The infinite 1D chain structure is the simplest topology of coordination polymers
(CPs); however, the complicated crystal packing modes of the 1D chains make their solidstate
structures diversified, thereof endow different potential applications.1 It is reported that
2-thiophenecarboxylic acid possesses biological properties being used in hypercalcemic
treatment2, while Schiff bases are known to be used to design medicinal compounds.
Herein we report crystal structures of two 1D CPs, {[Cd2(4-bpmhz)2(2-tpca)4]
(4-
bpmhz)}n (1) and [Cd2(3-bpmhz)2(2-tpca)4]n (2) constructed from the semi-rigid Schiff-base
N,N'-type ligands, 1,2-bis(pyridin-4-ylethylidene)hydrazine (4-bpmhz), or 1,2-bis(pyridin-3-
ylethylidene)hydrazine (3-bpmhz) and 2-thiophenecarboxylic acid (2-tpca). The structures of
compounds were determined using X-ray diffraction method (Figure).

Figure. a) the fragment of polymeric chain in 1; b) packing of the chains in 1 with
accommodation of free 4-bpmhz.

Compound 1 crystallizes in the monoclinic I2/a space group: a=14.4222(4),
b=16.8312(5), c=26.2099(10) Å, =102.903(3) °, V=6201.7 Å3. For 2, triclinic P-1 space
group: a=14.6315(9), b=14.6423(8), c=14.6915(6) Å, =108.053(4), =93.091(4),
=94.753(5) °, V=2971.7(3) Å3. The metal coordination nodes in 1 and 2 represent the similar
binuclear clusters formed via chelate-bridging function of one of the 2-tpca residues. Each
Cd(II) center adopts N2O5 pentagonal bipyramidal coordination geometry with two nitrogen
donors from bipyridyl ligands, two oxygen atoms from chelating 2-tpca anion, and three
oxygen atoms from chelate-bridging 2-tpca anion. The nodes are mediated by bidentate
bridging 4-bpmhz in 1 and 3-bpmhz in 2. Both compounds exhibit one-dimensional linear
double chain structures.
1 W.L. Leong, J.J. Vittal; Chem. Rev. 111, 688–764 (2011)
2 W. Lloyd, V.S. Fang, H. Wells, A.H. Tashjian; J. Endocrinol. 85, 763–768 (1969)