Contrasting Networks and Entanglements in Uranyl Ion Complexes with Adipic and trans,trans-Muconic Acids

Abstract

adpH2) and trans,trans-muconic (trans,trans-hexa-2,4-diene-1,6dicarboxylic, mucH2) acids have been reacted with uranyl cations under solvo-hydrothermal conditions, yielding nine homo-or heterometallic complexes displaying in their crystal structure the effects of the different flexibility of the ligands. The complexes [PPh4]2[(UO2)2(adp)3] (1) and [Ni(bipy)3][(UO2)2(muc)3]5H2O (2), where bipy is 2,2ʹ-bipyridine, crystallize as diperiodic networks with hcb topology, the layers being strongly puckered or quasiplanar, respectively. Whereas [(UO2)2(adp)3Ni(cyclam)]2H2O (3), where cyclam is 1,4,8,11tetraazacyclotetradecane, crystallizes as a diperiodic network, [(UO2)2(muc)3Ni(cyclam)]2H2O (4), is a triperiodic framework in which the Ni II cations are introduced as pillars within a uranyl-muc 2framework with mog topology.[UO2(adp)(HCOO)2Cu(R,S-Me6cyclam)]2H2O (5), where R,S-Me6cyclam is 7(R),14(S)-5,5,7,12,12,14hexamethylcyclam, is a diperiodic assembly with sql topology, and it crystallizes together with [H2NMe2]2[(UO2)2(adp)3] (6), a highly corrugated hcb network with a square-wave profile, which displays threefold parallel interpenetration. In contrast, [(UO2)3(muc)2(O)2Cu(R,S-Me6cyclam)] ( 7) is a diperiodic assembly containing hexanuclear, 3-oxido-bridged secondary building units which are the nodes of a network with hxl topology. The two related complexes [PPh3Me]2[(UO2)2(adp)3]4H2O (8) and [PPh3Me]2[(UO2)2(muc)3]H2O (9) crystallize as hcb networks, but their different shapes, undulated or quasi-planar, respectively, result in different entanglements, twofold parallel interpenetration in 8 and twofold inclined 2D  3D polycatenation in 9.

Plumbing the uncertainties of solvothermal synthesis involving uranyl ion carboxylate complexes

“…Complex 2 contrasts also with that obtained from reaction in aqueous DMF with PPh 3 Me + in place of PPh 4 + , which yields [PPh 3 Me] 2 [(UO 2 ) 2 (muc) 3 ]•H 2 O, a species displaying twofold inclined polycatenation of networks with hcb topology. 52 The obvious reasons for this difference are that it arises both from the increase in pH that must result from the hydrolysis of DMF to dimethylammonium formate, and from the strong coordinating power of NMP, which is most often coordinated to the uranyl ion when used as a cosolvent, 62 and, in the present case (but not as a general rule), limits the periodicity of the polymer. The uranyl cation in 2 is κ 2 O,O′chelated by one carboxylate group and bound to three more oxygen donors from two muc 2− ligands and one NMP molecule, the uranium atom environment being thus pentagonalbipyramidal [U-O(oxo), 1.7729(15) and 1.7745(15) Å; U-O(carboxylato), 2.4266 (15) and 2.4820(15) Å for the chelating group, 2.3412(14) and 2.4217(14) Å for the others; U-O(NMP), 2.3029(15) Å].…”

“…This is at variance with the ready incorporation of phosphonium cations in the structures of uranyl ion complexes with long-chain dicarboxylates previously reported, most of which having been synthesized with DMF or no organic cosolvent (Table 3). 52,61 It is particularly notable that the complex [PPh 4 ] 2 [(UO 2 ) 2 (C6) 3 ] was obtained with NMP as cosolvent but, notwithstanding the closeness of C6 2− and muc 2− ligands, NMP does not coordinate in this case. 52 Complex 2 does not have the U/dicarboxylic acid stoichiometry of the reaction mixture designed to give rise to an anionic coordination polymer and its actual 1 : 1 U/dicarboxylate stoichiometry is that of a neutral species requiring no counter cation.…”

“…52,61 It is particularly notable that the complex [PPh 4 ] 2 [(UO 2 ) 2 (C6) 3 ] was obtained with NMP as cosolvent but, notwithstanding the closeness of C6 2− and muc 2− ligands, NMP does not coordinate in this case. 52 Complex 2 does not have the U/dicarboxylic acid stoichiometry of the reaction mixture designed to give rise to an anionic coordination polymer and its actual 1 : 1 U/dicarboxylate stoichiometry is that of a neutral species requiring no counter cation. That this is due to the resistance of the NMP solvent to hydrolysis and thus to any buffering at a higher pH than the initial value that can occur with DMF is indicated by the successful isolation of an anionic polymer from a mixture with the same 2 : 3 U : dicarboxylic acid ratio in complex 4 (see below) though this synthesis provides yet another example of the effectiveness of dimethylammonium ion in crystallising such a polymer, thus leaving the alternative counter-cation, [Co(en) 3 ] 3+ , in solution.…”

“…1, the formate ligand derived from DMF hydrolysis serves to convert what would otherwise be a neutral [UO 2 (muc)] unit into one that is anionic and has a role somewhat different to that in most related species. In particular, formate is not present in the uranyl muconate complex obtained with DMF as cosolvent in the presence of [Ni(bipy) 3 ] 2+ (bipy = 2,2′-bipyridine), 52 nor in any of a series of complexes with saturated dicarboxylate ligands Cn 2− with n = 7, 8, 9, 10, 12 and 13, also obtained with DMF as cosolvent and diverse combinations of metal cations and bipy or phen ligands (some of these complexes including oxo anions). 39,[53][54][55][56] Although none of the latter complexes involves Zn II cations, it seems difficult to rationalise this difference (see Table 2 for an overview of all these species).…”

“…The extended muconate ligand being essentially planar, these strands have a distinctly nearly planar, zigzag shape, and they lie side-by-side to give planar sheets parallel to (101 ¯). Each strand can be seen as part of the diperiodic, near-planar array known in the complex [Ni(bipy 52 but in 1 the cations lie in sheets between those of the anions rather than within the same plane as in the latter complex. Part of the reason for greater segregation in complex 1 may be the larger size of the phen units compared to those of bipy, which appears to result in more obvious parallel-displaced π-stacking interactions between the cations [centroid⋯centroid distances, 3.4928(12) and 3.9011(12) Å; dihedral angles, 1.06 (10) and 0°; slippage 1.04 and 2.02 Å].…”