Heterometallic Zn₆Ti₂ Building Block Persistent in Metal-organic Frameworks Based on Asymmetrically Substituted Dicarboxylate Ligands

Experimental

Materials and Methods.

All the reagents were commer-cially available and used as received except for H3(obpdc) which was purified by recrystallization before use. IR data were recorded on KBr pellets using a Varian FTS 1000 instru-ment.

Synthesis of [H2N(CH3)2][Zn3(µ3-OH)Ti(obpdc)3(O3CH)] (1). Titanium(IV) isopropoxide (29.6 µL, 0.10 mmol) was added to a solution of H3obpdc (77.7 mg, 0.30 mmol) in DMF (3.5 mL) to form an orange colored turbid mixture. After stirring for 30 min zinc nitrate hexahydrate (51.4 mg, 0.17 mmol) and formic acid (3.8 µL, 0.1 mmol) were added to it. The final mixture was well-stirred for 2 h at room temperature and then filtered. The solution was heated in a sealed glass vial with the following steps: 1 day at 75 °C, 2 days at 95-100 °C and 1 day at 120 °C. The product was separated from the orange-colored suspension, thoroughly washed with fresh DMF and soaked in dichloromethane before drying under vacuum at room temperature for 12 h and then at 100 °C for 5 h (42.7 mg, 68％). Calcd: C, 48.4; H, 2.8; N, 1.3; Ti, 4.3％. Found: C, 48.7; H, 2.9; N, 1.2; Ti, 4.1％.

X-ray Powder Diffraction. X-ray powder diffraction patterns were recorded at the 2D SMC beamline of the Pohang Accelerator Laboratory, Korea. Crystalline samples were thoroughly ground in an agate mortar and packed in a capillary tube (0.3 mm diameter). Debye-Scherrer diffraction data were collected on an ADSC Quantum-210 detector with a fixed wavelength (λ = 1.40000 Å) and an exposure of 60 sec. The ADX program7 was used for data collection, and Fit2D program8 was used to convert the 2D to 1D patterns.

X-ray Single-crystal Diffraction. Single-crystals of as-synthesized 1 were directly picked up from the mother liquor with a cryoloop attached to a goniohead, and trans-ferred to a cold stream of liquid nitrogen (−173 °C). The data collection was carried out using synchrotron X-ray on a ADSC Quantum 210 CCD detector with a silicon (111) double-crystal monochromator at 2D SMC beamline of the Pohang Accelerator Laboratory, Korea. The ADSC Quantum- 210 ADX program7 was used for data collection, and HKL3000sm (Ver. 703r)9 was used for cell refinement, data integration, and absorption correction. After space group determination, the structures were solved by direct methods and subsequent difference Fourier techniques (SHEXLTL).10 All the non-hydrogen atoms were refined anisotropically, and hydrogen atoms were added to their geometrically ideal positions. The diffused electron densities in the void space could not be modeled properly, and were removed from the reflection data using the SQUEEZE routine of PLATON.11 The results of SQUEEZE process were attached to the CIF file. The crystal data and results of structure refinements are summarized in Table S1. Crystallographic data for the structure reported here have been deposited with CCDC (Deposition No. CCDC-981813 (1)). These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, E-mail: deposit@ccdc.cam.ac.uk

Gas Sorption. Gas sorption isotherms were measured in a bath of liquid nitrogen (77 K) with a Belsorp Mini-II. The gases used were of the highest quality available (N60 for H2, N50 for Ar and N2, and N45 for O2). Typically, 100-150 mg of solvent-exchanged samples were evacuated under a dynamic vacuum at room temperature for 12 h. The equilibrium criteria were set consistent throughout all the measurements (change in adsorption amounts less than 0.1 cm3/g within 180 sec). Complete gas sorption isotherms are shown in Fig. S2.