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The frameworks of zeolites and related crystalline microporous oxide materials, such as aluminophosphates, silicoaluminophosphates and metaloaluminophosphates, are built up of tetrahedrally coordinated (e.g., Si, Al, P) atoms. Microporous structures comprised entirely of octahedral sites are also known, encompassing manganese oxides (OMS materials, Suib 1998) and phases with composition Na2Nb2−xMxO6−x(OH)x•H2O, where M = Ti, Zr, and 0< x ≤ 0.4 (SOMS solids; Nyman et al. 2001, 2002). Mixed octahedral-pentahedral-tetrahedral microporous (OPT) siliceous frameworks have been much studied since the early 1990s (Rocha and Anderson 2000; Anderson and Rocha 2002). Comprehensive research into synthetic OPT materials was initiated by the seminal contributions of Kuznicki (1989, 1990) (titanosilicates ETS-4 and ETS-10), Chapman (1990); Chapman and Roe (1990) (ETS-4, and titanosilicate analogues of minerals vinogradovite and pharmacosiderite) and Anderson et al. (1994, 1995b) (ETS-10), and the early work of the groups of Raveau (Choisnet et al. 1976, 1977) (tantalo and niobosilicates), Corcoran and Vaughan (1989) and Corcoran et al. (1989, 1992) (stannosilicates).
Much research on the synthesis of OPT materials has been inspired and motivated by the many examples of such solids provided by Nature and brought to light by a plethora of mineralogists. As an example, consider the titanosilicate mineral zorite, discovered in 1973 on the Lovozero Tundra (Mer’kov et al. 1973). The structure solution of this mineral was published six years later by Sandomirskii and Belov (1979). Zorite is important because it was one of the first examples of microporous titanosilicates to be prepared in the laboratory (Kuznicki 1989; Chapman 1990; Chapman and Roe 1990). The details of the structure of the synthetic analogue of zorite, known as ETS-4, remained somewhat elusive until a single-crystal x-ray diffraction study …