Nets, interpenetrating plane

Fig. 11 (Top) Perspective view of an [Fe]4 rhombus in the [Fe(bpe)2(NCS)2]-CH3OH 2D polymer. (Bottom) Schematic representation of the interpenetration of a layer lying in the plane of the sheet and three orthogonal layers (left). Perspective view of the crossing of two independent net systems defining the rectangular channels (right). Balls and sticks represent iron atoms and bpe ligands, respectively...

In the inclined mode of interpenetration any one sheet has an infinite number of inclined ones passing through it to produce an interlocked 3D composite in the manner represented in Figure 16. In contrast to parallel interpenetration, each sheet passes through an inclined one just once along a line of intersection of the two planes. All examples of inclined interpenetration known at present involve either (4,4) or (6,3) nets. 

In principle (4,4) nets in three mutually perpendicular planes could interpenetrate as considered in reference 1, but no examples of this are known at present. 

Class II (Non-translational) The individual nets are related by means of space group symmetry elements, mainly inversion centers, but also proper rotational axes, screw axes and glide planes. The degree of interpenetration Z corresponds to the non-translational degree Zn, i.e. the order of the symmetry element that generates the interpenetrated array from the single net. In almost all cases Zn is 2, but a few examples with Zn up to 4 are known. 

Fig. 10 (a) Coordination environment of Co, showing the building unit of [Co3(bpdc)3(bpy)] (8). (b) Packing diagram of one of the two nets of 8 viewed down the b axis, (c) Twofold interpenetrating 3D networks viewed down the a axis, (d) Space-filled model of 8 viewed perpendicular to the (001) plane... 

As for ID nets, there are a number of different ways for 2D networks to interpenetrate. The compound Ag(tcm) (tern = tricyanomethanide),C(CN)J is a coordination polymer composed of 2D chicken-wirelike (6,3) networks. The networks are corrugated and interpenetrate such that discrete layers of doubly interpenetrating networks are formed (Fig. 2a). The mean planes of the interpenetrating sheets in each layer are parallel and coincident, and the topology of interpenetration can be described as 2D 2D parallel interpenetration. The topology of interpenetration can and should be described further (see Ref. [1] for further descriptions of different possible interpenetration topologies). 

When the mean planes of the interpenetrating networks are parallel but no longer coincident, an overall 3D entanglement is achieved (2D 3D parallel interpenetration). An example of this is the structure of Cu4(dca)4-(bipy)3(MeCN)2 [dca= dicyanamide, N(CN)2, bipy= 4,4 -bipyridine]. Each coordination network is polymeric in only two directions but has a certain "thickness in the third. Each net is penetrated by four others that are parallel but offset in the third, nonpolymeric direction. Two layers penetrate the first toward the edges of the layer (one on either side), and two others penetrate toward the middle of the layer (again, one each propagating out either side). Each layer is identical and thus, a 3D entanglement results. 

Pearson (1984) noticed that the ThMni2 structure contains two interpenetrating kagome nets of Mn atoms that lie in the (100) and (010) planes. The nets are not planar since atoms located in the 8(i) and 8(j) positions have x-parameters of 0.275-0.284 (see table 2 for the uranium aluminides and the RFeioV2 compounds) instead of 0.250 for the ideal planar case. 

The first aspect is that networks can interpenetrate such that their mean lines of propagation (or mean planes in the case of 2D nets) can either be aU parallel or be inclined at two or more angles to each other. The second aspect is that the interpenetration can lead to overall entanglements that are either of the same dimension as the individual nets or of higher dimensions. The latter case is sometimes referred to as polycatenation (as opposed to interpenetration) however, here we refer to both cases as interpenetration as they both clearly fall under the definition given above. 

In this structure, the individual nets have a ID ladder topology, but with three legs to the ladder instead of two (a double ladder ). The mean directions of propagation are all parallel (and hence it is parallel interpenetration), but the mean planes are inclined, which allows the interpenetration (Figure 4). 

Similarly to ID nets, 2D nets can interpenetrate in either a parallel or inclined manner, leading to overall entanglements that are either 2D or 3D in nature. A classic example of 2D-> 2D parallel interpenetration is the structure of [Ag(tcm)], tcm = tricyanomethanide (C(CN)3 ). This structure contains pairs of interpenetrating (6,3) nets in which the mean planes of each... 

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