A kinetic and mechanistic study of dinuclear platinum (II) complexes with bis-(4'-terpyridyl)-a,w-alkyldiol ligands.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.A series of novel Bis 2,2':6',2″-terpyridinyl ligands, linked through a flexible alkyl chain situated at the 4' position, were synthesised and characterised by microanalysis, FTIR, NMR, UV-Visible spectroscopy, and MS-ToF. Single crystals of all the ligands were obtained, of which one has been published, one has been submitted for publication and one is in preparation for publication. These ligands were then coordinated to platinum(II) and characterised, including ¹⁹⁵Pt NMR spectroscopy. A detailed kinetic study involving the substituting the chloride co-ligand with the following nucleophiles thiourea, 1,3-dimethyl-thiourea and 1,1,3,3-tetramethyl-thiourea was conducted using stopped-flow techniques. An associative reaction mechanism was suggested for the pendant ligand substitution and the following trend in reactivity was observed: L2-Ptα > L3-Ptβ > L1-Ptχ. UV-Visible absorption spectra were recorded on sequentially diluted solutions of the ligands (in chloroform), and the platinum complexes (in water). These spectra obeyed the Beer-Lambert law. The values of the molar absorption coefficients at the wavelengths of maximum absorption for the ligands followed the trend L1 < L2 < L3, whilst for the complexes the trend was L1-Pt < L3-Pt < L2-Pt. It has been concluded that at low concentrations L2-Pt and L3-Pt undergo intramolecular folding. Variable temperature and variable concentration NMR spectroscopic studies were performed on all three complexes. At higher complex concentrations intermolecular self-association takes place for L2-Pt and L3-Pt but not for L1-Pt. The reactivity of the complexes is predominately determined by their structural conformations in solution. At low concentrations the L1-Pt complex remains in its linear conformational state, whilst the L2-Pt and L3-Pt complexes undergo intramolecular folding with the formation of an axial Pt—Pt bonded and π—π stacked dinuclear platinum terpyridine centre. The latter is believed to be more active in the substitution reaction than the original mononuclear centre. The reasons for the folding and self-association in the L2-Pt and L3-Pt systems are related to the steric crowding and stress in the spacer region of the folded or self-associated complexes

The dynamics of new self-assembled porous materials

Thesis (PhD)--Stellenbosch University, 2015.ENGLISH ABSTRACT: principal goal of this study was to prepare a wide selection of crystalline second- and third-generation metal-organic materials in order to investigate guest sequestration and storage capabilities, as well as guest exchange and sorption-induced dynamics in the solid state. Chapters I and II contain a review of the relevant literature, as well as a description of the experimental techniques employed in this work. Chapter III describes the diversity of metal-organic frameworks (MOFs) obtained from a small selection of pyridyl-functionalised ligands (varying in length and rigidity) combined with a series of carboxylic acids (also varying in length and rigidity) in the presence of one of four transition metals. Twenty one different MOFs varying in metal coordination mode, degree of interpenetration, solvent-accessible space and guest were obtained. Four of these MOFs undergo single-crystal to single-crystal (SC-SC) transformations, including activation, gas sorption and solvent exchange. Chapter IV focuses on two isostructural MOFs. The monochromic zinc-containing framework undergoes SC-SC guest exchange, indicating a mild preference for para-xylene, while gas sorption experiments revealed a clear preference for carbon dioxide. The pleochroic crystals of the cobalt analogue showed no xylene selectivity, but gas sorption experiments revealed preferential selectivity toward methane carbon dioxide and ethane. Crystallisation from solutions containing both metals (and the same ligands) resulted in the formation of trichroic solid solutions, the colour of which could be fine-tuned by varying the ratio of the two metals. To complete the study, a homoepitaxial crystal was grown. Chapter V focuses on a modified version of the ligand described in Chapter IV, with electron-withdrawing fluorine atoms located on the central phenyl ring. Use of this ligand resulted in charaterisation of a twofold interpenetrated porous framework, differing from that described in the previous chapter. Activation, as well as guest exchange, elicited “crank-handle” conformational changes in the ligand. Sorption experiments showed the material to be selective for carbon dioxide over several linear alkanes. Reaction using the hydrochloride salt of this ligand yielded a novel interdigitated MOF. Substitution of cadmium for zinc in the reaction gave a third non-interpenetrated framework where the ligand has undergone [2 + 2] cycloaddition and is present in the anti conformation. SC-SC activation as well as guest exchange experiments revealed this framework to be less flexible than its zinc counterpart. Exposure of the activated material to carbon dioxide indicated substantial uptake of carbon dioxide. A mixture of the DMF and DMSO produced two additional isoskeletal structures differing in paddlewheel construction, ligand conformation and, as a result, in the solvent-accessible void space. Chapter VI describes the response of five MOFs based on diarylethene ligands to light. The structural changes underlying the colour change differ in each case. The first framework is a porous twofold interpenetrated MOF that undergoes change in colour and shape upon UV irradiation. When the same crystal was exposed to white light, the parameters revert back to those of the original form. The activated form of a second fourfold interpenetrated highly porous MOF showed an affinity for carbon dioxide, as well as a change in colour upon irradiation. Incorporation of a more flexible ligand gave a twofold interpenetrated porous material that showed low temperature activation but could not be evacuated without loss of crystallinity. UV irradiation induced a colour change but no structural change. The fourth framework is a twofold interpenetrated structure that collapses to a seemingly non-porous form upon removal of the solvent. UV irradiation of this material results in ring-closure of the diarylethene ligand, along with a colour change. Remarkably, all these processes occur in a SC-SC fashion. This is the first example of photo-induced ring closure of a diarylethene molecule incorporated into a MOF. The fifth framework exhibits a high degree of interpenetration (fourfold) but unlike all previous examples, irradiation with UV light induced no visible colour change and no structural change.AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om 'n wye verskeidenheid kristallyne tweede- en derde-geslag metaal-organiese materiale voor te berei, om gas sekwestrasie, stoor vermoëns, sowel as gas uitruiling en sorpsie geïnduseerde dinamika in die vaste toestand te bestudeer. Hoofstukke I en II bevat 'n oorsig van die relevante literatuur en 'n beskrywing van die eksperimentele tegnieke in hierdie werk. Hoofstuk III beskryf die verskeidenheid metaal-organiese raamwerke (MOFs) wat gesintetiseer is vanuit 'n klein seleksie piridiel gefunksionaliseerde ligande (met verskillende lengte en rigiditeit) gekombineer met 'n reeks karboksielsure (ook met verskillende lengte en rigiditeit) in die teenwoordigheid van een van vier oorgangsmetale. Een en twintig verskillende MOFs met verskillende metaal koördinasie modusse, graad van interpenetrasie, oplosmiddel toeganklike ruimte en gaste was gesintetiseer. Vier van hierdie MOFs toon enkel-kristal tot enkel-kristal (SC-SC) transformasies, insluitend aktivering, gas sorpsie en die uitruil van hulle oplosmiddel. Hoofstuk IV fokus op twee isostrukturele MOFs. Die monokromiese sink-bevattende raamwerk ondergaan SC-SC gas uitruiling, wat dui op 'n matige voorkeur vir para-xileen, terwyl gas sorpsie eksperimente ‘n duidelike voorkeur vir koolstofdioksied toon. Die pleokroïede kristalle van die kobalt analoog toon geen selektiwiteit teenoor xileen nie, terwyl gas sorpsie eksperimente ‘n voorkeur teenoor metaan etaan en koolstofdioksied vertoon. Kristallisasie van oplossings wat beide metale bevat (asook dieselfde ligande) lei tot die vorming van trikroïede vaste oplossings, en die kleur hiervan kan verander word deur die verhouding van die twee metale te wissel. Om die studie te voltooi, is 'n homoepitaksiale kristal gegroei. Hoofstuk V fokus op 'n aangepaste weergawe van die ligand wat in Hoofstuk IV beskryf is, met elektron-onttrekkende fluooratome wat op die sentrale fenielring geleë is. Gebruik van hierdie ligand het gelei tot die karakterisering van 'n tweevoud geïnterpenetreerde poreuse raamwerk, wat verskil van dit wat in die vorige hoofstuk beskryf is. Aktivering, sowel as gas uitruiling, lok slinger konformasie veranderings in die ligand uit. Sorpsie eksperimente toon aan dat die materiaal koolstofdioksied bo 'n paar lineêre alkane verkies. Reaksie met die chloriedsout van hierdie ligand het ‘n nuwe MOF opgelewer. Vervanging van kadmium met sink in die reaksie lewer 'n derde nie-geïnterpenetreerde raamwerk op, waar die ligand [2 + 2] siklo-addissie ondergaan het en in die anti-konformasie teenwoordig is. SC-SC aktivering, sowel as gas uitruilingseksperimente, het getoon dat hierdie raamwerk minder buigsaam as sy sink eweknie is. Blootstelling van die geaktiveerde materiaal aan koolstofdioksied dui op 'n verstommende opname van koolstofdioksied. Die byvoeging van DMSO tot die DMF oplossing het tot die vorming van nog twee isoskeletale strukture gelei, wat verskil in hul spaanwiel konstruksie, ligand konformasie en, as gevolg hiervan, ook in hul oplosmiddel-toeganklike leë ruimte. Hoofstuk VI beskryf die reaksie van vyf MOFs gebaseer op diarieleteen ligande met lig. Die kleurveranderinge en onderliggende strukturele veranderinge verskil van kristal tot kristal. Die eerste raamwerk is ‘n poreuse tweeledig geïnterpenetreerde MOF, wat 'n dramatiese kleur- en vormverandering tydens UV-bestraling ondergaan. Wanneer dieselfde kristal aan wit lig blootgestel word, keer die selgrense terug na dié van die oorspronklike vorm. Die geaktiveerde vorm van 'n tweede viervoudig geïnterpenetreerde hoogs poreuse MOF het 'n affiniteit vir koolstofdioksied, en toon ook 'n kleurverandering tydens bestraling aan. Die gebruik van 'n meer buigsame ligand het 'n tweevoud geïnterpenetreerde poreuse materiaal opgelewer wat by lae temperatuur geaktiveer word, maar nie ontruim kon word sonder verlies van kristalliniteit nie. Bestraling veroorsaak 'n kleur verandering, maar geen strukturele verandering nie. Die vierde raamwerk is 'n tweeledig geïnterpenetreerde struktuur wat ineenstort en 'n oënskynlik nie-poreuse struktuur vorm wanneer die oplosmiddel verwyder word. Bestraling van hierdie materiaal lei tot ring-sluiting van die diarieleteen ligand, wat met 'n kleurverandering gepaard gaan. Dit is opvallend dat al hierdie prosesse d.m.v. 'n SC-SC transformasie plaasvind. Dit is die eerste voorbeeld van die foto-geïnduseerde ring-sluiting van 'n diarieleteen ligand as deel van 'n MOF. Die vyfde raamwerk toon 'n hoë graad van interpenetrasie (viervoud), maar in teenstelling met al die vorige voorbeelde, veroorsaak bestraling met UV-lig geen sigbare kleurveranderinge en geen strukturele veranderinge nie

Inclusion of a dithiadiazolyl radical in a seemingly non-porous solid

Inclusion of the dithiadiazolyl radical PhCNSSN• into the dynamically porous metallocycle [Cu2(L1)2Cl4], where L1 is the bidentate ligand 1,3-bis(imidazol-1-ylmethyl)-2,4,6- trimethylbenzene, has been achieved by gas phase diffusion. Single crystal X-ray diffraction, powder X-ray diffraction, UV-visible spectroscopy, EPR and SQUID magnetometry studies confirm inclusion of the radical into this seemingly non-porous material, and illustrate the presence of antiferromagnetic coupling between the paramagnetic host and guest species. The radical guest is readily released by heating or by the addition of solvent (CH2Cl2)

1,4-Bis[(2,2′:6′,2′′-terpyridin-4′-yl)­oxy]butane

The title compound, C34H28N6O2, has an inversion centre located at the mid-point of the central C—C bond of the diether bridging unit. The central pyridine rings of the terpyridyl units and the diether chain are co-planar: the maximum deviation from the 18-atom mean plane defined by the bridging unit and the central pyridyl ring is for the pyridyl N atom which sits 0.055 (1) Å above the plane. The dihedral angles between the terminal pyridine rings with this plane are 10.3 (1) and 37.6 (1)°, repectively. In the crystal, weak C—H⋯N inter­actions link the mol­ecules into infinite chains parallel to the a axis

Effect of Extra-Framework Anion Substitution on the Properties of a Chiral Crystalline Sponge

Chiral metal–organic materials, CMOMs, are of interest as they can offer selective binding sites for chiral guests. Such binding sites can enable CMOMs to serve as chiral crystalline sponges (CCSs) to determine molecular structure and/or purify enantiomers. We recently reported on the chiral recognition properties of a homochiral cationic diamondoid, dia, network {[Ni(S-IDEC)(bipy)(H2O)][NO3]}n (S-IDEC = S-indoline-2-carboxylicate, bipy = 4,4′-bipyridine), CMOM-5[NO3]. The modularity of CMOM-5[NO3] means there are five feasible approaches to fine-tune structures and properties via substitution of one or more of the following components: metal cation (Ni2+); bridging ligand (S-IDEC); linker (bipy); extra-framework anion (NO3–); and terminal ligand (H2O). Herein, we report the effect of anion substitution on the CCS properties of CMOM-5[NO3] by preparing and characterizing {[Ni(S-IDEC)(bipy)(H2O)][BF4]}n, CMOM-5[BF4]. The chiral channels in CMOM-5[BF4] enabled it to function as a CCS for determination of the absolute crystal structures of both enantiomers of three chiral compounds: 1-phenyl-1-butanol (1P1B); methyl mandelate (MM); ethyl mandelate (EM). Chiral resolution experiments revealed CMOM-5[BF4] to be highly selective toward the S-isomers of MM and EM with enantiomeric excess, ee, values of 82.6 and 78.4%, respectively. The ee measured for S-EM surpasses the 64.3% exhibited by [DyNaL(H2O)4] 6H2O and far exceeds that of CMOM-5[NO3] (6.0%). Structural studies of the binding sites in CMOM-5[BF4] provide insight into their high enantioselectivity

One Atom Can Make All the Difference: Gas-Induced Phase Transformations in Bisimidazole-Linked Diamondoid Coordination Networks

Coordination networks (CNs) that undergo gas-induced transformation from closed (nonporous) to open (porous) structures are of potential utility in gas storage applications, but their development is hindered by limited control over their switching mechanisms and pressures. In this work, we report two CNs, [Co(bimpy)(bdc)]n (X-dia-4-Co) and [Co(bimbz)(bdc)]n (X-dia-5-Co) (H2bdc = 1,4-benzendicarboxylic acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene), that both undergo transformation from closed to isostructural open phases involving at least a 27% increase in cell volume. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO2, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P0 ≈ 0.008 or P ≈ 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, and modeling (density functional theory calculations, and canonical Monte Carlo simulations) studies provide insights into the nature of the switching mechanisms and enable attribution of pronounced differences in sorption properties to the changed pore chemistry

One Atom Can Make All the Difference: Gas-Induced Phase Transformations in Bisimidazole-Linked Diamondoid Coordination Networks

Coordination networks (CNs) that undergo gas-induced transformation from closed (nonporous) to open (porous) structures are of potential utility in gas storage applications, but their development is hindered by limited control over their switching mechanisms and pressures. In this work, we report two CNs, [Co(bimpy)(bdc)]n (X-dia-4-Co) and [Co(bimbz)(bdc)]n (X-dia-5-Co) (H2bdc = 1,4-benzendicarboxylic acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene), that both undergo transformation from closed to isostructural open phases involving at least a 27% increase in cell volume. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO2, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P0 ≈ 0.008 or P ≈ 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, and modeling (density functional theory calculations, and canonical Monte Carlo simulations) studies provide insights into the nature of the switching mechanisms and enable attribution of pronounced differences in sorption properties to the changed pore chemistry

One Atom Can Make All the Difference: Gas-Induced Phase Transformations in Bisimidazole-Linked Diamondoid Coordination Networks

Coordination networks (CNs) that undergo gas-induced transformation from closed (nonporous) to open (porous) structures are of potential utility in gas storage applications, but their development is hindered by limited control over their switching mechanisms and pressures. In this work, we report two CNs, [Co(bimpy)(bdc)]n (X-dia-4-Co) and [Co(bimbz)(bdc)]n (X-dia-5-Co) (H2bdc = 1,4-benzendicarboxylic acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene), that both undergo transformation from closed to isostructural open phases involving at least a 27% increase in cell volume. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO2, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P0 ≈ 0.008 or P ≈ 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, and modeling (density functional theory calculations, and canonical Monte Carlo simulations) studies provide insights into the nature of the switching mechanisms and enable attribution of pronounced differences in sorption properties to the changed pore chemistry

One Atom Can Make All the Difference: Gas-Induced Phase Transformations in Bisimidazole-Linked Diamondoid Coordination Networks

Coordination networks (CNs) that undergo gas-induced transformation from closed (nonporous) to open (porous) structures are of potential utility in gas storage applications, but their development is hindered by limited control over their switching mechanisms and pressures. In this work, we report two CNs, [Co(bimpy)(bdc)]n (X-dia-4-Co) and [Co(bimbz)(bdc)]n (X-dia-5-Co) (H2bdc = 1,4-benzendicarboxylic acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene), that both undergo transformation from closed to isostructural open phases involving at least a 27% increase in cell volume. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO2, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P0 ≈ 0.008 or P ≈ 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, and modeling (density functional theory calculations, and canonical Monte Carlo simulations) studies provide insights into the nature of the switching mechanisms and enable attribution of pronounced differences in sorption properties to the changed pore chemistry