alpha- and beta-bis(1,1,1-trifluoro-5,5-dimethyl-5-methoxyacetylacetonato)copper(II): Transforming the dense polymorph into a versatile new microporous framework

Bis(1,1,1-trifluoro-5,5-dimethyl-5-methoxy-acetylacetotato)copper(II) was p repared in two polymorphic modifications. The orthorhombic alpha-form is st able and densely packed, with four trans and four cis square bischelate bui lding blocks per unit cell. These are connected through additional coordina tion bonds to form a dense polymer network. For the trigonal beta-form, the square bischelate complex units are present exclusively as the trans isome rs. The distinctive assembly of these units results in a lattice with an op en pore volume of about 17% that is accessible to a wide range of guests. T he compound has a remarkably strong affinity for the porous beta-form as ev ident from the efficient alpha-to-beta conversion on contact not only with liquid guests but also with organic vapors at pressures well below the satu ration pressure. Although the open beta-form is metastable, it has a remark able kinetic stability, most likely because of the trans-to-cis isomerizati on that must accompany the beta-to-alpha transformation. Many sorbents play a dual role as stabilizing guest and as catalyst promoting the alpha-to-be ta or beta-to-alpha conversion. Because of its versatile sorption propertie s and relative robustness. the beta-form of the complex can be classified a s a novel organic zeolite mimic.