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Lanthanide N,N'-piperazine-bis(methylenephosphonates) (Ln=La, Ce, Nd) that display flexible frameworks, reversible hydration and cation exchange

DOI: 10.1016/j.jssc.2009.07.019 DOI Help

Authors: John Mowat (University of St Andrews) , John Groves (University of St Andrews) , Michael Wharmby (Diamond Light Source) , Stuart Miller (University of St Andrews) , Yang Li (University of St Andrews) , Philip Lightfoot (University of St Andrews) , Paul Wright (University of St Andrews)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Solid State Chemistry , VOL 182 (10) , PAGES 2769-2778

State: Published (Approved)
Published: October 2009

Abstract: Hydrothermal syntheses of lanthanide bisphosphonate metal organic frameworks comprising the light lanthanides lanthanum, cerium and neodymium and N,N?-piperazine bis(methylenephosphonic acid) (H2L(1) and its 2-methyl and 2,5-dimethyl derivatives (H2L(2) and H2L(3)) gives three new structure types. At elevated starting pH (ca. 5 and above) syntheses give ‘type I’ materials with all metals and acids of the study (MLnLxH2O, M=Na, K, Cs; Ln=La, Ce, Nd; x?4: KCeL(1)·4H2O, C2/c, a=23.5864(2) Å, b=12.1186(2) Å, c=5.6613(2) Å, ?=93.040(2)°). The framework of structure type I shows considerable flexibility as the ligand is changed, due mainly to rotation around the –N–CH2– bond of the linker in response to steric considerations. Type I materials demonstrate cation exchange and dehydration and rehydration behaviour. Upon dehydration of KCeL·4H2O, the space group changes to P21/n, a=21.8361(12) Å, b=9.3519(4) Å, c=5.5629(3) Å, ?=96.560(4)°, as a result of a change of the piperazine ring from chair to boat configuration. When syntheses are performed at lower pH, two other structure types crystallise. With the ‘non-methyl’ ligand 1, type II materials result (LnL(1)H2L(1)·4.5H2O: Ln=La, P?1, a=5.7630(13) Å, b=10.213(2) Å, c=11.649(2) Å, ?=84.242(2)°, ?=89.051(2)°, ?=82.876(2)°) in which one half of the ligands coordinate via the piperazine nitrogen atoms. With the 2-methyl ligand, structure type III crystallises (LnHL(2)·4H2O: Ln=Nd, Ce, P21/c, a=5.7540(9) Å, b=14.1259(18) Å, c=21.156(5) Å, ?=90.14(2)°) due to unfavourable steric interactions of the methyl group in structure type II.

Journal Keywords: Phosphonates; Metal–organic frameworks; Cation exchange; Lanthanides

Subject Areas: Chemistry, Materials

Instruments: I11-High Resolution Powder Diffraction

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