Bidentate nitrates

Mn(N03)4] , [Fe(N03)4] and [Sn(N03)4], which feature dodecahedral coordination about the metal [Ce(N03)5] in which the 5 bidentate nitrate groups define a trigonal bipyramid leading to tenfold coordination of cerium (Fig. 11.17b) [Ce(N03)6] and [Th(N03)6] , which feature nearly regular icosahedral (p. 141) coordination of the metal by 12 O atoms and many lanthanide and uranyl [U02] complexes. It seems, therefore, that the size of the metal centre is not necessarily a dominant factor. 

Figure 11.19 Schematic diagram of the centrosymmetric dimer in [Cii2(NO ).i(py) lpy showing the two bridging nitrato groups each coordinated to the 2 Cii atoms by a single O atom the dimer also has an unsymmetrical bidentate nitrate group on each Cu.

The anhydrous nitrates can be prepared by the action of N2O5 on MCI4. Ti(N03)4 is a white sublimable and highly reactive compound (mp 58°C) in which the bidentate nitrate ions are disposed tetrahedrally around the titanium which thereby attains a coordination number of 8 (Fig. 21.4). Infrared evidence suggests that Zr(N03)4 is isostmctural but hafnium nitrate... 

The distortion arises because the bidentate nitrate ions are coordinated asymmetrically to such an extent that the stereochemistry may alternatively be regarded as approaching tetrahedral (p. 1217). 

Figure 30.5 Nitrato complexes of Ce". (a) [CefNOa) ] " the Ce" is surroundecl by 12 oxygen atoms from 6 bidentate nitrate ions in the form of an icosahedron (in each case the third oxygen is omitted for clarity). Note that this implies an octahedral disposition of the 6 nitrogen atoms, (b) [Ce(N03)4(0PPh3)2].

Red moisture-sensitive crystals of K2Ir(N03)6, isomorphous with the Pt analogue and believed to contain 12-coordinate iridium, with bidentate nitrates are made by ... 

Figure 5. IR spectra of s.o. samples after various treatments. Section a after adsorption of NH3 (1 mbar) at RT Zr02 (curve 1), ZV0.58(a)pH4 (curve 2), ZV1.21(a)pH4 (curve 3). Section b ZV0.58(a)pH4 sample after adsorption of NO+O2 at 623 K (curve 1), after subsequent adsorption of NH3 (1 mbar) at RT (curve 2) and after subsequent heating at 623 K (curve 3). Bands assigned to bridged bidentate nitrates ( ) and to chelating nitrates ( ). Section c the same treatments as in section b on s.o. 1.21(a)pH4.

For the abatement of NO with NH3 in the absence of O2, ZV catalysts give low, but stable activity. The activity is strongly enhanced in the presence of O2- This is a common feature to all SCR catalysts, including the ZSM-5 based system [30]. In the presence of O2. our results show the formation of bidentate nitrates and, on NH3 addition, their transformation into chelating nitrates. Our results also show that the... 

Figure 10.6. In situ Fourier transform infrared spectra of decane SCR-NO in the presence and absence of hydrogen on Ag/Al203 at 200°C. Evolution of intensities of the bands characteristic for adsorbed species (monodentate nitrates 1245 cm-1, bidentate nitrates 1295 cm-1, —CN 2150 cm-1 and —NCO 2230 cm-1. 1000 ppm NO, 6vol.%02,750 ppm decane, Oor 1000 ppm H2 (reproduced with permission from Ref. [12]).

Although the bulk of work with NOz as a ligand features Co111, nitrite can also be O- or N-bonded to Co11, and both modes have been observed in complexes formed by the reaction of several PR3 compounds with Co(N03)2, as well as in mixed nitro/nitroso complexes.375 The product Co(NO)(N02)(PEt3)2 reacts with dioxygen to form Co(N03)2 (OPEt3)2, a distorted octahedral structure with bidentate nitrate and cis phosphine oxides (102). 

Bi-0 2.54(l)-2.68(2) A], In contrast, the nine-coordinate capped square antiprism geometry for bismuth in [Bi(N03)3(H20)3] (18-crown-6) does not involve the expected multidentate ether coordination to bismuth, but rather a hydrogen-bonded interaction of the crown ether with the hydrated bismuth center chelated by bidentate nitrate groups [Bi-0 2.38(2)—2.56(2) A] 32, implying that the hexado-... 

The L M in the complexes of lanthanide nitrates with TMSO decreases along the lanthanide series (264, 265). All these complexes contain both bidentate and mono-dentate nitrate groups (264), the monodentate nitrates giving way to bidentate nitrates as the cationic radius decreases. 

In all other complexes of lanthanide nitrates, the mode of coordination has been identified, with some ambiguity, from IR data alone. In most of the cases, either the criterion suggested by Addison et al. (287), Curtis and Curtis (288) or Lever et al. (289) has been used for this purpose. Ionic nitrate groups have been identified in the complexes of BuL (60), HMPA (223), and O-PhenNO (178) with lanthanide nitrates. Both unidentate and bidentate nitrate groups are present in the complexes of lanthanide nitrates with MP (232), OMPA (234), CMP (240), TMSO (264), DMF (42), and BuL (60). Complexes of PyO, 2-MePyO, 2,6-DMePyO, and 2,4,6-TMePyO which have the general formula Ln(L)3(N03)3 -x H20 contain only bidentate nitrate groups (152,170). 

The vibrations of the anions are also affected by the change in the strength of interaction between the anion and the metal ion. For example, in the complexes of TPP with lanthanide nitrates (201), the band around 1300 cm-1, assigned to of the bidentate nitrate group (C2v), increases in frequency from 1282 cm-1 for the bis-... 

Ten coordination has also been observed in Pr(H20)6(N03)3 (382). The Pr(III) ion is surrounded by three bidentate nitrate groups and four water molecules in a bi-capped dodecahedral fashion. The average Pr—0(H20) distance (2.47 A) is slightly shorter than the four Pr—O(nitrate) distances (2.73 A). The Pr—0 distances for the third nitrate group are significantly shorter than the rest ( 2.48 A). 

Several cubic double nitrates of the composition K3M2(N03)9 (M=Pr, Nd, Sm) have been prepared by Carnall et al. (228), to study the electronic and vibrational spectra of the complexes. During this study, they have also investigated the structure of the Pr(IH) analogue and found that each Pr(III) ion is surrounded by twelve oxygens, from six bidentate nitrate groups, in a distorted icosahedral... 

The nitrate ions in K3M2(N03)9 form two nonequivalent sets, each with distinct bonding characteristics to Pr(III) and K. Infrared and Raman Studies confirm the strong bonding characteristics of the bidentate nitrates with the lanthanide ions. 

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