Fig. 1.

MOF-2000 is a periodic framework harboring controlled component heterogeneity. (A) Chemical structures of organic struts H₂L_r and H₂L_b⁴⁺ incorporated in MOF-2000 (Methods Summary), and the MOF-2000 crystal structure [key: carbon, black; oxygen, red; Zn₄O(CO₂)₆ polyhedra, blue; all hydrogen atoms have been omitted for clarity]. (B) Optical images of MOF-2000 single crystal: without polarizer (up) and in between crossed polarizers (down). The lack of birefringence indicates that MOF-2000 is optically isotropic. The edge of the crystal is about 0.1 mm. (C) As determined by ¹H-NMR and powder X-ray diffraction measurements (SI Appendix, sections S1.3 and S1.4), MOF-2000 consists of a twofold interpenetrated crystalline framework (of topology pcu-c) of 2:1 L_r:L_b ratio (estimated 5% error), for a wide range of solution ratios (shaded region). (D) MOF-2000 therefore combines the regularity of a covalent framework with controlled irregularity of its components.