Host−Guest Chemistry of 1D Suprachannels and Dihalomethane Molecules: Metallacyclodimeric Ensembles Consisting of Zinc(II)-2,7- bis(nicotinoyloxy)naphthalene Complexes Minwoo Park, Hyeun Kim, Haeri Lee, Tae Hwan Noh, and Ok-Sang Jung* Department of Chemistry, Pusan National University, Pusan 609-735, Korea * S Supporting Information ABSTRACT: Self-assembly of ZnX 2 (X = Cl, Br, and I) with 2,7-bis(nicotinoyloxy)- naphthalene (L) as a hemicircular bidentate ligand containing a chromophore moiety yields a systematic metallacyclodimeric unit, [ZnX 2 (L)] 2 . These basic skeletons constitute, via interdigitated π···π interactions, a unique columnar ensemble forming a suprachannel. This can then be employed as an unusual “diiodomethane within the suprachannel” host−guest system, CH 2 I 2 @[ZnX 2 (L)] 2 . Specifically, the suprachannel significantly stabilizes the CH 2 I 2 molecules in the order [ZnI 2 (L)] 2 > [ZnBr 2 (L)] 2 > [ZnCl 2 (L)] 2 . This suprachannel has significant halogen effects on the photoluminescence (PL), thermal properties, and host−guest inclusion. ■ INTRODUCTION Arrays of molecular units, especially after the emergence of additional functionalities, have beckoned crystal engineers for the past decade. 1−11 Indeed, the field of supramolecular materials, manipulation of molecular ensembles is both an attractive topic and, not coincidentally, an enticing chal- lenge. 8−11 A rigorous knowledge and understanding of the driving forces behind those ensembles is prerequisite to the design and construction of molecular arrays. Syntheses of metallacyclic molecules and their arrays are particularly coveted goals, 12−19 in the fields of molecular adsorption, recognition, ion exchange, confinement catalysis, and luminescent chemo- sensing, since their functions are comparable with organic crown-ether, cyclodextrins, calixarenes, and cucurbiturils. 20−26 Some hemicircular bidentate N-donors provide, via the introduction of appropriate metal ions, wider opportunities for task-specific metallacycles as receptors. 12,13 Thus, on the basis of the geometry of the metal ions, the binding sites of the donating ligands, the reactivity, the length, and the charge of the spacers, various metallacycles for host−guest recognition systems have been designed and synthesized. Specifically, zinc(II) complexes of functional N-donor ligands have been extensively examined for metallo-enzymes, zinc finger proteins, transmetalation, recognition, photoluminescence (PL), and catalysts. 27−33 As regards systematic research on the construction and recognition of “specific guests within a zinc(II) metallacyclic suprachannel containing chromophore moiety”, simple recog- nition systems have been reported, though the field remains relatively unexplored. In this context, two crucial aims of the present study were to explore the behavior of the included unstable haloalkanes within the open cavity of columnar suprachannels consisting of zinc(II) metallacyclodimers and to investigate the metallacyclodimeric system’s significant halogen effects. Herein, we report the construction of task-specific zinc(II) metallacyclodimers as functional halomethane contain- ers and evaluate their PL and thermal properties. The metallacyclic system consisting of the three ZnX 2 (X − = Cl − , Br − , and I − ) was designed as selective receptors for dichloro- methane, dibromomethane, and diiodomethane, respectively. 12 This suprachannel system is the effective stabilizer for diiodomethane, which is known to decompose upon exposure to light and release iodine. 34 With its high density, diiodo- methane is useful as a reagent for the determination of mineral- and other solid-sample densities, as an optical contact liquid, and as carbene. 35 ■ EXPERIMENTAL SECTION Materials and Measurements. All chemicals, including zinc(II) chloride, zinc(II) bromide, zinc(II) iodide, 2,7-dihydroxynaphthalene, nicotinoyl chloride hydrochloride, and triethylamine, were purchased from Aldrich and used without further purification. Elemental microanalyses (C, H, N) were performed on crystalline samples at the KBSI Pusan Center using a Vario-EL III. Thermal analyses were undertaken under a nitrogen atmosphere at a scan rate of 10 °C/min using a Labsys TGA-DSC 1600. The infrared spectra of samples prepared as KBr pellets were obtained on a Nicolet 380 FT-IR spectrophotometer. 1 H (300 MHz) and 13 C (75 MHz) NMR spectra were recorded on a Varian Mercury Plus 300 with calibration against the solvent signal (CDCl 3 : δ = 7.26 ppm for 1 H NMR; δ = 77.16 ppm for 13 C NMR). Scanning electron microscopy (SEM) images were obtained on a Tescan VEGA 3. Powder X-ray diffraction data were recorded on a Rigaku RINT/DMAX-2500 diffractometer at 40 kV and 126 mA for Cu Kα. Excitation and emission spectra were acquired on a FluoroMate FS-2 spectrofluorometer. 2,7-Bis(nicotinoyloxy)naphthalene (L). Triethylamine (22 mmol, 2.67 g) was added to a stirred mixture of 2,7-dihydroxynaph- thalene (5 mmol, 0.80 g) and nicotinoyl chloride hydrochloride (12 mmol, 2.14 g) in chloroform (120 mL) at 60 °C. The reaction mixture Received: April 21, 2014 Published: August 7, 2014 Article pubs.acs.org/crystal © 2014 American Chemical Society 4461 dx.doi.org/10.1021/cg5009889 | Cryst. Growth Des. 2014, 14, 4461−4467