Tetraaqua metal squarate complexes, M(C 4 O 4 )(H 2 O) 4 , (M ) Fe, Co, Ni, Zn), are known to have a polymeric chain structure with C 4 O 4 2as a bridge (µ-2) ligand between two metal ions in the trans position. Each metal ion is bonded to two C 4 O 4 2and four water molecules. They are all isostructural with space group C2/c. A complete Ewald sphere of data is measured at 120 K up to 2θ of 100-120°using Mo KR radiation for each complex. Such carefully measured intensities are used to investigate the detailed electron density distribution in order to understand the chemical bonding and the d-orbital splitting of the metal ions subjected in such a ligand field. Results on the electron density distribution will be presented in the form of deformation density and of Laplacian maps. Deformation density will be presented in terms of experimental ∆F x-x , ∆F m-a (multipole model), and of theoretical ∆F derived from the HF and DFT calculations. The interesting bent bond feature on the four-membered ring ligand C 4 O 4 2is explicitly demonstrated by the deformation density distribution and the bond path of the cyclic carbon-carbon bond. The asphericity in electron density distribution around the metal ion is also clearly illustrated in these compounds both in the deformation density and in Laplacian of the density. The comparison on the series of 3d-transition metal complexes will be made not only by the deformation density distribution and by the Laplacian of the density but also by the d-orbital population and by the associated topological properties at the bond critical point. The total number of d-electrons from the experiments are 6. 05, 6.88, 7.89, and 8.40, respectively, for Fe(II), Co(II), Ni(II), and Zn(II) ions in these compounds. A comparison between experiment and theory is made for the Ni complex.

This work illustrates the structural relationship between three types of metal squarates as well as the ligand in its acid form and in its monoanion salt. Squaric acid, H2C404, is known to have a polymeric layer structure with planar molecules connected through intermolecular hydrogen bonds. The interlayer distance is only 2.649A. The crystal of H2NMe2[H3(C404)2] is found to contain columns of [H3(C404)2-] repeating units, again connected by intermolecular hydrogen bonds. Within the repeated unit, there is a symmetric hydrogen bond connected to two HC404 moieties. A new type of metal squarate with M(HCaOa)2(H20)4 [_M : MnU~ Fe n both belong to space group P1, Z-1, a = 5.194 (3), b = 7.454(2), c = 8.901(2)A, u = 67.07(2), /3 = 77.26(3), y = 74.46(4) °, for Mn u] is shown to have a layer-type structure, where all [HC404] units are bonded into infinite chains via symmetric hydrogen bonds, each (HC404)22-ligand bridging two metal ions (#-2) in a trans fashion. The structurally most well understood metal squarate M(CaOa)(H20)4 (M = Mn u, Fe u, Co u, Ni il and Zn u, space group C2/c, Z = 4) is again a polymeric chain with C4042serving as a bridging ligand between two metal ions (#-2) in trans positions. A threedimensional polymeric structure is found to have the formula M(C404)(H20)2, where C40 ]-is a bridging ligand between four metal ions (#-4). Due to the slight difference in packing, there are two structure types in this category: one is in space group R3 [M = Fe u, a = 11.440 (2), c = 14.504 (3) A,oZ = 9], the other is in Pn3n [M = Co u, a = 16.255 (3)A, Z = 24]. The structural relationship between all these structures relies heavily on the understanding of intra-and intermole-, cular hydrogen bonds. The interesting building blocks of each compound will be illustrated. There are tunnels of various sizes in all these structures.

A small peptide mimetic molecule can form diverse nanostructures such as nano-vesicles, nano-tubes and nano-ribbons/fibrils by self-assembly, in response to various physical and chemical stimulations.

Complex [Na(phen)(3)][Cu(NPh(2) )(2)](2), containing a linear bis(N-phenylanilide)copper(I) anion and a distorted octahedral tris(1,10-phenanthroline)sodium counter cation, has been isolated from the catalytic C-N cross-coupling reaction with the CuI/phen/tBuONa (phen=1,10-phenanthroline) catalytic system. Complex 2 can react with 4-iodotoluene to produce 4-methyl-N,N-diphenylaniline (3 a) with 70.6 % yield. In addition, 2 can work as an effective catalyst for C-N coupling under the same reaction conditions, thus indicating that 2 is the intermediate of the catalytic system. Both [Cu(NPh(2))(2)](-) and [Cu(NPh(2))I](-) have been observed by in situ electron ionization mass spectrometry (ESI-MS) under catalytic reaction conditions, thus confirming that they are intermediates in the reaction. A catalytic cycle has been proposed based on these observations. The molecular structure of 2 has been determined by single-crystal X-ray diffraction analysis.

Complex [K3(phen)8][Cu(NPh2)2]3 (1, phen = phenanthroline) was isolated from the catalytic C-N cross coupling reaction based on the CuI-phen-tBuOK catalytic system. Complex 1 can react with 4-iodotoluene to give 4-methyl-N,N-diphenylaniline (3a) in 50% yield (based on all available NPh2(-) ligands of complex 1). In addition, 1 can also work as an effective catalyst for the C-N coupling reactions under the same reaction conditions, indicating that 1 may be an effective intermediate of the catalytic system. In the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), a radical scavenger, the stoichiometric reaction between complex 1 and 4-iodotoluene was significantly quenched to give a low yield of 12%. The results suggest that the radical path dominates in the reaction, with (phen)KNPh2 as the possible radical source. The structures of 1 and (phen)KNPh2 were both determined by single crystal X-ray diffraction studies.