Two-coordinate Compounds

1 Two-coordinate Compounds. - X-Ray diffraction studies, together with quantum-chemical calculations, have been used to explain peculiarities in the molecular and electronic structures of halogen-substituted phosphaalkenes.  

XRD analysis of l,l,l,3,3,3-hexafluoro-2-propanyloxy-(2,4,6-tri-t-butylphenyl-imino)phosphine (57) revealed a P=N bond-length of 1.526 A, the shortest ever observed in trans (E)-iminophosphines. X-Ray structural analysis of the diphosphene DmpP=PDmp,where Dmp = 2,6-dimesitylphenyl-, also revealed a trans configuration (about P=P) and a short P=P bond-length of 1.985 The 

X-ray crystal structure of the novel organoantimony cage compound C4BuSP4Sb2 (58) displayed weak intermolecular interactions.  

---

The chemistry of mercury(II) is dominated by the stability of two-coordinated compounds but in silylmercury compounds three- and four-coordinated anions, [(R3Si)3Hg] and [(R3Si)4Hg] are formed. 

J Phosphorus-31 NMR. - Positive chemical shifts, 63 ip, are downheld of the external reference 85% phosphoric acid, and are usually given without the appellation ppm. One-coordinate compounds studied include phosphaalkynes and their cyclotetramerisation. Two-coordinate compounds. The NMR data of the simple phosphaalkenes R CH=PR (R/R = H/H, H/Me, H/Et, Me/H, Me/ Me, Ph/H, and Ph/Me) have been reported for the first time, with 6 in the range + 179 to +285, and found to be consistent with the proposed structures. Stereochemistry of the (Z)- and (E)-isomers was established according to the cis-rule. The P and NMR data of a series of 40 iminophosphines, R-P=N-R, revealed that their E/Z stereochemistry can be predicted on the basis of a simultaneous comparison of the values of 831 p and Jpn- ... 

A number of these have been mentioned above. The Hg2+ ion has indeed a strong tendency to complex formation, and the characteristic coordination numbers and stereochemical arrangements are two-coordinate, linear, and four-coordinate, tetrahedral. Octahedral coordination is less common a few three- and five-coordinate complexes are also known. There appears to be considerable covalent character in the mercury—ligand bonds, especially in the two-coordinate compounds. The most stable complexes are those with C, N, P and S as ligand atoms. 

Hg(S-w-Bu)2 (178). Structural trends are difficult to rationalize for this series since the sterically smaller ligands EtS" and MeS form neutral, linear, mononuclear two-coordinate compounds (24, 25). 

The isotropic shifts of the three-coordinate [Hg(SR)3] anions agree quite well with the solution chemical shifts, indicating the lack of multiple species in solution (Table XIII). The isotropic chemical shifts of the three-coordinate species are deshielded from the two-coordinate compounds by... 

Analyze We are given the chemical formulas for two coordination compounds and assigned the task of... 

Solution. The two formation constants are simply multiplied together fi2 = K,K2 = IJx 10. The reason why K2>K in this case has to do with the different geometries of the two coordination compounds. The actual stepwise chemical equations are as follows ... 

When Co(ll) is dissolved in aqueous solution, it makes the extremely pale pink-colored complex [Co(hl20)j]. When concentrated HCI is added to the same ion, it forms the intensely blue-colored complex [CoCy . Explain the relative colors and intensities of the two coordination compounds. 

An electron transfer (ET) reaction is defined here as an oxidation-reduction reaction that occurs between two coordination compounds. The compounds may be the same species, but where the metals have different oxidation states (a selfexchan reaction), or are completely different species (a cross-reaction). An example of a self-exchange reaction is given in Equation (17.41), where Co is an isotopically labeled cobalt a cross-reaction is given by Equation (17.42). 

The reactants first have to be brought to reaction distance, as shown in Figure I7.I0 this requires a work term associated with the lost translational and rotational free ener gy involved in bringing the two reactants together. It also involves a change in the electrostatics as the distance between the two species moves from infinity to the reaction distance. This first term is given the abbreviation AG ( in Equation (17.43). Once the two coordination compounds are at reaction distance, there is still an activation barrier associated with the formation of the precursor complex, as shown in Figure I7.I0. This barrier involves both inner-sphere (AG ) and outer-sphere (AG-g) components. 

The oitiy two-coordinate compounds are the volatile two-coordinate bent Ln° alkyls [Ln(C(SiMe3)3)2] (Ln = Yb, Eu). These contain just two Ln-C a bonds, but are bent... 

Two coordination compounds which differ in the distribution of ions between those directly coordinated and counterions present in the crystal structure are called ionization isomers ... 

Fig. 2.41 Molecular structure of Bis(tris(trimethylsilyl) methyl)Fe , a rigorously linear two-coordinate compound of Fe in HS state with ideal staggered Dsd symmetry [75]. Fe Mossbauer spectmm of Bis(tris(trimethylsilyl) methyl)Fe , recorded at 4.2 K in zero applied magnetic field [74]. The internal magnetic field derived from the distance between the two outermost resonance lines, S1-S2, is 152 T, the largest field ever observed in an iron compound...

Figure 1. Chemical shift ranges for various coordination numbers. Shifts in ppm relative to 85 % H3PO4 as zero. Solid bars indicate the most usual ranges and the lighter lines the limits of known values. NOTE Subsequent to the preparation of these Figures, the shift range for two-coordinate compounds has been extended to +1362 ppm (see page...

The two coordination compounds whose formulas are shown here have the same central ion (Cr " "), and five of fhe six ligands (NH3 molecules) are the same. The compounds differ in fhaf one has S04 ion as fhe sixfh ligand, wifh a CP ion fo neutralize the charge of fhe complex ion, whereas fhe other has CP as the sixth ligand and S04 to neutralize the charge of fhe complex ion. 

---