Syntheses, Crystal Structures And Properties Studies Of Phosphonate Coordination Polymers

This paper summarizes the hydrothermal/solvothermal synthesis of compounds based on the flexible ligand as1-hydroxyethane-1,1-diyldiphosphonic acid (H5L1), N,N’-piperazinebis(methylenephosphonate)(H4L2) under the effect of different N-heterocyclic compound. We have obtained ten seven structural compounds (1)-(7), the crystal structures have been determined by IR, XRD, single crystal X-ray diffraction, thermal analysis (TG-DSC) and elementary analysis. Their thermal stabilities and fluorescence propertiies are studied. Here, we represent ten new compounds as:(1)[Cu(H3L1)(2,2’-bipy)];(2)[Cu2(H4L)2(H3L1)(2,2’-bipy)2];(3)[Cu(H4L1)2(2,2’-bipy)]·H2O;(4)[Cu(H3L1)(phen)]-HOCH2CH2OH;(5)[Ba2(L2)(H2O)9]-3H2O;(6)[Mg1.5(H2O)9](L2-H2)·3H2O;(7)2H3BTC-H4L2-2H2O; Ligand abbreviations: H5L1=1-hydroxyethane-1,1-diyldiphosphonic acid, HEDP,[H3CC(OH)(PO3H2)2] H4L2=N,N’-piperazinebis(methylenephosphonate), PIPO3[H2O3PCH2N(C4H8)NCH2PO3H2] H3BTC=1,3,5-benzenetricarboxylic acid, Phen=1,10-phenanthroline2,2’-bipy=2,2’-bipyridine,4,4’-bipy=4,4’-bipyridineSingle-crystal X-ray diffraction and fluorescence analysis reveals:Compound (1) involves a unique Cu(Ⅱ) atom, and H3L1-is a chelate-bridge tridentate. Compound (1)(λex=233nm) exhibits a weak peak at488nm and a strong broad peak emitted at423nm with a small shoulder peak centered at387nm. The fluorescent intensity of the maximum of (1) is stronger than that of the free2,2’-bipy ligand, largely due to the coordinated effection of the2,2’-bipy ligand with copper(II) ions.The asymmetric unit of (2) contains two distinct Cu(Ⅱ) atoms. Both Cu(1) and Cu(2) centers are in a distorted square pyramidal environment with O(6)/O(10) atom as vertices, and display five-coordinate. The phosphonate ligand H5L1in (2) displays three types of coordination modes simultaneously H5L1-complex of (1)(λex=233nm) displays a stronger fluorescent emission centered at423.5nm with a weak shoulder peak centered at382nm.The asymmetric unit of (3) contains one half distinct Cu(Ⅱ) center. Cu(1) center in (3) is in a’4+2’elongated octahedral coordination environment, Compound (3) displays one strong fluorescent peak which is located434.5nm. The fluorescent intensity of the maximum of (3) is weaker than that of the free2,2’-bipy ligand, largely due to the quenching effect of copper(Ⅱ) ions.The asymmetric unit of (4) contains a distinct Cu(Ⅱ) centre. Cu(1) center is in a distorted’4+1’square pyramid environment with O(6A) atom as vertice, the fluorescent emissions of (4)(λex=235nm) display one strong fluorescent peak at434.5nm.Compound (5) contains two crystallographically independent Ba(II), which are8-and9-coordinated, respectively. The compound (5) with Ba(II) ion displays two main fluorescent bands at378.5nm and433nm with shoulder peak at300nm. These fluorescent bands could come from the intraligand π*-n transition state of H4L2.Compound (6) possesses a zero-dimensinal mononuclear structure, in which the asymmmtric unit contains one and a half crystallogaphically independent metal cations Mg(II) with is centred adopts octahedral configuration. Compound (6) displays two strong fluorescent emission bands which are located at378nm and434.5nm, and a weak fluorescent emission band at302nm (λex=336nm). These fluorescent bands could come from the intraligand π*-n transition state of H4L2.The asymmetric unit of (7) includes a H4L2, a H3BTC and a lattice water molecule. Along the b-axis, there are two types of1-D supramolecular chain. The maximum of the emission bands is located at458nm (λex=385nm) which is in visible spectra, so the emission bands of (7) may be from the synergistic effect of between H3BTC and H4L2ligands. Both (7) and H4L ligand show two quasi-reversible one-electron redox couple. The absorption bands for (7) centered at230.0nm and269.2nm may be attributed to the π-π*and n-π*transitions of H3BTC. In order to have a better understanding on the geometries, electronic absorption spectra and charge transfer properties of this compound, a theoretical study was conducted.The TG-DSC investigations show all compound’s structure are highly stable, and the collapse temperature of skeletons are (1)280℃,(2)380℃,(3)465℃,(4)440℃,(5)400℃,(6)350℃and (7)404℃, respectively.