Quaternary co-crystals

Figure 2.13 Hydrogen-bonded unit within the quaternary co-crystal cyclohexane-1,3,5-tricarboxylic acid l,2-bis(4-pyridyl)ethane l,4-bis(4-pyridyl)butane ortAo-xylene (2 2 1 ). The ortAo-xylene molecules are disordered in cavities formed by the hydrogen-bonded components.

Moreover, it is reported that the chiral co-crystals of a quaternary ammonium salt were formed from an equimolar solution of achiral carboxylic acid and amine components [96,97]. These crystals belong to a chiral space group, and have both clockwise (P) and counterclockwise (M) helicities. 

Luthra, S. A. Casteel, M. Frericks-Schmidt, H. Krzyzaniak, J., In-situ reactivity of API and excipients in an aqueous oral formulation resulting in formation of a quaternary supramolecular co-crystal complex. In AAPS, Washington, DC, October 25, 2011. 

Quaternary ammonium ions have long been known to act as stmcture-directing agents in the crystallization of zeolites <1961JCS971 >. Millini and co-workers have more recently employed the azoniaspiro compounds 154,9, and 155 for this reason to produce novel microporous frameworks <1998MI199>. 

The crystal standard of (7r-cp)2Ti(NCO)2 has been determined and confirms that, in the solid state, the cyanate group is here N-bonded it was only in the last stages of the analysis that the 0-bonded alternative could be finally eliminated (i). Hexa-iV-cyanato complexes of ytterbium, erbium, and neodymium have been reported as quaternary onium salts (16) and reference made to the series of tetraethylammonium salts of [Ln(NCO)0] (Ln = Eu-Yb) (22) these results extend Table XLII. The ESR spectra of series of complexes CuL2(NCO)2 (L = an, or substituted an) have been interpreted to show Cu— N(CO)—Cu bridges with no indication of any Cu-0 interactions (19). The ESCA spectra of [M(NCO)4] (M = Mn, Co, Zn) have been recorded (12). 

Olofson and co-workers28 obtained evidence for homoaromaticity of the l,l,4-trimethyl-l,4-dihydro-l,2,4,5-tetrazinium cation (23) from a crystal-structure determination. The quaternary nitrogen N-l is tetrahedral, causing the ring to assume the boat shape. There is evidence for substantial delocalization of the N-4 electron pair (hybridization between sp2 and sp3), whereas N-l is 0.51 A, while N-4 is only 0.26 A above the N-2—C-3—N-5— C-6 plane. It should be noted that the crystal structures of 22 and 23 have remarkable similarities. Both molecules are in the boat conformation with their prows twice as high as their sterns. Also, carbons occupy these apices in... 

Four crystal structures of Ni CODHs have been determined from the following organisms C. hydrogenoformans [87,88], Rhodospirillum (R.) rubrum [89] and the bifunctional CODH/ACS from M. thermoacetica [90,91]. In each case CODH has a very similar homodimeric quaternary structure with a diameter of about 100 A in the largest dimension and a total of five FeS clusters (Fig. 3A). An initially unexpected [4Fe - 4S] center, now called the D-cluster, is coordinated by the two subimits very close to the molecular surface. Each subunit also binds an additional [4Fe-4S] center, called the B-cluster, as well as the catalytic Ni-containing C-cluster. There is an electron transfer pathway between the physiological redox partner, the exposed D-cluster, then the B-cluster of one subunit and finally the C-cluster of the other subunit. The electron flow direction will depend on whether the enzyme reduces CO2 or oxidizes CO (Eq. 2). 

Ternary and quaternary metal oxides of perovskite and related structures can be prepared by employing hydroxide, nitrate and cyanide solid-solution precursors as well [5]. For example, Ln, M (OH)3 (where Ln=La or Nd and M=Al, Cr, Fe, Co or Ni) and La, 3,M M (OH>3 (where M=Ni and M =Co or Cu) crystallizing in the rare-earth trihydroxide structure are decomposed at relatively low temperatures (-870K) to yield LaNiOj, LaNij po, P3, LaNij CUj P3 etc. 

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