Diverse structures and adsorption properties of quasi-Werner-type copper(ii) complexes with flexible and polar axial bonds

Abstract

The quasi-Werner-type copper(II) complex, [Cu(PF 6 ) 2 (4-mepy) 4 ] (1), in which 4-mepy is the 4-methylpyridine ligand, has flexible and polar axial bonds of Cu-PF 6 . Flexibility of the Cu-PF 6 bonds induces diverse and unprecedented guest-inclusion structures, such as. Exposure of the dense form, a-1, to benzene vapor affords the benzene-inclusion complex {[Cu(PF 6 ) 2 (4-mepy) 4 ]•2benzene} (g-1…2benzene), all benzene guests of which are easily removed by vacuum drying, reforming guest-free, dense a-1¢ with smaller sized crystals than a-1. In contrast to a-1, which shows almost no CO 2 adsorption, a-1¢ adsorbs CO 2 gas with structural transformations, this being the first example that exhibits adsorption of gas in a dense Werner-type complex and a drastic change in adsorption properties depending on the size of the crystals.

Bis[μ-3,5-bis(pyridin-2-yl)pyrazolato]bis[(hexafluorophosphato)copper(II)]

“…The distance of Cu-F1 is 2.4027 (14) Å. To the best of our knowledge, the crystal structure report of PF 6 -coordinated Cu II complex is only a few examples (Noro et al, 2011). The adjacent dinuclear complexes are stacked in columns through a weak π-π stacking interaction between pyridyl and pyrazol rings of the bpypz -ions (centroid-centroid distance 3.879 Å) and C-H···F hydrogen bonds between the bpypzand the PF 6 -ions ( Table 2).…”

Synthesis, Crystal Structure, and Adsorption Properties of Werner-type Cu(II) Complex [Cu(CF3SO3)2(4-methylpyridine)4]

“…Because ¡-PAC-1-PF 6 possesses no vacant space, the observed adsorption behavior with large hysteresis should be associated with gate-opening processes, in which adsorption occurs with structural transformations. 4 On the other hand, ¡-PAC-1-CF 3 SO 3 scarcely adsorbs CO 2 gas over the entire pressure range. In general, the gate-opening pressure depends on the strength of hosthost and/ or hostguest interactions.…”

“…4 The dense ¡-form, ¡-PAC-1-PF 6 , has inorganic PF 6 ¹ anions covered with only fluorine atoms in the framework, and it adsorbs CO 2 gas with structural transformations; this is the first example of gas-adsorption properties in the dense ¡-form. On the other hand, when ¡-PAC-1-PF 6 is recrystallized from acetone/n-hexane and 2-butanone/n-hexane, some of the weakly coordinated PF 6 ¹ anions are easily released from the axial sites and Lewis-base guests (acetone and 2-butanone) attach to these sites instead, forming the guest-including £-form, £-{[Cu(PF 6 ) 2 (4-mepy) 4 ][Cu(PF 6 )(4-mepy) 4 (PF 6 )(4-mepy) 4 (2-butanone)]¢PF 6 ¢3.5(2-butanone)} (£-PAC-1-PF 6¸2 .25(2-butanone)). The prefix "quasi-" derives from such labile axial bonds.…”

“…In this letter, we report the synthesis, crystal structure, and adsorption properties of a derivative of ¡-PAC-1-PF 6 , ¡-[Cu(CF 3 SO 3 ) 2 (4-mepy) 4 ] (¡-PAC-1-CF 3 SO 3 ), to investigate the effect of inorganic anions on the adsorption properties. The introduction of CF 3 SO 3 ¹ anions enhanced the intermolecular interactions through the oxygen atoms of the anions and inhibited gas adsorption with structural changes.…”

“…1a Among them, [Ni(NCS) 2 (4-mepy) 4 ] has been thoroughly studied because of its interesting guest-inclusion properties derived from pseudopolymorphism, such as a dense ¡-form, and guest-including ¢-and £-forms. The ¡-form has no space for including guest molecules because of its dense packing structure, whereas the ¢-and £-forms are channel-type and layer-type clathrates, respectively.…”