Preparation and Reactions of Coordination Compounds: Oxalate Complexes To gain some familiarity with coordination compounds by preparing a representative compound and witnessing some typical reactions. Apparatus balance Bunsen burner and hose 8-oz wide-mouth bottle No. 6 two-hole rubber stopper glass stirring rod 9-cm filter paper wire gauze vial Chemicals cis- and trans-K[Cr(C 204h(H20h] (prep given) 6MNH3 KzC204 · H20 (potassium oxalate monohydrate) acetone ferrous ammonium sulfate 6MH2S04 ice

9-cm Buchner funnel 250-mL suction flask aspirator 100-mL and 250-mL beakers thermometer ring stand and iron ring glass wool

Experiment

OBJECTIVE

APPARATUS AND CHEMICALS

aluminum powder 6MKOH H2C204 (oxalic acid) KzCr207 (potassium dichromate) 50% ethanol 95% ethanol absolute alcohol CuS04 · 5(H20) 6%H202 6MHC1

When gaseous boron trifluoride, BF3, is passed into liquid trimethylamine, (CH 3)3N, a highly exothermic reaction occurs, and a creamy white solid, (CH 3)3N: BF3, separates. This solid, which is an adduct of trimethylamine and boron trifluoride, is a coordination compound. It contains a coordinate covalent, or dative, bond uniting the Lewis acid BF3 with the Lewis base trimethylamine. Numerous coordination compounds are known, and in fact nearly all compounds of the transition elements are coordination compounds wherein the metal is a Lewis acid and the atoms or molecules joined to the metal are Lewis bases. These Lewis bases are called ligands, and the coordination compounds are usually denoted by square brackets when their formulas are written. The metal and the ligands bound to it constitute what is termed the coordination sphere. In writing chemical formulas for coordination compounds, we use square brackets to set off the coordination sphere from other parts of the compound. For example, the salt NiC1 2 · 6H 20 is in From Laboratory Experiments, Tenth Edition, John H. Nelson and Kenneth C. Kemp. Copyright © 2006 by Pearson Education, Inc. Published by Prentice Hall, Inc. All rights reserved.

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DISCUSSION

Preparation and Reactions of Coordination Compounds: Oxalate Complexes 2+

30

II

/c..'c=o

0 I "c-0~1,, I ~P I '·co···'" ..