Coordinated nitrate

Coin-cyclam322-324 and Nin-cyclam322 catalyze the electroreduction of nitrate in aqueous electrolytes with good current efficiencies and turnover numbers, giving mixtures of ammonia, nitrite, and hydroxylamine at a variety of electrode materials. Mechanistic investigations suggested the adsorption of electroreduced Co1- and Ni1 cyclam onto the electrode surface,322 and the formation of an oxo-metal bond via reduction of coordinated nitrate.323... 

In fact, it is both surprising and gratifying to find so much similarity and correlation between Craq002+ and, say, HbOo or MbOo in reactions with common substrates, such as NO. In all the cases, a short-lived peroxynitrato intermediate forms with similar kinetics, and ultimately produces free N03 in a scheme that involves smaller or greater amounts of free N02 and LMIV0 (169,182,186,201,230) and coordinated nitrate. The reactivity of LMIV0 toward NO and NO2 in subsequent reactions is again not too different for LM=Craq... 

The unsymmetrical derivative, L2, in which one benzimidazole group is replaced by a 2-pyridyl moiety, and its complexes with europium and terbium have been further studied for their photophysical properties (37). The coordinated nitrate anions in the [ ( 2)( ) ]... 

Use of silver nitrate and only a small excess of trimethyl phosphite also gave rise to an exothermic reaction in this case AgL2N03 was isolated.193 The low conductivity of this complex in acetone and its IR spectrum in the nitrate region suggested the presence of coordinated nitrate. In acetone, it was found to be monomeric and only poorly conducting. The structure was expected to contain a bidentate nitrate. In acetonitrile, dissociation was evident due to the 10-fold increase in molar conductivity. 

Figure 12. Solvation of the Srcl8C6(N(> )2 complex with coordinated nitrates in dry versus "humid" [BMI][PF6] solution. Left typical snapshots at the end of the dynamics. Right RDFs Sr BMI (bold), Sr P (plain) Sr F (dotted) and Sr OH2 (inversed ordinate).

Bm at 299 K 2.22 BM at 87 K). Cyclic voltammetry data of 26 in DMF consisted of two quasireversible peaks separated by 550 mV. The fact that conductivity measurements reveal that 26 is a 2 1 electrolyte in MeOH suggests a coordinated nitrate ion. 

Ionic nitrate D3h has 4 vibrations (3 IR active 1 Raman active), coordinated nitrate C2V has 6 IR active, and 6 Raman active vibrations. The doubly degenerate V4 band of ionic nitrate (700 cm-1) is split into V3 and V4 upon coordination. Further Raman polarization studies can distinguish between monodentate from bidentate nitrate and bridging nitrate groups. As an example La(HMPA)3(N03)3 has both ionic and coordinated nitrate [161]. 

Complexes with 2,7-dimethyl-1,8-naphthyridine of the formula [233] Ln(2,7-dmnapy)2(N03)3 have been identified containing coordinated nitrate groups C2V symmetry. A coordination number ten for these complexes seems plausible. The IR data for ionic and coordinated nitrate groups are given below. 

With ethylenediamine complexes of the formula Ln(en)3X3 and Ln(en)4X3, where X = C1 , Br , NO, CIOJ have been characterized. IR data indicate that the tris and tetrakis complexes of the fighter lanthanides La-Sm, contain both ionic and coordinated nitrate groups. By contrast tetrakis complexes of heavier lanthanides, Eu-Yb contain ionic nitrate. This is possibly due to steric factors resulting from decreasing cationic radius that force the nitrate out of the coordination sphere of the lanthanides. A coordination number of 8 for tris complexes and a number of 9 for fighter lanthanide tetrakis complexes appears reasonable [234]. The thermodynamic parameters obtained show enthalpy stabilization for... 

The nitrate complexes Tb(N03)3(bipy)2, Ln(bipy)2(N03)3-H20 (Ln = Dy, Ho) have been synthesized and characterized. The anhydrous complexes have coordinated nitrate groups suggesting a coordination number of ten for Ln(bipy)2(N03)3. The molecular geometry is that of a bicapped triangularly faced dodecahedron [237] of D2 symmetry with Ln-O bond length of 2.605 A and two Ln-N bond lengths of 2.665 and 2.648 A. 

Complexes of the type Ln(phen)3Cl3 and Ln(phen)3Cl3 H2O with bidentate phenanthro-line and lighter lanthanides forming the hydrated complex have been reported [240]. With nitrate complexes of the type Ln(phen)2(N03)3 containing C2V, coordinated nitrate groups amounting to a coordination number 10 have been reported [238],... 

The synthesis of lanthanide complexes [244] with multidentate diethylenetriamine (dien) gave rise to two types of complexes, Ln(dien)3(N03>3 for Ln = La-Gd, and Ln(dien)2(N03)3 for Ln = La-Yb. The tris complexes contain ionic nitrate while the bis complexes contain both ionic and coordinated nitrate ions. The coordination number is nine in the tris complexes while it is not known with certainty in the bis complexes. With triethylene triamine (tren) two types of complexes [Ln(tren)(N03)3] and Ln(tren)2(N03)3 have been isolated. In the bis complexes both ionic and coordinated nitrate groups are present for larger lanthanides (La-Nd) but only ionic nitrate for smaller lanthanides (Sm-Yb). When perchlorate is the anion [245] Ln(tren)(C104)3 (Ln = Pr, Gd, Er) and Ln(tren)2(C104)3 for Ln = La, Pr, Nd, Gd, Er complexes were obtained. The monocomplexes contain coordinated perchlorate ions while the bis complexes contain ionic perchlorate ions. 

A number of complexes of 1,2-diamiuoethaue have beeu made. Infrared evidence for the complexes Ln(en)4(N03)3 indicated the presence of coordinated nitrate for the earher metals, so that the complexes were formulated [Ln(en)4(N03)](N03)2 (La-Sm) aud [Lu(eu)4](N03)3 (Eu Lu). Other complexes isolated iuclude perchlorates [Lu(en)4](C104)3 (Lu = La-Nd), chlorides, Lu(eu)4Cl3, [La(en)4Cl] lu2Te4 aud [Y(en)4](SH)2.72lo.28, tbe latter two having nine- and eight- coordination respectively. 

This report also describes two new examples of nitrato-metallate coordination compounds which involve a phosphorus-containing ligand. One is the complex [AgL2N03] and the other the blue diamagnetic cobalt(I) complex anion [CoL(N03)2] Of the more than 100 compounds reported in the literature, which are suspected to contain coordinated nitrate, the 12 examined by x-ray diffraction technics are listed in Table II. Two reviews on metal-nitrate interactions have appeared recently (3, 19), so only some general observations will be made here. 

Thus, ascribing infrared bands to monodentate nitrates on the assumption that the metal atom adopts its usual coordination number is somewhat tenuous in the present absence of clear-cut examples of monodentate nitrate structures. Despite the fact that about 30% of the coordinated-nitrate compounds in the literature are suspected from infrared studies to contain monodentate nitrate, a significant portion may on structural analysis be found to possess bidentate nitrate if the ratio of structures in Table II is at all representative. 

Table III. Infrared and Raman Modes for Free and Coordinated Nitrate...

Montmorillonite, a bentonite sample finm Linden/Bavaria, was used for the introduction of the binuclear complexes by cation exchange as previously reported [7]. The complexes can be removed fi om the interlayers only by highly concentrated solutions of NaC104 or KCIO4. As inferred fi om TGA when the clay sample is heated in an Ar/02 atmosphere, the Fe coordinated nitrate is removed between 160 and 260°C and the ligand is cracked between 350 and 450°C. 

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