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improvement of characterization and analytical techniques allowed aesthetically fas-
cinating structures of great complexity to be revealed. Apparently, the coordination
processes resulted in a single multicomponent product that was formed relatively
easily, and some “magical” properties were often attributed to supramolecular sys-
tems. To rationalize the design of complex assemblies, the empirical laws for obtain-
ing desired polynuclear complexes have been described by many authors. In this
context, the Raymond's attempt to rationalize the designing of linear helicates and
3D structures can be mentioned [4]. Relatively recently, progress in spectroscopic
methods (NMR, ESMS) and other characterization techniques has allowed a reliable
exploration of self-assembly equilibria in solution. All these achievements signifi-
cantly contributed to a better understanding of self-organized systems.
Artificial helicates represent archetypal metallosupramolecular compounds [5],
whose design was inspired by biochemical self-assemblies such as the double-stranded
DNA structure, whereby hydrogen bonding is replaced with coordination bonds. The
helicates are discrete well defined assemblies usually composed of a limited number of
components, that is, one ligand and one metal ion [6]. This simple system is thus ideally
suited for fundamental investigations of supramolecular self-assemblies in order to bet-
ter understand and describe their structure, thermodynamics and the formation mecha-
nism behind. The NMR spectra of helicates are relatively simple due to a high
molecular symmetry. Using specific structural NMR probes [6] in combination with
other spectroscopic techniques allows complex speciation studies to be performed. Not
surprisingly, a number of features controlling self-assembly were discovered with
helicates, which gives them a special importance in a general understanding of self-
organization. This progress is essential: (i) for a precise design of new functional mate-
rials with a bottom-up approach and (ii) for applying efficient predictive strategies to
evaluate the structural and physico-chemical properties of desired compounds before a
time-consuming synthesis [7].
The aim of this chapter is to provide a conceptual overview of basic self-assembly
principles and related problems, which are discussed in order of increasing complex-
ity. The details about physical origins and mathematical treatments can be found by
experienced readers in original papers. A special focus is given to their implementa-
tion in the chemistry of helicates. In the first part, physico-chemical concepts of fun-
damental processes dealing with the formation of metal-ligand bonds and their
supramolecular counterparts will be given for mononuclear coordination compounds.
These principles will be then transposed to supramolecular helicates, highlighting the
specific features accompanying this extension, especially the consideration of intra-
molecular interactions. A separate part is devoted to the description and assessment of
cooperative interactions that may play an important role in the stabilization of self-
assembled edifices. Kinetic factors are discussed in relation to the self-assembly
mechanisms of dinuclear helicates. An overview of tools for assessing cooperativity
in helicates is presented. The development and applications of thermodynamic model-
ling are described in detail in the next section. Finally, possible secondary interactions
that control the structure of metallohelicates (helical conformational folding) are also
qualitatively discussed. Tutorial examples of helical assemblies are given across the
whole chapter. However, these examples are non-exhaustive and are selected only for
illustrating the phenomena in question.
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