Shaoguang Li

Magnesium−Magnesium Bond Stabilized by a Doubly Reduced α-Diimine: Synthesis and Structure of [K(THF)3]2[LMg−MgL] (L = [(2,6-iPr2C6H3)NC(Me)]22−)

A new Mg-Mg-bonded compound stabilized by a doubly reduced alpha-diimine ligand, [K(THF)(3)](2)[LMg-MgL] (L = [(2,6-(i)Pr(2)C(6)H(3))NC(Me)](2)(2-)), has been synthesized and characterized by single-crystal X-ray diffraction and density functional theory analysis. The Mg-Mg bond length is 2.9370(18) A.

Mechanistic Insight into the NN Bond‐Cleavage of Azo‐Compounds that was Induced by an AlAl‐bonded Compound [L2−AlIIAlIIL2−]

An α-diimine-stabilized Al-Al-bonded compound [L(2-)Al(II)-Al(II)L(2-)] (L = [{(2,6-iPr(2)C(6)H(3))NC(Me)}(2)]; 1) consists of dianionic α-diimine ligands and sub-valent Al(2+) ions and thus could potentially behave as a multielectron reductant. The reactions of compound 1 with azo-compounds afforded phenylimido-bridged products [L(-)Al(III)(μ(2)-NPh)(μ(2)-NAr)Al(III)L(-)] (2-4). During the reaction, the dianionic ligands and Al(2+) ions were oxidized into monoanions and Al(3+), respectively, whilst the [NAr](2-) imides were produced by the four-electron reductive cleavage of the N=N double bond. Upon further reduction by Na, the monoanionic ligands in compound 2 were reduced to the dianion to give [(L(2-))(2)Al(III)(2)(μ(2)-NPh)(2)Na(2)(thf)(4)] (5). Interestingly, when asymmetric azo-compounds were used, the asymmetric adducts were isolated as the only products (compounds 3 and 4). DFT calculations indicated that the reaction was quite feasible in the singlet electronic state, but the final product with the triplet-state monoanionic ligands could result from an exothermic singlet-to-triplet conversion during the reaction process.

Tetrahedral Anion Cage: Self‐Assembly of a (PO4)4L4 Complex from a Tris(bisurea) Ligand

Theseanalogies provide promising ideas for the self-assembly ofnovel supramolecular systems based on anion coordination.In the past few decades, zero-dimensional, aestheticallypleasing metal coordination complexes, such as molecularsquares, capsules, tetrahedra, and other complex polyhedralshapes, have attracted much interest.

Chloride Coordination by Oligoureas: From Mononuclear Crescents to Dinuclear Foldamers

A series of acyclic oligourea receptors which closely resemble the scaffolds and coordination behavior of oligopyridines have been synthesized. Assembly of the receptors with chloride ions afforded mononuclear anion complexes or dinuclear foldamers depending on the number of the urea groups.

Sulfate encapsulation in three-fold interpenetrated metal–organic frameworks with bis(pyridylurea) ligands

Self-assembly of two flexible bis-pyridylurea ligands, pentane-1,5-diylbis(3-pyridin-3-ylurea) (L5) and hexane-1,6-diylbis(3-pyridin-3-ylurea) (L6) with ZnSO4 or CdSO4 (metal-to-ligand molar ratio 1 : 2) results in three metal–organic frameworks with (4,4) net structures, {[ML2(H2O)2]SO4·2H2O}n (1: Zn, L5; 2: Cd, L5; and 3: Zn, L6). Single-crystal X-ray diffraction analyses reveal that all the compounds are characteristic of a 3-fold parallel interpenetrated framework with cavities suitable for encapsulating the sulfate anion despite the different spacer lengths ((CH2)5 and (CH2)6) of the two ligands and variation of the metal ions. The ligand adopts an anti–anti conformation and functions as a bridging bidentate linker, while the sulfate ion is selectively bound by four urea functionalities via multiple hydrogen bonds.

Tris Chelating Phosphate Complexes of Bis(thio)urea Ligands

Two bisurea (L(1), L(2)) and one bisthiourea (L(3)) ligands were synthesized and their anion coordination behavior was studied. These ligands can readily form the tris chelates [PO4(L)3](3-) (1, 5, and 6) with phosphate ion (PO4(3-)) in the solid state, in which the anion is coordinated by six urea groups through 12 hydrogen bonds. Solution binding studies by (1)H NMR and UV-vis spectroscopy revealed different binding properties of the ligands toward phosphate ion. While the bis(p-nitrophenyl)-substituted bisurea L(1) retains the 3:1 (host to guest) binding ratio in solution, the diethyl derivative L(2) only forms 1:1 complex with phosphate ion. The more acidic thiourea L(3) undergoes deprotonation/decomposition in the presence of phosphate ion. Moreover, the sulfate complex (2) of L(1) and bicarbonate (3) and carbonate (4) complexes of L(2) have also been obtained, which show lower coordination numbers both in the solid state and in solution.

Coordination polymers and metallomacrocycles based on bis(pyridylcarbamate) ligands with flexible glycol spacers

Six metal–organic coordination polymers or metallomacrocycles, [Zn2Cl4(L2)2]·3H2O (1), [Zn2Br4(L2)2]·0.5H2O (2), {[Cu(L2)2(H2O)2](NO3)2·4H2O·4CH3OH}n (3), [Zn2Br4(L3)2] (4), (ZnBr2L4)n (5) and (ZnBr2L5)n (6), were prepared from zinc(II) or copper(II) salts with flexible bis(pyridylcarbamate) ligands L2 to L5 [L2 = 3-pyridyl-carbamic-acid-oxydi-1,2-ethanediylester, L3 = 3-pyridinyl-carbamic-acid-1,2-ethanediyl-bis(oxy-2,1-ethanediyl)ester, L4 = 3-pyridinyl-carbamic-acid-1,3-propanediylester and L5 = 3-pyridinyl-carbamic-acid-1,4-butanediylester]. Compounds 1, 2 and 4 are hydrogen-bonded 3D porous nanotubular structures composed of metallomacrocycles. Compound 3 has a racemic framework formed by 2D homochiral layers. Compound 5 is a 1D meso-helical chain and 6 is a 1D linear chain, both of which are further connected by N–H⋯O and C–H⋯O hydrogen bonds and π–π interactions into 3D frameworks. The highly flexible bis(pyridylcarbamate) ligands show dramatically different conformations with various metal ions and counteranions, thus leading to the structural diversity of these complexes.

1D → 1D Two-fold parallel interpenetrated coordination polymers with a bis(pyridylurea) ligand

Four unprecedented 1D → 1D interpenetrated (2,4) coordination polymers were obtained from a bis(4-pyridylurea) ligand and octahedral metal ions via catenation of two parallel and collinear 1D ribbons of rings; the ligand L shows an ideal flexibility and adaptability in the formation of these structures.

Coordination polymers derived from a flexible bis(pyridylurea) ligand: conformational change of the ligand and structural diversity of the complexes

The assembly of a bis(pyridylurea) ligand, N,N′-ethane-1,2-diylbis(3-pyridin-4-ylurea) (L), with Zn(AcO)2, CdCl2, CdSO4 or CuSO4 led to four coordination polymers, {[Zn(AcO)2L]·H2O·CH3OH}n (1), {[CdCl2L2]·2DMF}n (2), {[CdSO4L(H2O)3]·3H2O}n (3), and {[CuSO4L(H2O)2]·2H2O}n (4). Compound 1 is an infinite 1D zigzag chain with alternate Zn(AcO)2 units and L molecules. The cadmium(II) dichloro complex 2 features a corrugated sheet structure with a (4,4) net topology, while the sulfato complex 3 shows a unique 1O/2U interwoven 3D structure assembled from zigzag chains. The copper(II) complex 4 is an exceptional diamondoid network with an unusual 12-fold [6 + 6] interpenetration mode. Interestingly, the ligand shows the expected flexibility in the formation of the coordination polymers. In 1, 3 and 4, the central ethylene spacer adopts the anti conformations and is roughly linear, whereas in 2 it assumes a gauche form and exists as a V-shaped linker. The structural variation of these coordination polymers as well as the conformational change of the ligand in the presence of different counter anions and metal ions is discussed.

The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes

By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2 L3 complexes (A represents anion, here orthophosphate PO4 (3-) ), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination-based structures as in transition-metal complexes.