The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with tert-butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor 7c with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue 7c-d(4) by solid state (2)H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-d(4) rotator in the kHz regime.

In this work, we describe the synthesis and solid-state characterization of a series of molecular rotors with tri-isopropylsilyloxy-substituted (TIPS) trityl stators axially linked to 1,4-diethynylphenylene, 3,6-diethynyl-1,2-difluorophenylene and 2,5-diethynylpyridine rotators to produce 1,4-bis [(3,3- (3). The subsequent removal of the TIPS protecting group led to their corresponding hydroxyl-substituted trityl derivatives (4) and (5). TIPS-and HO-substituted stators are involved in different inter-and intramolecular interactions (hydrogen bonding, phenyl embraces, C-H-p interactions) that give rise to isomorphic packing motifs that constrained the rotational dynamics in the solid-state to the slow exchange regime. Crystallographic Data Centre as supplementary publication nos. CCDC 943819 (4a-acetone), 943820 (4b-methanol), 943821 (4c-DMSO), 943496 (2) and 943497 (1), these data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.uk/data_request/cif. See Fig. 7 Crystal packing of solvates 4 in (a) acetone 4a, (b) DMSO 4c and (c) methanol 4b, view along b axis. Scheme 2 Synthesis of molecular rotors 4 and 5.This journal is

The synthesis and crystal structure of three new molecular rotors derived from levonorgestrel and norethisterone are reported. The conformation, close contacts, and shape characteristics of these molecules exhibiting Z′ = 2 and the inclusion of solvent molecules were analyzed together with the crystal structures of parent molecules retrieved from the Cambridge Structural Database. For the set of estranes studied, we confirmed that whenever an alternative conformer cannot satisfy the crystallographic symmetry, a second molecule is incorporated in the asymmetric unit resulting in conformational isomorphism (Z′ > 1). The shape of these molecules could make them interesting as potential hosts.

Thirteen steroidal derivatives were synthesized through a Sonogashira cross-coupling reaction which has been found to be an excellent synthetic strategy to introduce halo-aromatic groups into C-17-ethynyl substituted steroidal frameworks. The structural modification was performed on ethynylestradiol, mestranol, norethisterone, ethisterone and 3-ethynyl-3-epi-sarsasapogenin. The solid state study by X-ray diffraction showed that most of them belong to the orthorhombic P2 1 2 1 2 1 space group and the whole family has an "L" conformation, regardless of the nature of the steroid A-ring (3-hydroxy-aromatic or 3-oxo). Due to the presence of several moieties which are susceptible to forming secondary interactions, the crystalline packing is governed by O-H⋯O, C-H⋯O, and C-H⋯π interactions, and only 17α-(4′-iodophenylethynyl)-3-methoxy-estra-1,3,5(10)-trien-17-β-ol (mestranol derivative 3) showed an iodine-iodine interaction (d I⋯I = 4.116 Å). The crystalline packing for ethynylestradiol derivatives 1, 2 and 4 showed the formation of holes with diameters greater than 5.2 Å suggesting their potential application in host guest chemistry or as porous materials.

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