Diamondoid network

The three-dimensional network structure of diamond can be considered as constructed from the linkage of nodes (C atoms) with rods (C-C bonds) in a tetrahedral pattern. From the viewpoint of crystal engineering, in a diamondoid network the node can be any group with tetrahedral connectivity, and the linking rods (or linker) can be all kinds of bonding interactions (ionic, covalent, coordination, hydrogen bond, and weak interactions) or molecular fragment. 

The molecular skeletons of adamantane, (CH2)6(CH)4, and hexamethylenetetramine, (CH2)6N4 (Fig. 20.4.1) constitute the characteristic structural units of diamondoid networks containing one and two kinds of four-connected nodes, respectively. If the rod is long, the resulting diamondoid network 

Some crystalline compounds that exhibit diamondoid structures are listed in Table 20.4.1. The rod linking a pair of nodes can be either linear or nonlinear. 

In the crystal structure of ice-VII, which is formed under high pressure, the node is the O atom, and the rod is a hydrogen bond. Since the H atoms are disordered, the hydrogen bond is written as O- H- O in Table 20.4.1, indicating equal population of O-H- O and O- H-O. The degree of interpenetration is two, as shown in Fig. 20.4.3. 

Compound Node Linking rod Bond type Degree of Remarks 

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Figure 8.75 (a) Diamondoid networks and their components. Normal ice Ih has a hexagonal arrange-... 

In designing ever larger diamondoid networks, it is important to retain the approximate T(i symmetry of the building blocks. This may be achieved via a single self-complementary building block such as 8.59 which possesses four mutually complementary carboxylic acid groups, or by a modular approach, which uses a combination of a TA (or at least, S 4) node such as the cubeane cluster [Mn(CO)3( j,3-OH)] 4 (8.60) and a linear spacer (A-A) (Figure 8.76). 

The self complementary 8.59 may be regarded as the logical three-dimensional progression of the topological zero-, one- and two-dimensional points, chains and sheets formed by benzoic acid, tereph-thalic acid and trimesic acid (Section 7.4.1), shown schematically in Figure 8.77. Adamantane-1,3,5,7-tetracarboxylic acid (8.59) forms a diamondoid network with cavities so large that close packing can... 

Figure 8.76 Construction of diamondoid networks via self-assembly of self-complementary 54 building blocks or modular self-assembly of mutually complementary 54 nodes and linear spacers.

Carlucci, L., Ciani, G., Proserpio, D. M., Rizzato, S., Three novel interpenetrating diamondoid networks from self-... 

In the crystal structure of CU2O, each O atom is surrounded tetrahedrally by four Cu atoms, and each Cu atom is connected to two O atoms in a linear fashion. Hence the node is the O atom, and the rod is O-Cu-O. Figure 20.4.2 shows a single CU2O diamondoid network, and the crystal structure is composed of two interpenetrating networks. 

Figures 20.4.4(a) and 20.4.4(b) illustrate the crystal structure of the 1 1 complex of tetraphenylmethane and carbon tetrabromide. The nodes comprise C(C6H5)4 and CBr4 molecules, and the each linking rod is the weak interaction between a Br atom and a phenyl group. The hexamethylenetetramine-like structural unit is outlined by broken lines. Figures 20.4.4(c) and 20.4.4(d) show the crystal structure of tetrakis(4-bromophenyl)methane, which has a distorted diamondoid network based on the hexamethylenetetramine building unit. If the synthon composed of the aggregation of four Br atoms is considered as a node, then two kinds of nodes (Br4 synthon and quatenary C atom) are connected by rods consisting of p-phenylene moeities.

Crystal structure of CU2O (a) single diamondoid network and (b) two interpenetrating networks. 

Hexamethylenetetramine-like structure unit in the diamondoid network of... 

In the complex [Cu(L)4]PF6 (L = 3-cyano-6-methylpyrid-2(lH)-one), the hydrogen-bonded linkage involves the amido R2(8) supramolecular synthon [Fig. 20.4.15(a)]. Each Cu(I) center serves as a tetrahedral node in a fourfold interpenetrated cationic diamondoid network. The tetrahedral metal cluster [Mn(/z3-OH)(CO)3]4 can be used to construct a diamondoid network with the linear 4,4/-bipyridine spacers [Fig. 20.4.15(b)],... 

N. R. Organically templated three-dimensional open-framework metal selenites with a diamondoid network. J. Mater, Chem. 2003. 13, 1635-1638. (d) Behera, J. N. Ayi, A. A.. Rao. C. N. R. The First Organically Templated Open-Framework Metal Selenate with a Three-Dimensional Architecture. Chem. Commun. 2004, 456-457. 

Figure 20 Part of the four-fold interpenetrated 3D diamondoid network formed by [Cu(L)4]+ [L = 3-cyano-6-methylpyrid-2(l//)-one] as its PF6 salt [58], Hydrogen-bonded links are provided by R2(8) synthons involving all amide groups. Oxygen, nitrogen and key hydrogen atoms are shaded.

These approaches and their differences are well illustrated if one considers the subject of diamondoid networks. 

The use of transition metals or transition metal clusters to act as nodes for the modular self-assembly of diamondoid networks that are sustained by coordinate covalent bonds is also well established. Such architectures are of more than aesthetic appeal. Indeed, such structures have resulted in a class of compound with very interesting bulk and functional properties. Metal-organic diamondoid structures in which the spacer moiety has no center of inversion are predisposed to generate polar networks since there would not be any inherent center of inversion. Pyridine-4-carboxylic acid is such a ligand and bis(isonicotinato)zinc exists as a three-fold diamondoid structure that is thermally stable and inherently polar.33... 

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