“Venetian Blinds” Mechanism of Solvation/Desolvation in Palladium(II) Wheel-and-Axle Organic−Inorganic Diols

Abstract

A family of organic-inorganic wheel-and-axle diols (Pd(LOH)(2)Cl(2), Pd(LOH)(2)(CH(3))Cl, Pd(LOH)(2)(CH(3)COO)(2), LOH = alpha-(4-pyridyl)benzhydrol) and several corresponding solvates are synthesized and characterized by single-crystal X-ray diffraction analysis. Their structures are compared to investigate the factors governing the modes of solid state association, the propensity to clathration, and the structural basis of guest inclusion. In all the complexes, the palladium coordination is a slightly distorted square. The LOH ligands coordinate Pd(2+) by means of the 4-pyridyl ring. In the chloride complexes solvation occurs with a 1:2 host/guest ratio by hydrogen bonding between the terminal -OH groups of the complex diol and one acceptor atom on the guest, and it is further assisted by guest stacking between host aryl rings. All solvates are organized in layers with practically invariant metrics, while the layers may be assembled in different arrangements. The structures of the nonsolvate compounds are related to the metrics of the solvate forms by rotation of the complex molecules within the layer plane. In all cases the nonsolvates are completely converted into the corresponding crystalline solvate forms by exposure to the vapor of the guest, and conversely they are quantitatively recovered from the solvate upon removal of the guest by mild conditions. On the basis of the structural data, it is proposed that the solvation/desolvation process proceeds by a concerted rotation of the complex molecules in the layer plane. The structural analysis of Pd(LOH)(2)(CH(3)COO)(2) and of its tetrahydrofuran monosolvate form suggests that the first step of the solid/gas solvation process may imply the clathration of 1 mol of guest between the aryl rings, which successively triggers the collective reorientation of the host molecules.

Concomitant polymorphism and twinning of dichloro-bis(η5-tert-butylcyclopentadienyl)titanium(IV)

“…The molecular symmetry evaluations and exact refinement procedures are also discussed. We are interested in the design of hybrid organic-inorganic wheeland-axle systems (waad) with flexible dynamic frameworks that can create pores "on demand " to accomodate small guest molecules [1][2][3]. A reversible dynamic reorganization between the waad nonsolvate and solvate phases requires two conditions: (i) a low cost structural rearrangement between two states represented by the initial close (self-mediated)and the final open (guest-mediated) host frameworks, (ii) an easily accessible migration path for the outcoming and incoming guest molecules.…”

Fabricating organometallic wheel-and-axle compounds for the creation of dynamically porous crystalline materials

“…These are molecules or molecular assemblies formed by a linear central axle connecting two relatively bulky end groups, as depicted in Figure 2. For this reason we chose metals favouring linear or square planar coordination geometries, such as Ag(I), 13 Pd(II) or Pt(II), 14 respectively. This aspect has been reviewed by Soldatov in 2006.…”

One‐Pot Mechanosynthesis with Three Levels of Molecular Self‐Assembly: Coordination Bonds, Hydrogen Bonds and Host–Guest Inclusion

“…The target [Co-(dbm) 2 R 2 ] compounds belong to a family of metal-organic hosts, [17] known as soft supramolecular materials (SSMs), [18] based on "wheel-and-axle"-shaped building blocks. [19][20][21] The shape of SSM building blocks inhibits the formation of a close-packed solid-state structure, enabling the reversible inclusion of molecular guests. The resulting responsive guest inclusion makes SSMs popular as "soft" and "on demand" materials for molecular inclusion, alternative to rigid microporous solids, such as metal-organic frameworks.…”