Transformation of a C-methylcalix[4]resorcinarene-based host–guest complex from a wave-like to a novel triangular brick-wall architecture

Bao-Qing Ma, Philip Coppens
2003 Chemical Communications  
A novel 2D triangular brick-wall framework based on CMCR and bpe with included ruthenocene guest molecules is formed with time by conversion of a 1D wave-like polymer structure with an accompanying bowl-to-boat conformational change of the CMCR molecules. Solid state host-guest assembly has attracted intensive interests because of its applications in fields as diverse as nonlinear optics, sensors and micro-reaction vessels. 1,2 Guests in host materials like cyclodextrins, clathrates and
more » ... may exhibit photophysical properties significantly different from those of neat crystals. It has recently been demonstrated that Cmethylcalix[4]resorcinarene (CMCR) forms supramolecular frameworks with bifunctional pillars such as 4,4A-bipyridine, capable of including molecular guests of interest. The various frameworks show great diversity and include capsule, brickwall, wave-like and stepped networks, 3,4 which allow guests of different size and shape to be entrapped. The major impetus for the inclusion of ruthenocene and decamethylruthenocene within the host framework are their long luminescence lifetimes, 5 as well as the significant geometry change upon excitation established by spectroscopic experiments and theoretical calculations. 6-9 Because of the molecular dilution achieved such complexes are potential candidates for time-resolved photocrystallography. 10 Surprisingly, though many examples of ferrocene inclusion compounds, such as (DCA) 2 ·Fe(C 5 H 5 ) 2 (DCA = deoxycholic acid), 11 2(a-CD)·Fe(C 5 H 5 ) 2 , 12 CMCR·mbipy·nFe(C 5 H 5 ) 2 13,14 (m = 2, n = 1; m = 1.5, n = 0.85) and Pd 6 (tpt) 6 (2,2Abipy) 6 ·[Fe(C 5 H 5 ) 2 ] 4 15 (tpt = 1,3,5-tri(4-pyridyl)-2,4,6-triazine) have been described, the only report on inclusion of ruthenocene or its derivatives in a supramolecular framework is that on the CMCR·2bipy·decamethylruthenocene complex. 16 We report here the first example of a transformation from a wave-like to a not previously observed triangular brick-wall structure, which is accompanied by a conformational change of CMCR from a bowl to a boat-like (flattened cone) structure, leading to a supramolecular isomer of identical framework composition, but different structural connectivity. trans-1,4-Bis(pyridyl)ethylene (bpe), a longer spacer than bipy, is used to assembly a host-guest complex in the presence of ruthenocene. Two novel complexes of composition CMCR·2bpe·ruthenocene·ethanol 1 and CMCR·2bpe·ruthenocene 2 have been prepared as follows. A clear solution obtained by heating a mixture of CMCR (0.05 mmol, 27.2 mg), trans-1,4-bis(pyridyl)ethylene (0.1 mmol, 18.2 mg) and ruthenocene (0.1 mmol, 23.1 mg) in 3 ml ethanol solution was kept at room temperature. Yellow blockshaped crystals of 1 were obtained within 1 day. They converted to yellow prismatic crystals of 2 after being kept in solution for one week, † indicating compounds 1 and 2 to be kineticallycontrolled and thermodynamically-stable phases, respectively. X-Ray diffraction analysis revealed that the framework of 1 consists of a wave-like polymer as depicted in Fig. 1 . ‡ CMCR adopts a bowl-like conformation with four intramolecular hydrogen bonds [O3...O2 = 2.938(6) Å, O3-H3...O2 = 171(5)°; O4...O1 a = 2.774(6) Å, O4-H4...O1 a = 165(6)°; a 2x, y, 2z + 3/2] along the upper rim of CMCR. Four O-H...N
doi:10.1039/b212548j pmid:12638971 fatcat:zhx2inkoxjgihlg7u6gt64tvb4