Structure Mackay

Fig. 2.1 Relationship between the inter-layer spacing and the intra-layer spacing (0-0 distance) in the hexagonal close packed and cubic close packed iron oxide structures (Mackay, 1961, with permission). CR I, CRN Green rust I and II...

It is perhaps worth pointing out that every crystal is in fact defective, even if its only defect is that it has surfaces. However, if a crystal is only a ten-unit-cell cube, about half of the unit cells lie in the surface and thus have environments very different from those of the other half. The physical observation is that very small aggregates need not be crystalline, although they may nevertheless be perfectly structured. Mackay s proposal is to apply the name crystalloid to them. He offered the following definitions [133] ... 

D. H. J. Mackay, in G. D. Easman, ed.. Prediction ofiProtein Structure and the Principles ofiProtein Conformation, Plenum Press, New York, 1989, p. 317. 

The publication of this paper led to a stampede of research, both experimental and theoretical, and an examination of earlier studies by eminent people like Roger Penrose and Alan Mackay in England about the possibilities of filling space by tiling with two distinct populations of tiles, as illustrated in Figure 10.8. This is the basis of quasicrystalline structure. 

A. L. Mackay, J. Klimowski. Towards a grammar of inorganic structure. Comp Math Appl 725 803-824, 1986. 

Fig. 12.2 (a) Polyhedral view of [MnCglAIgGe]. (b) Ball-and-stick view of the shell structure around the [MntglAIgGe] polyhedral cluster. The top and side views are along (001) and (no), respectively. In (c) a Mackay icosahedron in a-MnAI(Si) is oriented along the corresponding directions. 

Hodgkin DC, Kamper J, Mackay M, Pickworth J, Trueblood KN, White JG. Structure of Vitamin B12. Nature 1956 178 64-6. 

Lapierre, C. Pollet, B. MacKay, J. J. Sederoff, R. R. Lignin structure in a mutant pine deficient in cinnamyl alcohol dehydrogenase. J. Agric. Food Chem. 2000, 48, 2326-2331. 

So far, three types of i-QCs appear in the literature Mackay [17], Bergman [18], and Tsai types [19], which have been differentiated on the basis of the polyhedral cluster sequences observed in the respective 1/1 AC structures. These are commonly represented as shown in Fig. 2. An i-QC is concluded to be Mackay-type if its 1/1 AC contains a 54-atom multiply endohedral cluster ordered, from the center out, as a small icosahedron (12 atoms), a larger icosahedron (12), and an icosidodecahe-dron (30). This motif occurs in ACs that consist of transition metals and main-group elements on the right side of the periodic table such as Al-(Pd,Mn)-Si [17,20]. In... 

The discovery of the binary (Yb,Ca)-Cd i-QCs [19] was a remarkable milestone in the history of QCs. The reasons are apparent they offered unique opportunities for structural analyses as they exhibited negligible chemical disorder, probably because of the large differences in the chemical crystallography of the components, in contrast to more common problems with ternary intermetallics. In addition, they also represented new (Tsai) types of AC cores and of i-QCs with a structural motif different from those of the Mackay and Bergman types (above) that were better known at the time. Without doubt, such a breakthrough discovery must lead to an era of related chemical explorations or tunings. Actually, almost all of the i-QC systems developed since 2000 are Tsai types [28,29], including our own additions (below). 

Mackay, D., Paterson, S. (1990) Fugacity models. In Practical Applications of Quantitative Structure-Activity Relationships (QSAR) in Environmental Chemistry and Toxicology. Karcher, W., Devillers, J., Eds., pp. 433 -60, Kluwer Academic Publishers, Dordrecht, The Netherlands. 

Mackay D, Peterson S (1990) In Karcher W, Devillers J (eds) Practical applications of quantitative structure-activity relationships (QSAR) in environmental chemistry and toxicology, Kluwer Academic Publishers, Dordrecht, Holland, p 433... 

Other structural analyses of crystals in which the bifluoride is present are listed in Table 7. One compound, p-toluidinium fluoride [C7H,oN ][HF2 ], is worthy of further comment. The first X-ray diffraction study reported a symmetrical anion (Denne and MacKay, 1971), but a later analysis showed that the proton was not centred between the two fluorines and 7 f h values were 102.5 and 123.5 pm (Williams and Schneemeyer, 1973). This can be explained not by a double minimum potential energy well but by asymmetry due to other forces, such as secondary hydrogen bonding between one end of the bifluoride anion and the N—H group of the cation. An alternative explanation attributes the asymmetry of the bifluoride hydrogen bond to an unsymmetrical crystal field caused by the cation (Ostlund and Bellenger, 1975). 

Akaganeite, P-FeOOH, is named after the Akagane mine in Japan where it was first discovered (Mackay, 1962). It occurs rarely in nature and is found mainly in Cl-rich environments such as hot brines and in rust in marine environments. Unlike the other FeOOH polymorphs, it has a structure based on body centered cubic packing of anions (bcp) (hollandite structure) and contains a low level of either chloride or fluoride ions. It has a brown to bright yellow colour. 

Bernal, J.D. Mackay, A.L. (1965) Topotaxy. Tschermaks mineralogische und petrogra-phische Mitteilungen 10 331-340 Bernal, J.D. Dasgupta, D.R. Mackay, A.L. (1959) The oxides and hydroxides of iron and their structural interrelationships. Clay Min. Bull. 4 15-29... 

Adapted from Mackay et al. (1992) data on indeno[l,2,3-a/]pyrene from Harvey (1997). Structures and their numbering are based on IUPAC recommendations as described by Loening et al. (1990). h U.S. EPA (1998) designation. Exceptions are noted by asterisks. 

Energy calculations for small clusters of atoms indicate that a cluster of 55 atoms should be reasonably stable (Mackay 1962, Allpress and Sanders 1970, Hore and Pal 1972). In addition, calculations suggest that the 55-atom cluster will take up an icosahedral structure in preference to the cubic cuboctahedral structure (Hore and Pal 1972). 

Amot, J.A., Meylan, W., Tunkel, J., Howard, P.H., Mackay, D., Bonnell, M. and Boethling, R.S. (2009) A quantitative structure-activity relationship for predicting metabolic biotransformation rates for organic chemicals in fish. Environ Toxicol Chem, 28, 1168-1177. 

---