Co(NH_3)_6^3+ has a maximum absorbance in the UV-Vis of 475 nm and appears yello

Question

Co(NH_3)_6^3+ has a maximum absorbance in the UV-Vis of 475 nm and appears yellow-orange. If we assume this is due to the crystal field splitting, what is Delta in J/molecule? Assuming that metals with a +2 charge attach two 2, 4-pentanedionate anions and two water complexes, write the balanced reaction for nickel(II) nitrate hexahydrate with 2, 4-pentanedionate anions to produce the assumed product. 3. If 0.148 g of the metal nitrate discussed in (2) above is added to the reaction beaker, a. what is the theoretical yield of product? (Show calculations) b. If we assume we have the anhydrous product (no waters), what is the theoretical yield? (Show calculations.) c. Which assumption would make your percent yield larger? 4. What color do you expect the crystalline copper(II) 2, 4-pentanedionate (anhydrous to be (you'll need to search)? List one use for the metal 2, 4-pentanedionates and the reference for both answers.

Explanation / Answer

1. Co[(NH3)6]3+ has a maximum absorbance at wavelength (l) = 475 nm = 475 x 10^-9 m

Using,

Energy (E) = hc/l

with,

h = planck's constant

c = speed of light

we get,

E = 6.626 x 10^-34 x 3 x 10^8/475 x 10^-9

   = 4.2 x 10^-19 J

So,

delta energy in J/molecule would be = 4.2 x 10^-19/6.023 x 10^23

                                                  = 6.95 x 10^-43 J/molecule

2. Balanced equation,

Ni(NO3)2.6H2O + 2 (CH3COCHCOCH3)^- ---> [Ni(CH3COCHCOCH3)2(OH2)2] + 4H2O

(CH3COCHCOCH3)^- = 2,4-pentanedionate anion

3. If we start with 0.148 g of metal nitrate,

a. theoretical yield of product = 0.148 x 292.9/290.79

                                                = 0.150 g

b. For anhydrous product, we get a trimer formed,

Theoretical yield of product = 0.148 x 770.1/290.79

                                             = 0.392 g

c. To get maximum percent yield, we assume that all of Ni2+ has reacted with pentandionate anion added.

4. the color of copper(II) 2,4-pentandionate (anhydrous) to be expected would be pale-blue (often white) in color. Co(acac)2 complex is used to catalyze michael addtions reactions, (Reference: E.J. Parish, S. Li, (2004). "Copper(I) Acetylacetonate". In Paquette, L. Encyclopedia of Reagents for Organic Synthesis. New York, NY: J. Wiley & Sons).

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