Framework Engineering by Anions and Porous Functionalities of Cu(II)/4,4‘-bpy Coordination Polymers

A combination of framework-builder (Cu(II) ion and 4,4‘-bipyridine (4,4‘-bpy) ligand) and
framework-regulator (AF6 type anions; A = Si, Ge, and P) provides a series of novel porous coordination
polymers. The highly porous coordination polymers {[Cu(AF6)(4,4‘-bpy)2]·8H2O}n (A = Si (1a·8H2O), Ge
(2a·8H2O)) afford robust 3-dimensional (3-D), microporous networks (3-D Regular Grid) by using AF62-
anions. The channel size of these complexes is ca. 8 × 8 Å2 along the c-axis and 6 × 2 Å2 along the a-
or b-axes. When compounds 1a·8H2O or 2a·8H2O were immersed in water, a conversion of 3-D networks
(1a·8H2O or 2a·8H2O) to interpenetrated networks {[Cu(4,4‘-bpy)2(H2O)2]·AF6}n (A = Si (1b) and Ge (2b))
(2-D Interpenetration) took place. This 2-D interpenetrated network 1b shows unique dynamic anion-exchange properties, which accompany drastic structural conversions. When a PF6- monoanion instead
of AF62- dianions was used as the framework-regulator with another co-counteranion (coexistent anions),
porous coordination polymers with various types of frameworks, {[Cu2(4,4‘-bpy)5(H2O)4]·anions·2H2O·4EtOH}n (anions = 4PF6- (3·2H2O·4EtOH), 2PF6- + 2ClO4- (4·2H2O·4EtOH)) (2-D Double-Layer), {[Cu2(PF6)(NO3)(4,4‘-bpy)4]·2PF6·2H2O}n (5·2PF6·2H2O) (3-D Undulated Grid), {[Cu(PF6)(4,4‘-bpy)2(MeCN)]·PF6·2MeCN}n (6·2MeCN) (2-D Grid), and {[Cu(4,4‘-bpy)2(H2O)2]·PF6·BF4}n (7) (2-D Grid), were obtained,
where the three modes of PF6- anions are observed. 5·2PF6·2H2O has rare PF6- bridges. The PF6- and
NO3- monoanions alternately link to the Cu(II) centers in the undulated 2-D sheets of [Cu(4,4‘-bpy)2]n to
form a 3-D porous network. The free PF6- anions are included in the channels. 6·2MeCN affords both free
and terminal-bridged PF6- anions. 3·2H2O·4EtOH, 4·2H2O·4EtOH, and 7 bear free PF6- anions. All of the
anions in 3·2H2O·4EtOH and 4·2H2O·4EtOH are freely located in the channels constructed from a host
network. Interestingly, these Cu(II) frameworks are rationally controlled by counteranions and selectively
converted to other frameworks.