Structural data, complexes

PDB Research Col-laboratory for Structural Bioinformat-ics (RCSB) macromole-cular structure data on proteins, nucleic acids, protein-nucleic acid complexes, and viruses nu- meric. biblio. -20000 records experi- ments Research Col-laboratory for Structural Bioinformatics online, CD-ROM periodi- cally WU7W.TCsh.0Tg/ pdh/... 

The steps (reactions) by which normal ions fragment are important pieces of information that are lacking in a normal mass spectrum. These fragmentation reactions can be deduced by observations on metastable ions to obtain important data on molecular structure, the complexities of mixtures, and the presence of trace impurities. 

Transition-metal complexes of the thionylimide anion exhibit characteristic vibrations in the regions 1260-1120, 1090-1010 and 630-515 cm , which are assigned to Oas(NSO), Os(NSO) and <5(NSO), respectively. X-ray structural data for several M-NSO complexes reveal N-S and S-O bond lengths of ca. 1.46 0.04 A indicative of double bond character in both of these bonds. 

Oxygen chelates such as those of edta and polyphosphates are of importance in analytical chemistry and in removing Ca ions from hard water. There is no unique. sequence of stabilities since these depend sensitively on a variety of factors where geometrical considerations are not important the smaller ions tend to form the stronger complexes but in polydentate macrocycles steric factors can be crucial. Thus dicyclohexyl-18-crown-6 (p. 96) forms much stronger complexes with Sr and Ba than with Ca (or the alkali metals) as shown in Fig. 5.6. Structural data are also available and an example of a solvated 8-coordinate Ca complex [(benzo-l5-crown-5)-Ca(NCS)2-MeOH] is shown in Fig. 5.7. The coordination polyhedron is not regular Ca lies above the mean plane of the 5 ether oxygens... 

MCl3(NS)(PPh3)2]. In the few complexes for which X-ray structural data are available the M-N-S group is essentially linear (170-177°) (see p. 453 and refs. 233, 235) but spectroscopic data on others suggest that bent and even ij -bridging modes may be possible. 

Numerous solid complexes have been crystallized from brown solutions of iodine and extensive X-ray structural data are available. Complexes of the type L—>-I-X and L—>-I-X-t—L... 

The importance of the proximity effect in cyclodextrin catalysis has been discussed on the basis of the structural data. Harata et al. 31,35> have determined the crystal structures of a-cyclodextrin complexes with m- and p-nitrophenols by the X-ray method. Upon the assumption that m- and p-nitrophenyl acetates form inclusion complexes in the same manner as the corresponding nitrophenols, they estimated the distances between the carbonyl carbon atoms of the acetates and the adjacent second-... 

Table 1.9 summarizes structural data for a number of ruthenium nitrosyl complexes, along with IR data [121, 122],... 

Figure 2.91 Structural data for iridium(III) complexes of dimethylphenylphosphine.

Table 2.14 Structural data for iridium nitrosyl complexes...

Like the isoelectronic Pd2+ and Pt2+, Au3+ exhibits both trans-effects and trans-influence. Table 4.13 (above) lists structural data for a number of complexes AuL3L, showing how the disparity in Au-X distances between cis-and trans-X depends on the position of L in the trans-effect series for the compounds listed, the effect is least noticeable in AuC13NH3 as these two ligands are proximate in the series. 

A number of complexes AuCIL have been made those with cycloalkenes are most stable decomposing at 50-100°C. At present, few structural data are available, an exception being for AuCl(cyclooctene) (Figure 4.42) which has a structure with r/2 bonding of the alkene (Figure 4.43) [183]. 

Table 4. Selected structural data of silylene complexes, substituent effects and pyramidaliza-tion at Si [35-38]...

On the basis of these results it seems to the present author that inner and outer complexes can reasonably be assumed for the electron transfer to the diazonium ion, but that an outer-sphere mechanism is more likely for metal complexes with a completely saturated coordination sphere of relatively high stability, such as Fe(CN) (Bagal et al., 1974) or ferrocene (Doyle et al., 1987 a). Romming and Waerstad (1965) isolated the complex obtained from a Sandmeyer reaction of benzenediazonium ions and [Cu B ]- ions. The X-ray structural data for this complex also indicate an outer-sphere complex. 

Recently Suglobova et al. (3, 4, 5) reported structural data, phase diagrams, and enthalpies of reaction of several complex fluorides of uranium(V) with alkali metals. Their observations indicate that the enthalpy of stabilization represented by the equation... 

This by no means exhaustive discussion may serve to indicate the value of the information provided by magnetic data relative to the nature of the chemical bond. The quantum-mechanical rules for electron-pair bonds are essential to the treatment. Much further information is provided when these methods of attack are combined with crystal structure data, a topic which has been almost completely neglected in this paper. It has been found that the rules for electron-pair bonds permit the formulation of a set of structural principles for non-ionic inorganic crystals similar to that for complex ionic crystals the statement of these principles and applications illustrating their use will be the subject of an article to be published in the Zeitschrift fur Kristallographie. 

While ytterbium(II) benzamidinate complexes have been known for many years/ the synthesis of the first divalent samarium bis(amidinate) required the use of a sterically hindered amidinate ligand, [HC(NDipp)2l (Dipp = C6H3Pr2-2,6)/ As illustrated in Scheme 54, the dark green compound Sm(DippForm)2(THF)2 (DippForm = [HC(NDipp)2] ) can be prepared by three different synthetic routes. Structural data indicated that hexacoordinated... 

Table 6 Structural data for [Bu2Sn(IV)] and [Et2Sn(IV)] carbohydrates and related compounds complexes, obtained by X-ray diffraction and... 

EXAFS data were analyzed by using multishell models up to 300 pm. These results are the first structural data (bond lengths) on complexes formed with organotin(lV)-DNA and related compounds.Some data are collected in Table 6. The proposed structures are similar to those depicted in Figure 6. 

Comparison of the Mossbauer I Agxp I values with those calculated on the basis of the pqs formalism revealed that the organotin(IV) moiety has Tbp geometry, and in certain cases geometry too. Some of the complexes contain the organotin(IV) cation in two different environments. Finally, the local structure of the maleic acid complex formed with [Bu2Sn(IV)l was determined by an EXAFS method.The structural data are collected in Table 6. Similar studies... 

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

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