Exploiting Polymorphism Selective Mechanochemical Synthesis, Structures And Properties Of Supramolecular Complexes Based On Second-sphere Coordination

The combination of organic cations with metal anions to synthesize hybrid metal organic structures via second sphere coordination was used in the early 80s. The importance of second sphere coordination has been demonstrated in supramolecular chemistry in recognition phenomena in biological systems, in metal-based anion receptors and catalysis. In the solid-state, second sphere coordination has been studied much less, but recently, gas adsorption, metalions separation, structural rearrangements, and chiral systems have been reported.We report a racemic crystalline form of the organic N,N,N’,N’-tetrabenzyl-trans-1,2-diaminocyclohexane (L), and how racemic polymorphism is also observed in the second sphere adduct [LH]+·[FeCl4]-. Upon self-assembling L with FeC13·6H2O and HC1, [LH]+·[FeC14]-crystallizes as two polymorphs:α-phase (P21/c) andβ-phase(Pna21). Both polymorphs contain R and S enantiomers in the structure, so are racemic. Weak, attractive C-H…Cl and repulsive C-H…H-C supramolecular interactions play important roles in driving the molecules into non-polar and polar packing. In a solid state, β phase is heated. However, when achieving 110℃ a complete phase transformation occurs and only a-phase is present. Solid-state DFT calculations showed that the most stable structure is the thermodynamic a-phase. The structural transformation from the acentric and polar Pna21to the centric P21/c structure is described upon thermal treatment in the solid-state. The selective formation of the β-phase can be obtained by means of liquid assisted grinding (LAG). Moreover, the single crystal second harmonic generation (SHG) behavior for the polar β-phase is reported, which shows significant efficiency compared to that of urea.The organic ligand of N,N,N’,N’-tetrabenzyl-trans-1,2-diaminocyclohexane (L) and other metal complexes react to get [HL]+·[CuCl3]-crystal 1,[HL]+·[HgCl3]- crystal 2,[HL]+·[CdCl3]- crystal 3,[HL]+·[CuBr3]- crystal 4.This article also discussed a series of crystal 1-4 heating experiments to study the thermal stability of the crystal structure. Results have been confirmed by the use of TGA and X- ray powder diffraction.