Lan-Sun Zheng

A Chiral 60-Metal Sodalite Cage Featuring 24 Vertex-Sharing [Er4(μ3-OH)4] Cubanes

A chiral, cagelike, high-nuclearity lanthanide hydroxide cluster containing 60 Er(III) ions is reported. The cluster core possesses a fascinating sodalite-like structure with 24 vertex-sharing cubane-like [Er(4)(mu(3)-OH)(4)](8+) units. The hexagonal face of the sodalite cage features a templating mu(6)-CO(3)(2-) ion. Magnetic studies revealed weak antiferromagnetic interactions.

Keeping the Ball Rolling: Fullerene-like Molecular Clusters

The discovery of fullerenes in 1985 opened a new chapter in the chemistry of highly symmetric molecules. Fullerene-like metal clusters, characterized by (multi)shell-like structures, are one rapidly developing class of molecules that share this shape. In addition to creating aesthetically pleasing molecular structures, the ordered arrangement of metal atoms within such frameworks provides the opportunity to develop materials with properties not readily achieved in corresponding mononuclear or lower-nuclearity complexes. In this Account, we survey the great variety of fullerene-like metal-containing clusters with an emphasis on their synthetic and structural chemistry, a first step in the discussion of this fascinating field of cluster chemistry. We group the compounds of interest into three categories based on the atomic composition of the cluster core: those with formal metal-metal bonding, those characterized by ligand participation, and those supported by polyoxometalate building blocks. The number of clusters in the first group, containing metal-metal bonds, is relatively small. However, because of the unique and complex bonding scenarios observed for some of these species, these metalloid clusters present a number of research questions with significant ramifications. Because these cores contain molecular clusters of precious metals at the nanoscale, they offer an opportunity to study chemical properties at size ranges from the molecular to nanoscale and to gain insights into the electronic structures and properties of nanomaterials of similar chemical compositions. Clusters of the second type, whose core structures are facilitated by ligand participation, could aid in the development of functional materials. Of particular interest are the magnetic clusters containing both transition and lanthanide elements. A series of such heterometallic clusters that we prepared demonstrates diverse magnetic properties including antiferromagnetism, ferrimagnetism, and ferromagnetism. Considering the diversity of their composition, their distinct electronic structures, and the disparate coordination behaviors of the different metal elements, these materials suggest abundant opportunities for designing multifunctional materials with varied structures. The third type of clusters that we discuss are based on polyoxometalates, in particular those containing pentagonal units. However, unlike in fullerene chemistry, which does not allow the use of discrete pentagonal building blocks, the metal oxide-based pentagonal units can be used as fundamental building blocks for constructing various Keplerate structures. These structures also have a variety of functions, including intriguing magnetic properties in some cases. Coupled with different linking groups, such pentagonal units can be used for the assembly of a large number of spherical molecules whose properties can be tuned and optimized. Although this Account focuses on the topological aspects of fullerene-like metal clusters, we hope that this topical review will stimulate more efforts in the exploratory synthesis of new fullerene-like clusters. More importantly, we hope that further study of the bonding interactions and properties of these molecules will lead to the development of new functional materials.

A four-shell, 136-metal 3d-4f heterometallic cluster approximating a rectangular parallelepiped

A nanosized heterometallic cluster containing 60 La(III) and 76 Ni(II) ions, which are arranged into a four-shell, nest-like framework structure, was obtained by the hydrolytic reaction of the mixed La(NO(3))(3)-Ni(NO(3))(2) system using iminodiacetate as an ancillary ligand to control the hydrolysis.

Dual Shell-like Magnetic Clusters Containing NiII and LnIII (Ln = La, Pr, and Nd) Ions

Dual shell-like nanoscopic magnetic clusters featuring a polynuclear nickel(II) framework encapsulating that of lanthanide ions (Ln = La, Pr, and Nd) were synthesized using Ni(NO3)(2).6H2O, Ln(NO3)(3).6H2O, and iminodiacetic acid (IDA) under hydrothermal conditions. Structurally established by crystallographic studies, these clusters are [La20Ni30(IDA)30(CO3)6(NO3)6(OH)30(H2O)12](CO3)(6).72H2O (1), [Ln20Ni21(C4H5NO4)21(OH)24(C2H2O3)6(C2O4)3(NO3)9(H2O)12](NO3)9.nH2O [C2H2O3 is the alkoxide form of glycolate; Ln = Pr (2), n = 42; Nd (3), n = 50], and {[La4Ni5Na(IDA)5(CO3)(NO3)4(OH)5(H2O)5][CO3].10H2O} infinity (4). Carbonate, oxalate, and glycolate are products of hydrothermal decomposition of IDA. Compositions of these compounds were confirmed by satisfactory elemental analyses. It has been found that the cluster structure is dependent on the identity of the lanthanide ion as well as the starting Ln/Ni/IDA ratio. The cationic cluster of 1 features a core of the Keplerate type with an outer icosidodecahedron of Ni(II) ions encaging a dodecahedral kernel of La(III). Clusters 2 and 3, distinctly different from 1, are isostructural, possessing a core of an outer shell of 21 Ni(II) ions encapsulating an inner shell of 20 Ln(III) ions. Complex 4 is a three-dimensional assembly of cluster building blocks connected by units of Na(NO3)/La(NO3)3; the structure of the building block resembles closely that of 1, with a hydrated La(III) ion internalized in the decanuclear cage being an extra feature. Magnetic studies indicated ferromagnetic interactions in 1, while overall antiferromagnetic interactions were revealed for 2 and 3. The polymeric, three-dimensional cluster network 4 displayed interesting ferrimagnetic interactions.

Hydrolytic synthesis and structural characterization of lanthanide hydroxide clusters supported by nicotinic acid

Polynuclear lanthanide hydroxide complexes featuring the cubane-like [Ln(4)(mu(3)-OH)(4)](8+) [Ln = Eu(III), Gd(III)] cluster core have been synthesized by controlled hydrolysis of the lanthanide ions using nicotinic acid as the ancillary ligand. The synthetic procedure has been found to significantly influence the nature of the resulting cluster species. In a one-pot synthesis, adjusting the pH of the reaction mixture containing Ln(ClO(4))(3) and nicotinic acid afforded tetranuclear complexes of the general formula [Ln(4)(mu(3)-OH)(4)(Hnic)(5)(H(2)O)(12)](ClO(4))(8) with the [Ln(4)(mu(3)-OH)(4)](8+) (Ln = Eu, Gd) cluster core encapsulated by zwitterionic nicotinate ligands. In stark contrast, mixing aqueous solutions of Ln(ClO(4))(3) and nicotinic acid whose pH had been preadjusted produced assemblies composed of two of the cubane-like cluster cores that are related by a crystallographic inversion center and are doubly bridged by nicotinate ligands using both the carboxylate group and pyridyl N atom for coordination. The influences of pH conditions and synthetic procedures on the identity of the resulting cluster species are discussed, so is the structural relevance of the low-pH complexes to their cluster analogues obtained under higher-pH conditions.

Three-Dimensional Metal-Organic Frameworks Based on Functionalized Tetracarboxylate Linkers: Synthesis, Strucures, and Gas Sorption Studies

New tetracarboxylate ligands with dihydroxy (L(1)) and crown ether functionalities (L(2)) have been synthesized and treated with Cu(II) and Zn(II) ions to generate three-dimensional (3D) metal-organic frameworks (MOFs) with the compositions of [Cu(2)(L(1))(H(2)O)(2)].14DMF.10H(2)O, 5, [Cu(2)(L(2))(H(2)O)(2)].12DMF, 6, [Zn(6)(mu(4)-O)(L(1))(2)(L(1)-H(2))].35DMF.27H(2)O, 7, and [Zn(3)Na(2)(L(2))(2)(DMF)(2)].7DMF.14H(2)O, 8. The four compounds show different framework structures with different connectivities. Compound 5 exhibits the PtS topology whereas compound 6 has a [6(4).8(2)](3)[6(6)] topology. Compound 7 adopts a new [4.6(5)][4(2).6(8)][4(4).6(2)][4(5).6][4(8).6(10).8(3)] topology while compound 8 exhibits the Flu topology. The porosity and H(2) uptake were studied by gas sorption experiments and grand canonical Monte Carlo (GCMC) simulations. Compound 5 shows a high H(2) uptake of up to 1.11 wt % at 77 K.

Ionothermal synthesis of 3d–4f and 4f layered anionic metal–organic frameworks

A La(III)–Co(II) heterometallic framework and a La(III)-based anionic layered architecture were prepared under ionothermal conditions.

Effect of lanthanide contraction on crystal structures of lanthanide coordination polymers with 2,5-piperazinedione-1,4-diacetic acid

A series of lanthanide coordination polymers have been synthesized through the hydrothermal reaction of 2,5-piperazinedione-1,4-diacetic acid (H2PODC) and Ln(NO3)3 (Ln = La, 1; Pr, 2; Sm, 3; Ho, 4 and Er, 5). Crystal structure analysis reveals that their structural variations are attributed to the effect of lanthanide contraction.

Influence of reaction conditions on the channel shape of 3d-4f heterometallic metal–organic framework

Three structural kinds of 3d-4f metal–organic-frameworks (MOFs), {[Ln4(ox)3(Ni(IDA)2)3(H2O)6]}n·xnH2O (Type I: LnLa, Nd, Eu, Gd; IDA = iminodiacetate, ox = oxalate), {[Ln2 (ox)(Ni(IDA)2)2(H2O)2]}n·2nH2O (Type II: LnLa, Pr, Nd, Eu) and {[Dy2(ox)2Ni(IDA)2(H2O)2]}n·2nH2O (Type III), have been synthesized under hydrothermal condition. The crystal structures consist of Ln-oxalate tetramers for Type I, dimers for Type II and one-dimensional polymers for Type III bridged by the metalloligand [Ni(IDA)2]2−. While Type I contains a mixture of “Ln6Ni4-parallelogram” (A-Type) and “Ln6Ni2-parallelogram” (B-Type) channels, Type II and Type III contain only A-type and B-type channels, respectively. A fairly high stability of the MOFs is indicated by thermogravimetric analyses and reversible dehydration and rehydration of guest water molecules, which is confirmed by single crystal-to-single crystal transformation of 1 and 5.

Hydrogen bond induced change of geometry and crystallized form of copper(II) complexes: syntheses and crystal structure of complexes with Schiff-base ligands containing two imidazolyl groups

Copper(II) complexes with the Schiff base methylbis[3-(5-methylimidazol-4-ylmethyleneimino)propyl]amine (BDPA), [Cu(BDPA)][ClO4]2·H2O 1 and [Cu(BDPA)][PF6]22, and with a deprotonated Schiff base ligand [H2BIPOxa0=xa01,3-bis[(5-methylimidazol-4-ylmethyleneimino)propan-2-ol], {[Cu(HBIPO)]ClO4·H2O}n3 and 4, have been prepared. Single-crystal structures show that 1 adopts a distorted square-pyramidal geometry with the basal plane occupied by an imidazole nitrogen, two imines and one amino nitrogen atom and the apical position by another nitrogen atom from BDPA. 2 adopts a distorted trigonal-bipyramidal geometry with two imidazole nitrogen atoms at axial positions. Both 3 and 4 adopt distorted square-pyramidal geometry with four nitrogen atoms from HBIPO in the basal plane and the apical position occupied by a deprotonated imidazole nitrogen atom from an adjacent [Cu(HBIPO)] unit, resulting in polynuclear complexes. The differences in geometry and crystallization pathway between 1 and 2, and 3 and 4, are discussed based on the crystal structures, indicating that hydrogen bonding to the basal plane imidazole group plays an important role both in the change of geometry and crystallization form of the copper(II) complexes.