Triple-armed aliphatic tricarboxylic acids as sources of ligands for uranyl ion: influence of bridgehead functionalization?

CrystEngComm Pub Date: 2023-06-13 DOI: 10.1039/D3CE00526G

Abstract

The two triple-armed species tris(2-carboxyethyl)nitromethane (H3tcenm) and tris(2-carboxyethyl)phosphine (H3tcep) have been used to synthesize seven uranyl ion complexes under (solvo)-hydrothermal conditions and in the presence of various structure-directing cations. The three carboxylate groups chelate three different cations and the nitro group is uncoordinated in [H2NMe2][UO2(tcenm)]·3H2O (1), [C(NH2)3][UO2(tcenm)]·0.5H2O (2) and [PPh3Me][UO2(tcenm)] (3), which crystallize as diperiodic coordination polymers with the hcb topology and minor variations in shape depending on the counterion. The two isomorphous complexes [UO2(tcenm)M(bipy)2][UO2(tcenm)]·3H2O, with M = Ni (4) or Cu (5) and bipy = 2,2′-bipyridine, display the same arrangement, with a M(bipy)22+ group bridging two adjoining carboxylate donors in one uranyl equatorial plane. [(UO2)2(tcenm)2Cu(R,S-Me6cyclam)]·2H2O (6), where R,S-Me6cyclam = 7(R),14(S)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, is the only triperiodic framework in the series, with the tcs topology resulting from CuII pillaring diperiodic, uranyl-based sql networks. H3tcep is oxidized in situ to give the phosphine oxide H3tcepo, which is partially deprotonated in [UO2(Htcepo)] (7); the phosphine oxide and the two carboxylate groups are coordinated, and the diperiodic, three-dimensional network formed has the point symbol {66} and the vertex symbol 62·62·63·66·64·64, with the rings involved in Hopf links formation. Only complexes 3 and 7 are significantly emissive in the solid state, with photoluminescence quantum yields of 9%, and the emission maxima positions are in agreement with the number of uranyl equatorial donors.

Graphical abstract: Triple-armed aliphatic tricarboxylic acids as sources of ligands for uranyl ion: influence of bridgehead functionalization
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