Building on established supramolecular chemistry, metal coordination and organometallic chemistry have been widely explored for supramolecular polymers and nanostructures. Increasingly, research has demonstrated that this approach is promising for the synthesis of novel materials with functions and properties derived from metal elements and their coordination structures. Unique self-assembling behaviour and unexpected supramolecular structures are frequently discovered due to multiple non-covalent interactions in addition to metal coordination. However, an explicit understanding of the synergistic effects of non-covalent interactions for designed synthesis of metal containing assemblies with structure correlated properties remains a challenge to be addressed. Recent literature in the area is highlighted in this review in order to illustrate newly explored concepts and stress the importance of developing well understood and controlled supramolecular chemistry for designed synthesis.

PPh3CpFe(CO)(CO)(CH2)5CH3 (FpC6) spontaneously forms supramolecular polymers in the solid state. The polymers crystallize slowly over a period of one month and can be recovered by melting the crystals at 65 °C. The rheological profile of FpC6 fits the Maxwell model indicating the presence of chain entanglement. Crystal analysis reveals that FpC6 is able to assemble, via cooperative π–π interactions and weak C–H···O hydrogen bonding, into a duplex chain structure with truss arrangement of iron atoms. Powder X-ray diffraction (PXRD) of the polymers shows a double-peak pattern, characteristic for duplex ladder polymers. FTIR/ATR analysis further supports that carbonyl groups are involved in C–H···O hydrogen bonding responsible for the self-assembly. This discovery opens up new design motifs for organometallic supramolecular polymers.

The effect of chain structure on flexibility and stability of macromolecules containing weak P-Fe metal coordination bonds is studied. Migration insertion polymerization (MIP) of FpC Fp (1) and PR C PR (2) (Fp: CpFe(CO) ; C and C : alkyl spacers; P: phosphine; R: phenyl or isopropyl) generates P(1/2), in which the P-Fe and Fe-P bonds with opposite bonding direction are alternatively arranged in the backbone. On the other hand, P(FpC P) synthesized from AB-type monomers (FpC P) has P-Fe bonds arranged in the same direction. P(1/2) is more rigid and stable than P(FpC P), which is attributed to the chain conformation resulting from the P-Fe bonding direction. In addition, the longer spacers render P(1/2) relatively flexible; the phenyl substituents, as compared with the isopropyl groups, improves the rigidity, thermal, and solution stability of P(1/2). It is therefore possible to incorporate weak metal coordination bonds into macromolecules with improved stability and adjustable flexibility for material processing.

Frequently encountered in crystalline materials, aromatic embraces (AEs) are formed when arylated molecules interact through multiple concerted aromatic interactions. AEs are ar obustm otif that is suitable for the preparation of amorphous bulk supramolecular polymers( BSPs).C rystal engineering revealed thatt he polymorphicc ompound (PPh 3 )(Cp)Fe(CO){CO(CH 2 ) 5 CH 3 }( Cp = cyclopentadienyl), known as FpC 6 ,a ssembled into variousc hain structures through severalA Em otifs. Upon melting, FpC 6 always adopted the same AE motif, whiche xtended into the corre-spondinge mbracing "ladder" chains. The resultant BSP displayedt ypical polymer behaviour,i ncluding the presence of ag lass transition and viscoelasticity,w hich allowed the effect of thermalh istory on the polymerisation behaviour to be explored.T he ladderc hains formed by the AE remain assembled at temperatures of up to 130 8Ca nd were able to effectively suppress crystallisation during cooling. The ability of the AE to form chains at high temperatures and suppress crystallisation is an ew opportunity to advance the field of BSPs and supramolecular chemistry.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.

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