Βασικός στόχος της παρούσης Διπλωματικής Εργασίας ήταν η μελέτη της κρυσταλλικής μηχανικής μίας σειράς συμπλόκων ενώσεων του CoII με ιμιδαζολικά παράγωγα ως υποκαταστάτες και ειδικότερα με το 2-φαινυλοϊμιδαζόλιο και το 4-φαινυλοϊμιδαζόλιο. Η κρυσταλλική μηχανική μπορεί να θεωρηθεί ως ο κλάδος της υπερμοριακής χημείας στη στερεά κατάσταση. Η υπερμοριακή χημεία (supramolecular chemistry) είναι μία από τις πλέον δημοφιλείς και γρήγορα αναπτυσσόμενες περιοχές της πειραματικής χημείας. Χαρακτηρίζεται ως η χημεία των ασθενών διαμοριακών δυνάμεων και εστιάζει στη δομή και λειτουργία των χημικών συστημάτων με υψηλή πολυπλοκότητα (υπερμόρια) που προκύπτουν από το συνδυασμό δύο ή περισσοτέρων διακριτών χημικών ειδών (μορίων, ιόντων) και συγκρατούνται με ασθενείς (και αντιστρεπτές) διαμοριακές δυνάμεις (π.χ. αλληλεπιδράσεις π-π, δεσμούς υδρογόνου, υδρόφοβες αλληλεπιδράσεις, δυνάμεις van der Waals, αλληλεπιδράσεις διπόλου-διπόλου κλπ). Ένα σημαντικό πεδίο της υπερμοριακής χημείας είναι αυτό της κρυσταλλικής μηχανικής (crystal engineering) που αναφέρεται στη στρατηγική σχεδιασμού ενός κρυσταλλικού υλικού με επιθυμητές ιδιότητες και βασίζεται στην κατανόηση και τον έλεγχο των διαμοριακών αλληλεπιδράσεων των μορίων στην κρυσταλλική κατάσταση. Στην παρούσα Διπλωματική Εργασία πραγματοποιήθηκε η σύνθεση συμπλόκων ενώσεων με γενικό τύπο ΜΙΙ/Χ-/L ή L', όπου ΜΙΙ = CoII, X- = Cl-, I-, SCN-, NO3-, L = 2-φαινυλοϊμιδαζόλιο και L' = 4-φαινυλοϊμιδαζόλιο. Με μεταβολή των σημαντικότερων συνθετικών παραμέτρων –γραμμομοριακή αναλογία μετάλλου:υποκαταστάτη, πολικότητα του διαλύτη (MeOH, MeCN, Me2CO, CH2Cl2, CHCl3), συνθήκες θερμοκρασίας και μέθοδο κρυστάλλωσης– απομονώσαμε και χαρακτηρίσαμε τα εξής σύμπλοκα: [CoCl2L2] (1), [CoI2L2] (2), [Co(NCS)2L2] (3), [Co(NO3)2L2] (4), [CoL'4(MeCN)(H2O)](NO3)2 (5), [CoL'4(MeCN)(H2O)]I2 (6), [Co(NCS)2L'2] (7), [Co(NCS)2L'4]•MeOH (8•MeOH). Όπως διαπιστώθηκε με την βοήθεια της κρυσταλλογραφικής ανάλυσης ακτίνων Χ επί μονοκρυστάλλων των ανωτέρω συμπλόκων, οι διαμοριακές αλληλεπιδράσεις που είναι υπεύθυνες για την υπερμοριακή οργάνωση των δομών τους είναι ισχυροί και ασθενείς δεσμοί υδρογόνου και αλληλεπιδράσεις τύπου π-π. Ειδικότερα, τα δεδομένα για τα σύμπλοκα με τον L διαπιστώθηκε ότι: • Σταθερά μοτίβα διαμοριακών αλληλεπιδράσεων (συνθόνια) σχηματίζονται μεταξύ των τεκτονίων N-H των ιμιδαζολικών δακτυλίων και των ενταγμένων ιόντων X (X = Cl, I, NO3, SCN) όλων των συμπλόκων οδηγώντας σε μονο- ή δισδιάστατες δομές. Οι δομές αυτές ενισχύονται περαιτέρω από ασθενείς αλληλεπιδράσεις C-H∙∙∙X (X= Cl, I, O, S) προς 3D υπερμοριακές δομές. • Εκτός του συμπλόκου 2 στο οποίο παρατηρούνται ενδομοριακές π-π αλληλεπιδράσεις σε καμία άλλη δομή δεν παρατηρούνται τέτοιες ενδο- ή διαμοριακές αλληλεπιδράσεις. Για τα σύμπλοκα με τον υποκαταστάτη L' διαπιστώθηκε παρόμοια ότι: • Σταθερά μοτίβα διαμοριακών αλληλεπιδράσεων (συνθόνια) σχηματίζονται μεταξύ των τεκτονίων N-H των ιμιδαζολικών δακτυλίων και των ανόργανων ανιόντων X- (X- = NO3-, I-) στα σύμπλοκα 5 και 6 ή του ενταγμένου SCN στα σύμπλοκα 7 και 8•MeOH ή/και πλεγματικών μορίων διαλύτη (σύμπλοκο 8•MeOH), οδηγώντας σε μονο- ή δισδιάστατες δομές. Παρόμοια με τις δομές 1-4, ασθενείς C-H∙∙∙X (X= O, S) αλληλεπιδράσεις οδηγούν τελικά σε συγκρότηση 3D δομών. • Στα σύμπλοκα 7 και 8•MeOH η οργάνωση της δομής ευνοεί παράλληλα το σχηματισμό διαμοριακών π-π αλληλεπιδράσεων. • Στα σύμπλοκα 5 και 6 είναι απαραίτητη η παρουσία αντισταθμιστικών ιόντων στο πλέγμα τους καθώς πρόκειται για κατιοντικά σύμπλοκα του τύπου [CoL'4(MeCN)(H2O)]2+. • Μόνο το σύμπλοκο 8•MeOH περιέχει πλεγματικά μόρια διαλύτη (MeOH) χωρίς να είναι απαραίτητη η παρουσία αντισταθμιστικών ιόντων στο πλέγμα του. Συμπερασματικά, ο κυρίαρχος παράγοντας που καθορίζει την υπερμοριακή οργάνωση των συμπλόκων και των δύο κατηγοριών (δηλ. με υποκαταστάτες τα ισομερή, 2- και 4-φαινυλοϊμιδαζόλιο) είναι τα ισχυρά συνθόνια N-H∙∙∙X (X = Cl, I, NO3, SCN). / The main target of this diploma thesis was the crystal engineering studies of a series of coordination compounds of CoII with substituted imidazoles as ligands and specifically, with 2-phenylimidazole and 4-phenylimidazole. Crystal engineering may be regarded as the solid-state branch of supramolecular chemistry. Supramolecular chemistry is one of the most popular and rapidly developing areas of experimental chemistry. It may be defined as the chemistry of weak intermolecular forces and focuses on the structure and function of chemical systems of high complexity (supermolecules), resulting from the association of two or more discrete chemical species (molecules, ions) held together by weak (and reversible) intermolecular forces (e.g. π-π interactions, hydrogen bonds, hydrophobic interactions, van der Waals forces, dipole-dipole interactions etc). Crystal engineering is an important field of supramolecular chemistry that refers to the design and synthesis of a crystalline material with desired properties, based on the understanding and control of intermolecular interactions in the crystalline state. In this diploma thesis the synthesis of a series of coordination complexes with general formula ΜΙΙ/Χ-/L or L' [ΜΙΙ = CoII, X- = Cl-, I-, SCN-, NO3- and L = 2-phenylimidazole, L' = 4-phenylimidazole] took place. By altering the parameters of synthesis –metal:ligand molar ratio, solvent polarity (MeOH, MeCN, Me2CO, CH2Cl2, CHCl3), temperature, as well as crystallization method– we were able to isolate and study the following complexes: [CoCl2L2] (1), [CoI2L2] (2), [Co(NCS)2L2] (3), [Co(NO3)2L2] (4), [CoL'4(MeCN)(H2O)](NO3)2 (5), [CoL'4(MeCN)(H2O)]I2 (6), [Co(NCS)2L'2] (7), [Co(NCS)2L'4]•MeOH (8•MeOH). As established by the single-crystal X-ray structure determination of the above complexes, the intermolecular interactions responsible for the supramolecular organization of the structures are strong and weak hydrogen bonds, as well as π-π interactions. A detailed study of the complexes with ligand L reveals that: • Supramolecular synthons between the N-H tectons of imidazole rings and the coordinated X ion (X = Cl, I, NO3, SCN) are formed, leading to 1- or 2D structures, which are further enhanced by weak C-H∙∙∙X (X= Cl, I, O, S) interactions, leading to 3D supramolecular architectures. • There are no intra- or intermolecular π-π interactions observed in complexes 1-4, with the exception of one such intramolecular interaction in complex 2. A detailed study of the complexes with ligand L' reveals that: • Supramolecular synthons between the N-H tectons of imidazole rings and the inorganic anions X- (X- = NO3-, I-) of complexes 5 and 6 or the coordinated SCN of complexes 7and 8 or/and lattice solvent molecules (complex 8•MeOH) are formed, leading to 1- or 2D structures, further organized in 3D architectures by means of weak C-H∙∙∙X (X= O, S) interactions. • In certain complexes (7 and 8•MeOH) the disposition of the complexes favors the formation of intermolecular π-π interactions. • In complexes 5 and 6 the presence of counter ions in their crystal structures is necessary since they are cationic complexes with the [CoL'4(MeCN)(H2O)]2+ unit as their structural core. • Only complex 8•MeOH contains lattice solvent molecules (MeOH) without the presence of counter ions in its crystal lattice. In conclusion, the determining factor of the supramolecular organization of the two series of complexes, that is with the isomers 2- and 4-phenylimidazole as ligands, is the presence of the strong synthons N-H∙∙∙X (X = Cl, I, NO3, SCN).

The work highlighted in this dissertation comprises of syntheses and characterizations of coordination driven supramolecular compounds. The synthesized complexes are characterized by IR spectroscopy, multinuclear NMR spectroscopy and single crystal structure determination. Chapter 2: In this chapter we attempted to make a three dimensional self-assembled cage by the reaction between N, N’, N’’- tris(3-pyridyl)trimesic amide a tritopic donor and Pt(II) based 90° ditopic acceptor cis-(dppe)Pt(II)(OTf)2 [dppe = 1,2-bis(diphenylphosphino)ethane]. It resulted in a trigonal bipyramidal structure. The cage was characterized by single crystal XRD and FT-IR spectra. Chapter 3: In this chapter we have reported the synthesis and characterization of two hereby unknown metal containing carboxylic acid ligands containing the Pt-ethynyl moiety. Also we have shown the preparation and structure analysis of a copper containing metal-organic framework incorporating one of the Pt-ethynyl containing carboxylic acid ligand. This has resulted in the formation of a very interesting hetero-metallic MOF which is quite uncommon in literature.

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Metallosupramolecular chemistry involves the construction of nanoscale molecular assemblies by reacting metal atoms with bridging organic ligands. The metal atoms act as a type of molecular ‘glue’ binding together the organic ligands in specific orientations. Thus, appropriate combinations of metal ions and ligands lead to the controlled self-assembly of interesting one-, two- and three-dimensional molecular aggregates. This thesis details the preparation of a range of novel flexible bridging heterocyclic ligands using conventional organic synthesis, and then explores their reactions with a variety of transition metal precursors. By varying the nature of the organic ligand and the transition metal precursor, new and exciting supramolecular topologies and architectures can be formed. A total of forty-eight ligands were synthesised in this work, forty-seven of which are new compounds. The majority of the ligands synthesised were based around commercially available bisphenol cores. All forty-eight of the ligands had nitrogen heterocyclic groups as coordinating units. The ligands discussed in this thesis can be divided into three main sections. The first involves the synthesis and coordination chemistry of two-armed ligands based around the Bisphenol A, Bisphenol Z and Bisphenol AP cores. The second section describes the synthesis and coordination chemistry of the larger Bisphenol P and Bisphenol M based two-armed bridging ligands. The third section describes the synthesis and coordination chemistry of various multi-substituted ligands, including tripodal ligands based around a trisphenol core, four-armed ligands and six-armed ligands. The two-armed bisphenol based ligands proved very successful as synthons in metallosupramolecular chemistry and produced many products with a variety of different metal atoms. The complexes characterised included discrete dimeric products, coordination polymers and a number of helicates, including a dinuclear quadruply-stranded helicate. Multi-armed ligands are topical, because they have multiple coordination sites that are capable of binding and bridging multiple metal atoms. Such coordination can lead to the construction of cage-like species and complicated networks. A series of three-armed ligands based around a trisphenol core were synthesised with the intention to use these to form such species on coordination with appropriate metal salts. Indeed, one of the products of self-assembly was an interesting M₃L₂ cage. Various other multi-armed ligands were also investigated. The ligands and complexes in this thesis were characterised by a variety of structural techniques, such as ¹H NMR, ¹³C NMR, mass spectrometry, elemental analysis and X-ray crystallography when crystals were obtained. The crystal structures of twenty-seven ligands and forty-three complexes are described.

Nature has always remained a constant source of inspiration for chemists for synthesizing natural products, mimicking enzymatic reactions or to construct molecular architectures resembling biological assemblies. With the rapid growth of ‘Supramolecular Chemistry’ along with the advancement of the synthetic methodologies, molecular systems with brand new complexities have been synthesized, alongside the efficacy of weak, reversible non-covalent interactions have also been extensively explored. A number of such forces including hydrogen bonding, solvophobic effect, dynamic covalent interactions and metal-ligand coordination have been exploited to assemble the molecular building blocks and stitch them together to construct discrete ‘self-assembled’ architectures integrated with desired functionalities. Metal-ligand coordination driven self-assembly certainly evolved as one of the most successful approaches for the construction of discrete supramolecular architectures during last two and half decades. The high directionality and reversible nature of certain metal-ligand bonds allow the pre-designing of sophisticated architectures which can be successfully obtained by ‘error corrections’ via a thermodynamically controlled self-assembly process. Numerous aesthetically elegant two dimensional (2D) and three dimensional (3D) metallosupramolecular architectures have been constructed which have been studied for various potential applications including guest encapsulation, catalysis, sensing, optoelectronics, drug delivery, protection of reactive species etc. Construction of such molecular architectures uses symmetric and rigid building blocks which strictly preserves their geometrical coding and thus finally determines the fate of the self-assembly. Pyridyl-based donors have been extensively used due to their well-behaved coordination with transition metal ions. Interestingly, imidazole based donors remained almost unexplored for such purpose mainly due to the rotational flexibility of imidazole moieties owing to the lack of -electron delocalization with the aromatic backbone, which makes pre-designing an architecture extremely difficult. However, this unpredictability can lead to the formation of unprecedented molecular architectures. Furthermore, the conventional rigid ‘acceptors’ used in the ‘directional bonding approach’ always results in the formation of rigid assemblies, which cannot be utilized for the construction of smart molecular machine based applications. In this context, incorporation of restricted rigidity in the building blocks can be a convenient approach to construct versatile and flexible supramolecular architectures. Although flexible donors are quite common in coordination-driven self-assembly, the use of flexible metal acceptor is scarcely Highly symmetric spherical assemblies of square planer Pd(II) and Pt(II) ions are one of the most extensively studied metallosupramolecular architectures owing to their topological similarity with the spherical virus capsids. Unfortunately, none of the reported molecular spheres are soluble in water which restricts their applications in aqueous media. On the other hand, most of the metallosupramolecular architectures cannot be used for redox based applications as the oxidation state of the associated metal ions must be kept unaltered. Although, assemblies constructed mainly by the ferrocene containing acceptors are shown to be exhibiting redox property, the donor inherited redox active metallosupramolecular systems are extremely rare. Discrete 3D metallosupramolecular cages have been extensively studied as synthetic hosts where the hydrophobic pockets have been utilized as safe shelter for reactive species, for catalyzing chemical transformations, tuning electronic and optical properties of guest molecules, as delivery vehicle for drug molecules etc. However, a major drawback of many such 3D cages is associated with their closed-shell topology, where the large cavities are accessible though relatively much smaller apertures which prevent larger guest molecules to enter inside. So, an interesting finding in this field would be to construct molecular hosts with larger apertures. Picric acid (PA) is a strong organic acid and like many other polynitroaromatic compounds, it is a powerful explosive. In addition, it has large scale industrial application for the synthesis of dyes and pharmaceuticals. However, PA has potential health hazards and it is a water pollutant owing to its high aqueous solubility. Thus, the development of selective receptors which can efficiently interact with PA and detect it at very lower concentration is an appealing field of research. Chapter 1 briefly discusses the history of supramolecular chemistry and the concept of ‘self-assembly’ along with the several synthetic methodologies for the construction of discrete supramolecular architectures. It also includes a brief discussion on the various design approaches to construct 2D and 3D molecular architectures by metal-ligand coordination which is followed by an account on some of the important applications of such metallosupramolecular architectures. At the end, a small introduction on the fluorescence-based detection techniques for PA has also been included. Chapter 2A accounts for the exploration of two linearly substituted benzene bisimidazole donors L1 and L2 for coordination-driven self-assembly. L1 and L2 possesses different ‘natural’ donor angles as the imidazole moieties in L2 are twisted heavily with respect to the phenyl plane due to the steric hindrance exerted by the methyl groups. Interestingly, while the self-assembly of L1 with [cis-(tmeda)Pd(NO3)2] (tmeda = N,N,Nꞌ,Nꞌ-tetramethylethane-1,2-diamine) exclusively formed a [3+3] molecular triangle, the self-assembly of L2 yielded a [4+4] molecular square as the major product with the same acceptor. In addition, similar treatment with the analogous Pt(II) acceptor resulted mixtures of [3+3] and [4+4] assemblies in both cases; however, the [3+3] assembly was the major product in case of L2. These contradictory product distributions in case of L2 with analogous Pd(II) and Pt(II) acceptors could be corroborated by the delicate balance between the entropic and enthalpic contributions. Scheme 1. Self-assembly of L1/L2 with [cis-(tmeda)Pd(NO3)2] and [cis-(tmeda)Pt(NO3)2], respectively. Furthermore, the reactions of L1 and L2 with a 0º bisplatinum acceptor, viz. AntPt yielded the expected [2+2] macrocycles (8 and 9), respectively. However, the interesting observations Scheme 2. Self-assemblies of L1 and L2 with the 0º bisplatinum acceptor AntPt. obtained from the variable temperature NMR studies suggested the existence of a mixture of inter-convertible conformational isomeric structures of 9. Chapter 2B describes the synthesis of a novel semi-rigid bisplatinum acceptor bisPt-NO3 based on benzil backbone for the construction of flexible metallamacrocycles. The benzil group was selected due to its unique rotational flexibility along the benzyl C-C bond which can generate a wide range of bite angles to make it compatible with the variety of donors of diverse shapes and sizes. The acceptor was successfully self-assembled with four different bisimidazole donors (L1-L4) to yield corresponding [2+2] metallamacrocycles (M1-M4) which were characterized by multinuclear NMR and ESI-MS spectrometry; and their structures were elucidated by semi-empirical geometry optimizations. Scheme 3. Self-assembly of [2+2] metallamacrocycles M1-M4 by a semi-rigid bisplatinum acceptor bisPt-NO3. Chapter 3 discusses the synthesis of the very first example of a water soluble molecular sphere MC-1 by the self-assembly of square planar Pd(II) ions with a flexible cationic tritopic donor La(NO3)3 containing 4,4-bispyridyl arms. The structural flexibility of La(NO3)3 makes it capable of binding with metal ions in its syn- or anti-conformations which was also experimentally observed in the structures of the three newly synthesized coordination polymers, viz. Ag-CP, Zn-CP and Cd-CP constructed by using La(NO3)3 as (co)ligand. Finally, the 4:3 self-assembly of [La(NO3)3] and Pd(NO3)2 in aqueous media produced the desired M6L8 type Scheme 4. Self-assembly of the water soluble molecular dice MC-1 from the tricationic tritopic donor La(NO3)3. molecular sphere- MC-1, which contain 36+ overall charges. The compound could be easily solubilized in water after isolation as solid by simple stirring at room temperature. Single crystal X-ray diffraction analysis (SCXRD) revealed the ‘dice’-shaped architecture of MC-1 where the eight faces are occupied by the coordinated Pd2+ ions and the bispyridyl arms and the vertices are occupied by mesityl moieties. MC-1 is stable in aqueous media, however disintegrates in DMSO, as observed by variable temperature NMR experiments. In addition, MC-1 also produced ligand inherited redox signals in cyclic voltammetry experiments. Chapter 4 describes the synthesis of a novel non-symmetric tetraimidazole donor L based on carbazole backbone. The complexity of the donor is associated with the allowed free rotation of the imidazole moieties along with the non-symmetric nature of the carbazole backbone which make L a very unusual donor for coordination-driven self-assembly. The crystal structure of L showed that the presence of the N-Me group caused a greater twisting of the nearby imidazole moieties with respect to the other set of imidazole moieties. The self-assembly of L with [cis-(en)Pd(NO3)2] (en = ethane-1,2-diamine) yielded a mixture of M4L8 and M6L12 type self-assembled products, as evidenced from the ESI-MS spectrometry. However, the DOSY NMR spectra of the product showed a single diffusion coefficient for all the peaks, indicating that both type of assemblies have similar size and hence suggested the formation of a tetrafacial barrel and a cubic architecture. A similar self-assembly of L with [cis-(tmeda)Pd(NO3)2] also produced a water soluble product. ESI-MS spectra in this case only confirmed the formation of a M4L8 assembly- MB-1. SCXRD analysis of the coronene encapsulated complex of MB-1 gave more insights on the sophisticated non-symmetric tetrafacial barrel architecture of MB-1 with large Scheme 5. Construction of the water soluble molecular barrel MB-1 by the self-assembly of a non-symmetric tetraimidazole donor L. rectangular apertures. The centrosymmetric molecule can encapsulate two aromatic guest molecules inside its hydrophobic cavity and was found to be efficiently encapsulating polyaromatic hydrocarbons (PAHs) in aqueous media. In addition, MB-1 has been successfully exploited to carry water insoluble perylene molecule inside HeLa cells for fluorescence imaging purpose without showing significant toxicity. L also formed a water insoluble tetrafacial barrel (MB-2) by self-assembly with [cis-(dppf)Pd(OTf)] (dppf=diphenylphosphino ferrocene) which interestingly has a symmetrical architecture, as evidenced from the SCXRD analysis. The formation of the symmetrical barrel is driven by the steric hindrance between the bulky phenyl groups of the nearby dppf moieties. Chapter 5 reports the study of interactions between picric acid (PA) with a few newly synthesized fluorescent imidazolium salts (S1-S3). The fluorescence titration study of the positively charged receptors with PA showed rapid decrease of the corresponding fluorescence intensities upon gradual addition of PA. The Stern-Volmer plots suggested the involvement of both static and dynamic quenching mechanisms which was further supported by fluorescence lifetime measurements, NMR and UV-Vis spectroscopic analyses. The values of the Stern-Volmer constants (Ksv) reflected strong receptor-PA binding. The quenching efficiency calculations in the presence of several other analytes proved that the receptors are highly selective for PA in both aqueous and non-aqueous media. The mode of interactions in solid state was investigated by the crystal structure analysis of the [S1PA] complex. 1H NMR spectra of the same complex indicated strong interaction between the imidazolium moieties of the receptor Scheme 6. The fluorescent imidazolium salts based receptors S1-S3 and the florescence titration plot for S1 with PA. Inset: the solutions of S1 and (S1+PA) in DMSO under UV light. with PA in solution; however, no significant interaction of PA with the anthracene moieties was observed in solution as we well as in the solid state. Also the quenching efficiencies and the Ksv values were correlated with the positive charge(s) present on the receptors with the help of two newly synthesized mono-positive receptors S4 and S5.