Self-Assembly of Lanthanide Helicate Coordination Polymers into 3D Metal-Organic Framework Structures

Pyridine-2,6-dicarboxylic acid (pdcH2 ) reacts with nitrate salts of La(III), Ce(III), and Nd(III) under hydrothermal
conditions to form three-dimensional network structures, 1−4. All the compounds crystallize in the monoclinic space
group P21/c with the following lattice parameters:  {La2(pdc)3·3H2O} 1, a = 10.966(3) Å, b = 17.534(4) Å, c =
13.578(2) Å, β = 100.23(3)°, V= 2569.3(9) Å3, Z = 4, R1 = 0.052, wR2 = 0.143, S = 1.06; {Ce2(pdc)3·3H2O}
2, a = 12.701(3) Å, b = 9.979(1) Å, c = 19.401(4) Å, β = 97.73(2)°, V= 2436.6(8) Å3, Z = 4, R1 = 0.039, wR2
= 0.117, S = 1.30; {Ce2(pdc)3·3H2O} 3, a = 10.961(5) Å, b = 17.523(5) Å, c = 13.505(2) Å, β = 100.89(3)°,
V= 2547.2(8) Å3, Z = 4, R1 = 0.040, wR2 = 0.103, S = 1.08; {Nd2(pdc)3·3H2O} 4, a = 10.944(3) Å, b =
17.448(5) Å, c = 13.397(2) Å, β = 101.19(3)°, V= 2569.3(9) Å3, Z = 4, R1 = 0.052, wR2 = 0.143, S = 1.06.
Compounds 1, 3, and 4 form infinite single helical chains with large widths and pitches containing four metal ions
per turn while 2 forms a different helix with smaller width and pitch containing two metal ions per turn. Each helix
is further bonded on either side via carboxylate bridging producing three-dimensional metal-organic framework
structures.