Luminescent cadmium coordination polymers synthesized from bis(4-pyridylmethyl)piperazine and isophthalic acid derivatives

Abstract

Hydrothermal reaction of cadmium nitrate, 5-substituted isophthalic acid derivatives, and the long-spanning bis(4-pyridylmethyl)piperazine (4-bpmp) ligand afforded a series of crystalline coordination polymers whose topologies and mode of interpenetration depend critically on the nature of the 5-position substituent. {[Cd(mip)(4-bpmp)(H2O)]·3H2O}n (1, mip=5-methylisophthalate) and {[Cd(nip)(4-bpmp)(H2O)]·3H2O}n (2, nip=5-nitroisophthalate) both display (4,4) grid topologies. {[Cd4(hip)4(H2O)4(4-bpmpH)2](hip)·15H2O}n (3, hip=5-hydroxyisophthalate) also manifests a (4,4) grid topology, but is based on {Cd2O2} and {Cd2(OCO)2} dimeric units. [Cd(meoip)(4-bpmp)]n (4, meoip=5-methoxyisophthalate) shows a (4,4) grid topology based only on {Cd2(OCO)2} dimeric units. {[Cd9(meoip)10(4-bpmpH)2(H2O)]·2H2O}n (5) displays a complex 3D coordination polymer net comprised of trimer-based [Cd6(meoip)6]n layers linked by meoip ligands to trimer-based [Cd3(meoip)3(H2O)(4-bpmpH)2]n layers. {[Cd2(aip)2(4-bpmpH)(H2O)2](NO3)·5H2O}n (6, aip=5-aminoisophthalate) shows 3,4-connected slab motifs with (63)(66) topology. {[Cd2(tbuip)2(4-bpmp)3]·8H2O}n (7, tbuip=5-tert-butylisophthalate) exhibits 5-connected slabs with 4862 topology, that engage in parallel 2D+2D→3D interpenetration. {[Cd3(btc)2(H2O)8(4-bpmp)]·6H2O}n (8, btc=1,3,5-benzenetricarboxylate) displays 1D [Cd3(btc)2(H2O)8]n ribbons pillared by 4-bpmp ligands into 2D (6,3) hexagonal nets. {[Cd2Cl4(4-bpmp)3(H2O)2]·4-bpmp·H2O}n (9), prepared from cadmium chloride, 4-bpmp, and 1,3,5-benzenetricarboxylic acid. This shows 1D neutral {[Cd2Cl4(4-bpmp)3(H2O)2]n ladder motifs that interlock and interpenetrate in a 1D+1D→3D manner. Luminescent behavior in the cadmium complexes is ascribed to intra-ligand molecular orbital transitions. The new phases were also surveyed for the ability to detect nitrobenzene in ethanol suspension.