Ni(2,2′:6′,2″-Terpyridine-4′-carboxylate)₂ Zwitterions and Carboxylate Polyanions in Mixed-Ligand Uranyl Ion Complexes with a Wide Range of Topologies

Abstract

The zwitterionic complex formed by Ni II and 2,2ʹ:6ʹ,2-terpyridine-4ʹ-carboxylate, Ni(tpyc)2, has been used as a coligand with a diverse group of polycarboxylates in uranyl ion complexes synthesized under solvohydrothermal conditions, thus giving a series of 14 mixed ligand, heterometallic compounds. Bothcyclohexanedicarboxylate and tdc 2is 2,5-thiophenedicarboxylate, display discrete U4Ni2 dinickelatetrauranacycles, a motif which is also found as part of a daisychain coordination polymer in [(UO2)4(bdc)3Ni2(tpyc)4(NO3)2]2CH3CN2H2O (3), where bdc 2is 1,4-benzenedicarboxylate. Similar U4Ni2 rings associate to form a nanotubular polymer in [(UO2)2(tca)Ni(tpyc)2(NO3)]2CH3CN2H2O (4), where tca 3is tricarballylate. [(UO2)2(1,2-pda)(1,2-pdaH)Ni(tpyc)2(NO3)]CH3CN (5), where 1,2-pda 2is 1,2phenylenediacetate, crystallizes as a meander-like chain in which each bent section can be seen as an open, semi-U4Ni2 ring. Oxalate (ox 2-) gives [(UO2)2(ox)2Ni(tpyc)2] (6), a monoperiodic polymer containing smaller U4Ni rings, while 1,2,3-benzenetricarboxylate (1,2,3-btc 3-) and citrate (citH 3-) give [Ni(tpycH)(H2O)3][UO2(1,2,3btc)]22H2O (7) and [UO2Ni2(tpyc)4][UO2(citH)]2 (8), two complexes with charge separation, the latter displaying 1D + 2D semi-interpenetration. [(UO2)2(btcH)Ni(tpyc)2(NO3)] (9) and [(UO2)2(cbtcH)Ni(tpyc)2(NO3)] (10), where btc 4and cbtc 4are 1,2,3,4-butanetetracarboxylate and cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate, respectively, are diperiodic networks with hcb topology, and [(UO2)2(ndc)Ni(tpyc)2(OH)(NO3)] (11), where ndc 2is 2,6-naphthalenedicarboxylate, is a sql network containing dinuclear nodes and involving 100-membered U10Ni4 metallacyclic units. U4Ni2 rings are found in the diperiodic polymer formed in [(UO2)4(t-R-1,2-chdc)4Ni2(tpyc)4] (12), where t-R-1,2-chdc 2is trans-R,R-1,2-cyclohexanedicarboxylate, the heavily puckered sheets being interlocked. 1,3-Phenylenediacetate (1,3-pda 2-) gives a very thick diperiodic polymer with KIa topology, [(UO2)4(1,3-pda)4Ni2(tpyc)4]CH3CN2H2O (13). A triperiodic framework is formed with nitrilotriacetate (nta 3-) in [(UO2)2(nta)2Ni2(tpyc)2] (14), where Ni II is found in Ni(tpyc)2 units as well as in Ni(nta)2 4moieties which both act as 4-coordinated nodes.

Zwitterionic and Anionic Polycarboxylates as Coligands in Uranyl Ion Complexes, and Their Influence on Periodicity and Topology

“…In contrast, the pyridinium rings are nearly parallel to the mean plane of the molecule and they form weaker, intersheet interactions [centroid···centroid distance, 4.217(3) Å; dihedral angle, 16.1(2)°]. Larger discrete hexanuclear rings, devoid of the internal partition found here, were also found in the uranyl ion complexes with a combination of Ni­(tpyc) 2 zwitterions and either cis -1,2-cyclohexanedicarboxylate or 2,5-thiophenedicarboxylate, and they were also found as motifs present in coordination polymers, but in these cases, the bulky and rigid zwitterionic species is linear while the anionic dicarboxylates provide the curved parts of the ring.…”

“…While these results confirm that pL1 is a good mimic of an anionic dicarboxylate in its capacity to form coordination polymers, the adoption of a bis(κ 1 O) binding mode may be indicative of a significantly weaker carboxylate donor capacity than that of an anionic species, as previously noted in the case of the Ni(tpyc) 2 zwitterionic ligand. 1 In the case of complex 4, where one of the formate ligands is bound in a κ 1 O manner with a U1−O9 bond length of 2.2948(16) Å, the two bonds to pL1 with lengths of 2.3700 (14) and 2.3678 (14) Å are significantly longer, suggesting that indeed the zwitterion is a weaker donor. However, in complexes 2 and 3, where the U VI centers are both in hexagonal-bipyramidal coordination, the bond lengths with pL1 of 2.374(3) and 2.4168(13) Å, respectively, also differ significantly, indicating coligand effects which render the generality of the conclusion drawn for complex 4 uncertain.…”

“…Systematic attempts at complex synthesis with each zwitterionic ligand and with each anionic polycarboxylate (and some others that did not give any crystalline material) were made, and the 15 complexes reported are the only ones for which single crystals suitable for structure determination were obtained. While attempts at the synthesis of uranyl ion complexes with two different anionic polycarboxylates as ligands are most often unsuccessful, incorporation of both zwitterionic and anionic polycarboxylates in the same species appears to be relatively straightforward, with the present zwitterionic ligands as well as with Ni­(tpyc) 2 , making this a reliable method for modifying the structures formed by a given anionic polycarboxylate.…”

“…Elemental analyses of the zwitterionic ligands were performed using an Elementar Vario Micro Cube. 1 H NMR spectra (in D 2 O) were recorded on a JEOL ECZ400 spectrometer, and they are given in Figure S1 (Supporting Information). 1,4-Bis(bromomethyl)-2,3,5,6-tetramethylbenzene and 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene were prepared according to the literature.…”

“…In exploring the coordination chemistry of the zwitterionic dicarboxylate Ni­(tpyc) 2 (tpyc – = 2,2′;6′,2″-terpyridine-4′-carboxylate) as a reinforcing and modifying bridge within coordination polymers formed by anionic dicarboxylates with uranyl ion, , as an extension of the widespread use of polycarboxylates in uranyl chemistry, − we were drawn to conclude that the zwitterion does provide a versatile coligand and that its functions depend upon both its essentially linear form and the interactions induced by its terpyridine core. This form and these interactions appeared to result in the formation of discrete heterometallacyclic units as well as mono- or diperiodic polymers, many of the latter showing significant solvent-accessible free space and thus the potential for accommodation of reactive guests, but in no case was a fully enclosed cavity identified.…”