Tetrahedral coordination structures

Figure 5.1 Hexagonal ice structure showing open, tetrahedrally coordinated structure...

Tetrahedral coordination of solvent molecules The final idea checked here is whether incorporating a tetrahedral coordination structure for water molecules in liquid water significantly improves the prediction of cavity formation free energy. We used a cluster Poisson model to accomplish this (Neyman and Scott, 1956). The physical picture is of tetrahedral clusters of water molecules with prescribed intra-cluster correlations but random positions and orientations as suggested in Fig. 8.4. 

Sauvage et al. have synthesized a variety of oligorotaxanes utilizing 1,10-phenanthroline-copper(I) complex [179]. Stable bis(l,10-phenanthroline) copper(I) complex has a tetrahedral coordination structure, and two... 

Some Crystals with Tetrahedrally Coordinated Structures (160) ... 

The well-known affinity of Ag(I) for thioether coordination results in rich coordination chemistry for this ion with 9S3. Reaction of Ag(triflate) with two equivalents of 9S3 in methanol yields [Ag(9S3)2] (Eq. 12a). Despite the propensity of Ag(I) for linear and tetrahedral coordination, structural work [114-116] reveals a six-coordinate Ag(I) complex (Fig. 6 Table 1). The spherical symmetry of this ion and the attendant malleability of its coordination sphere facilitates attainment of six-coordination. The limited bite of 9S3, however, necessitates substantial trigonal elongation of the octahedron (e.g. chelating S-Ag-S angles average 80°). 

The mono-phase model [1, 2, 4, 10, 13] suggests that water contains homogeneous, three-dimensional, tetrahedrally coordinated structures with thermal fluctuations that are random but not quite [4,9]. Unlike the mix-phase model, this mono-phase model explains the freezing expansion at transition as a consequence of the relaxation on the length and angle, in a certain yet unclear manner. 

The MD-movie (Appendix A4-3) shows that in the liquid phase, the H and the O attract each other between the 0 H, but the 0-0 repulsion prevents this occurrence. The intact O-H-O motifs are moving restlessly because of the high fluctuation and frequent switching of the 0 H interactions. Furthermore, the cooperative and ojfj shifts provide further evidence for the persistence of the Coulomb repulsion between the bonding and the non-bonding electron pairs in liquid. Therefore, the H2O in the bulk form of liquid could possess the tetrahedrally coordinated structures with thermal fluctuation [4]. 

Water prefers the monophase of the fluctuated, tetrahedrally coordinated structure with supersolid skin that consists of molecules with fewer than four... 

With known bond lengths (or density) and vibration frequencies, Lagrangian mechanics maps H-bond asymmetric, local, short-range potentials Water and ice prefer statistically the fluctuated, tetrahedrally coordinated structure with supersolid skin despite the fluctuations in 0 H length and <0 H-... 

Things are decidedly different for ionically bonded systems. Generally when an electron leaves a metallic atom to form a cation, the cation will be effectively smaller than the atom in a metallic bond even though the valence electron in the metal is delocalized. Similarly, the size of the anion that has gained the electron is generally larger than the neutral atom. A self-consistent set of ionic radii have been worked out for systems with a coordination number of 6 (rock salt structure). A correction of -1-0.008 nm must be added to the sum of the standard ionic radii for coordination number of 8 and a correction of —0.011 must be subtracted for tetrahedrally coordinated structures. 

D. Weaire, Some properties of random tetrahedrally coordinated structures,... 

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