Microscopic Identification of the Crystals of Dimethylglyoxime Complexes of Cobalt (II), Iron (II), and Nickel (11) Sabitra S. Brush Wakulla High School, Route 2,Box 4800, Crawfordville, FL 32327 This experiment provides an interesting and visually stimulating study of the different colors and shapes of crystals of transition metal dimethylglyoxime (DMG) complexes. Furthermore, it enables the student to examine the crystals microscopically and to realize what shapes are characteristic of the various complexes. Experlment Apparatus Light microscope at a magnification of 90X; 12-in. Dewar flask. Preparation of Crystals of CdDMQdPyk and WDMG);IPY~Z~ Dissolve 3.6 g of dimerhylglyorime in 50.0 mL of pyridine. Caution: Pyridine is toxic hg inhalation. Ilre s hood. Also usegogales. apron, and gloves. The DM(; ianur very aoluhle in pyrrdine, socrush the particles with a glass rod and shake the mixture to encourage dissolution. Add 18.0 mL of 3 M HC1 and 50.0 mL of 95% ethanol. Shake vigorously and allow to stand for 30 min. This mixture, light pink in color, is reagent A. Pour 1 mI,of 1%Co(NO& into a small test tuhe, add 5 drops of reagent A, and shake the suspension. Place one drop of the dark yellowish-brown suspension on a microscope slide and examine it under the microscope. Blatk, X-shaped crystals of Co(DMG)z(Py)zwill be seen. Repeat the experiment using 1mL of 1%FeS04.The suspension with reagent A appears reddish in color, and the crystals are orange and comb shaped. Reagent A may he prepared 24 h in advance. (The flask must he stoppered and stored in a hood.) When 10 mL of reagent A was added to 40 mL of Co(NO& or FeSOi solution, a large amount of crystals was obtained. However, attempts to collect the crystals by filteringwere unsuccessful. To dispose of pyridine2add it to a mixture of 9 parts of sand to 1 part of sodium carbonate, place in a paper bag, and then inside a cardboard carton. Burn it in an open incinerator or open area. Preparation of Crystals of Nickel Dimethylglyoxlme T o 100 mL of 1%Ni(NO& add about 8 droos 6 M NHaOH until the solution is alkaline, then add 15 m i of lPo dimbrhvlalvoxime to ~recioitacethe brieht red nickel dimethvl&xime. ~ i l t e ;anddry in a desiccator. Heat 400 mL of venetahle oil to 150 "C. Place 10 mL of N.N-dimethylform&ide (DMF) in a test tuhe and heat. Caution: DMF h a s a n extremely irritating vapor. Absorption through t h e skin may be harmful. u s e it in a hood. If liquid gets in the eyes, flush immediately with plentv of water. Add small amounts of the nickel DMG nrecioit k e to the hot DMF and continue heating until it di&olv\s. When no more nickel DMG will dissolve, add a s m d l amount
of the DMF and continue heating until a clear yellowish solution is obtained. Pour 1mL of the solution into a test tuhe and set aside to cool. Place the heated oil in the Dewar flask, and suspend in i t the test tube containing the rest of the saturated solution. Stopper the flask, and do not disturb for a t least 48 h. The hot oil bath ensures that the saturated solution will cool a t a slower rate, and this tends to produce larger crystals. Place a drop of the 1mL of cooled solution, on a microscope slide and examine under the microscope. The red, needle-shaped crystals of the complex, nickel DMG, can be observed easily. When the crystals of nickel DMG are produced by very slow cooling, they appear larger, very shiny, and dark brown in color. Collect them by filtration and store in a closed labelled container. Under the microscope notice the characteristic needle-like appearance. Place some of these crystals on apiece of filter paper and crush them to observe adistinct bright cherry red color. Despite its solubility in water, the complex has some solubility in organic solvents such as chloroform and DMF, which permits two interesting observations: (1) the yellow color (and electronic spectra) of molecular N~(DMG)zin solution and (2) the shape of individual crystals, since crystallization from hot DMF results in long needle-like crystals. The fact that the crystals immediately flash the familiar characteristic cherry red color when crushed is an example of dichroism in crystals. To dispose of dimethylglyoxime2 add a layer of sodium bisulfate, spray with water, and neutralize with 6 M HCI. When i t is neutral flush down the drain with large quantities of water. T o dispose of DMF3 hydrolyze i t by refluxingfor 5 h in 250 mL of 36% HCI per mole of DMF. I t can then be washed down the drain. Acknowledgment This experiment was done as part of CH 5455C at the Chemistry Department of Florida State University. I would like to thank my lecturer E d Mellon. I am also grateful to Virgil Goedken for his assistance in the preparation of the nickel DMG crystals.
' Pino. F.; De Pablos. F.; Gomez Ariza, J. L. Microchem. J. 1984,
30. 1.
Flinn ScientificInc. The Science Instructor's Safer Source; Batavia. IL. 1986: DD 285-286. "Prudent Gctices for Disposal of Chemicals from Laboratories; National Academy Press: Washington, DC. 1983; p 68.
Volume 65 Number 1 January 1988
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