Catalysis of an Aldol Condensation Using a Coordination Cage

The aldol condensation of indane-1,3-dione (ID) to give ‘bindone’ in water is catalysed by an M8L12 cubic coordination cage (Hw). The absolute rate of reaction is slow under weakly acidic conditions (pH 3–4), but in the absence of a catalyst it is undetectable. In water, the binding constant of ID in the cavity of Hw is ca. 2.4 (±1.2) × 103 M−1, giving a ∆G for the binding of −19.3 (±1.2) kJ mol−1. The crystal structure of the complex revealed the presence of two molecules of the guest ID stacked inside the cavity, giving a packing coefficient of 74% as well as another molecule hydrogen-bonded to the cage’s exterior surface. We suggest that the catalysis occurs due to the stabilisation of the enolate anion of ID by the 16+ surface of the cage, which also attracts molecules of neutral ID to the surface because of its hydrophobicity. The cage, therefore, brings together neutral ID and its enolate anion via two different interactions to catalyse the reaction, which—as the control experiments show—occurs at the exterior surface of the cage and not inside the cage cavity.

The Packing Coefficient of Particles in Structure Cluster Systems

Within the framework of the cluster model, a relation is obtained for calculating the effective diameter of particles and the atomic packing coefficient in the cluster structure, which makes it possible to trace the dependence of the effective particle diameter on the temperature and the quantitative composition of the cluster system. The results of calculating the diameter of particles in a cluster model and classical models of hard and soft spheres are compared. The greatest discrepancy between the predicted particle diameters and the packing coefficients in the cluster structure within the framework of various models is observed near the melting point of the substance, where the difference can reach 16%.

2-Methylresorcinarene: a very high packing coefficient in a mono-anion based dimeric capsule and the X-ray crystal structure of the tetra-anion

Mono- and tetra-deprotonated 2-methylresorcinarene anions (1 and 2) as their trans-1,4-diammoniumcyclohexane (TDAC)2+ inclusion complexes are reported.

trans-Tetraamminebis(hydrogensulfito)ruthenium(II), trans-[Ru(SO3H)2(NH3)4], a Structure with an Unexpected Rod Packing

trans-[Ru(SO3H)2(NH3)4], monoclinic, space group P21/n, Z =2, a = 619.4(3), b = 701.8(3), c = 1068.6(6) pm, β = 96.32(3)°. In the centrosymmetric octahedral complex the two independent Ru–N bonds are equal within experimental error (average Ru–N 214.0 pm). The rather short Ru–S bonds (227.6 pm) indicate a very weak trans-influence of the – SO3H ligand. Caused by the protonation, one of the S–O bonds in the –SO3H ligand is long (161.4 pm), the other two are short (mean 148.0 pm). The complex units are linked by pairs of O-H ··· O hydrogen bonds (268.9 pm) to form rods parallel b (symmetry (b) · T), which in turn are held together by N–H ··· O bonds in a pseudo-hexagonal array. A packing coefficient of 0.76 is estimated.