Transformation from a 2D stacked layer to 3D interpenetrated framework by changing the spacer functionality: Synthesis, structure, adsorption, and magnetic properties

Two novel coordination polymers of Cu(II), viz. [Cu(bipy)(1,4-napdc)(H2O)(2)](n) (1) and {[Cu(bpe)(1.5)(1,4-napdc)](H2O)}(n) (2) (bipy = 4,4'-bipyridine; bpe = 1,2-bis(4-pyridyl)ethane; 1,4-napdc(2)- = 1,4-naphthalenedicarboxylate), have been synthesized and structurally characterized by changing only the pillar motifs. Both the compounds crystallize by slow evaporation from the ammoniacal solution of the as-synthesized solid. Framework 1 crystallizes in monoclinic crystal system, space group P2/n (No. 13), with a = 11.028(19) angstrom, b = 11.16(3) angstrom, c = 7.678(13) angstrom, beta = 103.30(5)degrees, and Z = 2. Framework 2 crystallizes in triclinic system, space group, P (1) over bar (No. 2), a = 10.613(4) angstrom, b = 10.828(10) angstrom, c = 13.333(9) angstrom, alpha = 85.25(9)degrees, beta = 82.59(6)degrees, gamma = 60.37(5)degrees, and Z = 2. The structure determination reveals that 1 has a 2D network based on rectangular grids, where each Cu(II) is in 4 + 2 coordination mode. The 2D networks stacked in a staggered manner through the pi-pi interaction to form a 3D supramolecular network. In the case of 2, a {Cu(bpe)(1.5)}(n) ladder connected by 1,4-napdc(2)- results a 2D cuboidal bilayer network and each bilayer network is interlocked by two adjacent identical network (upper and lower) forming 3-fold interpenetrated 3D framework with small channel along the c-axis, which accommodates two water molecules. The TGA and XRPD measurements reveal that both the frameworks are stable after dehydration. Adsorption measurements (N-2, CO2, and different solvents, like H2O, MeOH, etc.) were carried out for both frameworks. Framework 1 shows type-II sorption profile with N-2 in contrast to H2O and MeOH, which are chemisorbed in the framework. In case of 2, only H2O molecules can diffuse into the micropore, whereas N-2, CO2, and MeOH cannot be adsorbed, as corroborated by the smaller channel aperture. The low-temperature (300-2 K) magnetic measurement of 1 and 2 reveals that both are weakly antiferromagnetically coupled (J = -1.85 cm(-1), g = 2.02; J -0.153 cm(-1), g = 2.07), which is correlated by the magnetic pathway to the corresponding structure.