is bepaal deur middel van potensiometriese titrasie. Die
onderskeie protonasiekonstantes vir beide ligande in 0.1000 mol dm-3 NaNO3 is:
THTD log H
1 K = 9.176 en log H
2 K = 4.20
THTUD log H
1 K = 11.32 en log H
2 K = 5.87
’n Duidelik-waarneembare derde protonasiekonstante vir beide ligande (THTD en THTUD)
is opgemerk, maar potentiometriese metodes kon nie betroubare waardes lewer by die uiters
lae pH-lesings nie. Vormingskonstantes van die ligande met ’n reeks oorgangsmetale is bepaal deur gebruik te
maak van ’n 0.1000 mol dm-3 NaNO3 as ioniese medium. Die log(K) waardes by 25°C vir
THTD is:
Co(II) 22.93
Zn(II) 14.82
Cd(II) 19.38
Pb(II) 15.47
Die log(K) waardes by 25°C met THTUD is:
Co(II) 17.52
Zn(II) 16.43
Cd(II) 18.05
Pb(II) 14.63
Uiters stabiele komplekse is verkry met die groter Cd(II) ioon in vergelyking met ander
soortgelyke ligande.
Kristalstrukture van sommige van die metaalkomplekse is bepaal deur middel van X-straal
kristallografie. Metaalperchlorate is gebruik om metal komplekse met THTD en THTUD te
berei, en ’n verskeidenheid kristallisasieprosesse is gebruik. Die algemene formule vir
hierdie komplekse is [M(L)]2+·2(ClO4)- waar M = metaal ioon en L = neutrale ligand is. Die
bindingslengtes tussen die stikstof atoom en die metaalioon, en die suurstof atoom en die
metaalioon is nagenoeg dieselfde in die onderskeie kristalstukture. Dit beteken dat die
metaalioon ongeveer halfpad tussen die stikstof en die suurstof atome voorkom. Die Mn(II)-
THTD-kompleks vertoon beide oktahedrale - en trigonaal prismatiese konfigurasie in die
eenheidsel. Co(II)-THTUD het drie molekule per eenheidsel, almal verwronge oktahedrale
konformasies. Zn(II)-THTUD het gekristaliseer met ses molekule per eenheidsel.
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