Coordination polymers and monomers based on new aminocarboxylate ligands: a cadmium(II) polymer containing dimeric aqua-bridged cadmium complex governed by polymeric chain

Abstract

The synthesis and characterization of novel coordination polymers [Co(HCCB)(H₂O)₂]_n (1), [Zn(HCCB)(H₂O)2]_n (2), {[Cd(HCCB)₂]·0.5[Cd(μ-H₂O)(H₂O)₄]₂}_n (3) and [Cu(HCCB)(H₂O)₂]_n (4) based on 3-(carboxymethylamino)-4-chlorobenzoic acid (H₃CCB) and mononuclear complexes [Cu(HBCCB)(H₂O)]·H₂O (5), [Co(HBCCB)(H₂O)]·H₂O (6), [Zn(HBCCB)(H₂O)] (7) and [Cd(HBCCB)(H₂O)] (8) containing 3-bis(carboxymethylamino)-4-chlorobenzoic acid (H₃BCCB) have been described. The compounds under investigation have been characterized by elemental analyses, spectral studies and structures of 1–3 and 5 determined crystallographically. Structural data of 1 and 2 revealed that the deprotonated HCCB^2- bridges metal centers leading to a double stranded 1D chain. On the other hand, the HCCB^2- coordinated thorough carboxylate oxygen and amino nitrogen in 3 to afford a 1D chain whose charge neutrality is maintained by inclusion of aqua-bridged dimer [{Cd(μ-H₂O)(H₂O)₄}₂]⁴⁺. Strong Cu⋯Cl interaction (2.754 Å) in 5 imposes a coordination geometry that is half-way between the square planar and square pyramidal. The H₃CCB, H₃BCCB and 1–3 and 5 are fluorescent at rt. Thermal studies (TG and DSC) on 1–3 suggested higher stability of 2 relative to 1 and 3 [ΔH_f (kcal/mol), ΔS = 152.17, 0.60, 1; 195.56: 0.86, 2; 69.33:0.36, 3].