Crystal Engineering Of Lanthanide-Transition-Metal Coordination Polymers

A variety of new crystals have been explored through molecular design strategies in view of their significance in the fields of fundamental and applied research. Crystal engineering involves the behavior of molecules or chemical groups in crystals, the crystal design, the control of structures and properties, and the prediction of crystal structures. It is an important approach for the fabrication of functional materials from molecules, with the help of which metal-organic coordination polymers has become a paradigm for the design of new supramolecular structures and the control of their properties. To date, the homometallic transition-metal or lanthanide coordination polymers have been widely studied. In contrast, the analogous chemistry of lanthanide-transition-metal (Ln-M) heterometals remains underdeveloped. The transition-metal ions and lanthanide ions exhibit weak selectivities under complicated coordination conditions, partially leading to homometallic complexes due to the competitive reaction between two different types of metal ions with organic ligands. Therefore, it remains a challenge for the chemists and crystallographers to select and design suitable building units and assemble them into the Ln-M coordination polymer with predictive structure and function.Three strategies including surface modification, enhanced dimension of heterometallic building unit, and ligand-directed assembly have been proposed for the study of the structures, properties and assembly principles of novel Ln-M coordination polymers. The detailed contents are listed as following:â… . Nine transition-metal and lanthanide coordination polymers have been studied by using 3-amino-1,2,4-triazole-5-carboxylate, 3,4-pyridinedicarboxylate, 1,4-benzenedicarboxylate, isonicotinate and nitrate as organic ligands.a) On the basis of bridging ligands containing carboxylate groups, two homometallic zinc coordination polymers, two Zn-Cu coordination polymers and two homometallic lanthanide coordination polymers have been synthesized. One 3D Zn-Cu coordination polymer is assembled from 2D zinc-oxygen layers and 1D copper-iodine chains, and the other is assembled from Zn-Cu-Ligand layers.b) By using nitrate as surface modification ligand, the largest hexacosanuclear lanthanide complex has been rationally synthesized, which, subsequently, has been employed to build up two supra-large tetramers. The tetramer consisting of {Dy₂₆} and {Dy₄} has been found to exhibit the slow relaxation of magnetization.â…¡. Nine chiral or achiral Ln-Ag coordination polymers have been studied by using isonicotinate as bridging ligand and carboxylate species as auxiliary ligand.a) Two homochiral heterometallic coordination polymers have been assembled from 1D inorganic helicates induced by silver ions as chiral units and coordination bonds beween isonicotinate and two different types of metal ions as homochiral interactions.b) Seven achiral heterometallic coordination polymers consisting of 1D inorganic heterometallic chains or lanthanide-carboxylate units have been obtained via tuning the bridging ligands and the auxiliary ligands. The results show that the coordination polymers constructed from 1D inorganic heterometallic chains by using enhanced dimension strategy exhibit target assembly characteristic and high thermal stability.â…¢. Twenty-six chiral and achiral Ln-Cu coordination polymers have been studied with copper-iodine complexes and lanthanide-oxygen complexes (or lanthanide-carboxylate complexes) with different geometries as bulding units, isonicotinates as directed bridging ligands and carboxylate or sulfonate species as auxiliary ligands.a) A chiral coordination polymer with two-fold interpenetratingα-Po topology has been constructed from tetranuclear lanthanide-oxygen unit and hexanuclear copper-iodine unit on the basis of the spontaneous resolution of achiral isonicotinate ligand. With the exploration of assembly principles, two seven-connected self-penetrating coordination polymers constructed from tetranuclear lanthanide-oxygen unit and hexanuclear copper-iodine unit have been rationally designed and synthesized, which implements the transformation from six-connected topology to seven-connected topology in one homochiral lattice through the nicotinate substitution. Furthermore, on the basis of the diversity of copper-iodine complexes and the thermodynamic stability of cubane lanthanide-oxygen unit, two 12-connected chiral coordination polymers have been rationally built up from nanoscale pentadecanuclear copper-iodine unit and tetranuclear lanthanide-oxygen unit.b) Based on the soft-hard/acid-base principle, various auxiliary ligands, such as acetate, oxalate, glycolate, adipate, 1,2-benzenedicarboxylate and p-toluenesulfonate, have been introduced into the Ln-CuI-Isonicotinate system to modify lanthanide structural motif, and the study on heterometallic coordination polymers has been extended to obtain twenty-one heterometallic polymers belonging to somne other eight types. These polymers are constructed from multinuclear lanthanide-oxygen complexes and 1D copper-iodine chains, 1D lanthanide-oxygen chains and multinuclear copper-iodine complexes, 1D lanthanide-oxygen chains and 1D copper-iodine chains, 2D lanthanide-oxygen layers and 1D copper-iodine chains, multinuclear copper-iodine complexes and 1D lanthanide-carboxylate chains, 1D copper-iodine chains and lanthanide-carboxylate complexes with different dimensions, 2D copper-iodine layers and lanthanide-carboxylate complexes with different dimensions, and multinuclear heterometallic complexes, respectively.In this thesis, transition-metal ions and lanthanide ions selectively bond to multifunctional organic bridging ligands or auxiliary ligands through the donor atoms, thus the chemical properties of two different types of metal ions are effectively identified, from which the building units with specific structures can be formed, leading to the formation of heterometallic coordination polymers with predictive features. The current surface modification strategy, enhanced dimension of heterometallic building unit strategy, ligand-directed assembly strategy, and heterometallic assembly principles can be heuristic in term of the design and synthesis of metal coordination complexes with novel topological architectures and functions.