Q notation

The Q notation used above is not sufficient to describe the basic building units in a/uminosilicates. While in framework silicates the environment of each silicon atom is always Q4(4Si), in framework aluminosilicates there are five possibilities described by the formula Q4[nAl, (4 — n)Si], where n = 0,1, 2, 3, or 4. We shall for simplicity denote these five basic units as Si(nAl)... 

Here, the modified Q notation, Q"W,A10 is applied, where n denotes the number of connected tetrahedral phosphate, m gives the number of aluminate species connected to a central phosphate unit and x specifies the nature of the bonded aluminate spedes (i.e. 4, 5 or 6 coordinate aluminium). 

Q notation specifies the number of oxygens of the SiO/ unit bridging to other Si (or Al) atoms (e.g., a Q silicate has three bridging and one nonbridging oxygen per silicate tetrahedron). 

In the Si MAS NMR spectrum (Fig. 1) two signals are observed at the chemical shifts -112 ppm (Q ) and -104 ppm (Q ). The signal at -93 ppm shows the groups at a very small intensity. For identifying the silicon atoms the Q notation is used. Q is a silicon atom bonded to four oxygen atoms in a tebahedral environment. The superscript denotes that n oxygen atoms were connected to fiirdier silicon atoms (Scheme 2). 

Figure 4. Comparison of 29Si NMR spectra of an add-catalyzed TEOS sol (H.20/Si = 2) and a commercial aqueous silicate (Ludox HS40) (a) TEOS sol after 3 h (b) TEOS sol after 3 days (c) TEOS sol after 14 days of reaction and (d) Ludox sol. Q notation refers to the number of bridging oxygens (-OSi) surrounding the central silicon atom (0-4). From Assink (41).

The hypothesis of pure precession (Van Vleck, 1929) is often used in the estimation of A-doubling constants. These constants, in the o,p, q notation suggested by Mulliken and Christy (1931), are introduced into the effective Hamiltonian... 

Q, Q notation conventionally used to denote a linear quadrupole m/z filter subscripts (usually n = 1 or 3) are sometimes used to distinguish between two such devices, e.g., as incorporated into a triple quadrupole instrument. 

In Q notation, the superscript n denotes the number of bridging oxygens (-OSi) surrounding the central silicon, and the sum of the subscripts, x, equals the number of silicons comprising the silicate species, e.g., dimer ( jr = 2), trimer ( . x = 3), etc., where Q" species without subscripts are counted as x = 1. 

The Q notation indicates silicon tetrahedrally coordinated by four oxygens. The superscript gives the number of coordinated oxygens which are part of siloxy bridges. 

NMR. The Q-notation (8) was used to identify the silicic acid ester structures. The superscript on the Q-unit represents the number of siloxane bonds (-OSi) attached to the silicon under consideration. The subscript 4c identifies the silicon as being contained in a cyclotetrasiloxane ring composed of 4 Si04 tetrahedra. The assignments for the resonances were made by comparison with literature data (9, 10). 

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