Thiocyanate Complexes of Osmium

University of the Pacific Scholarly Commons University of the Pacific Theses and Dissertations Graduate School 1953 Thiocyanate complexes of osmium Craig Albert Townsend Jr. University of the Pacific Follow this and additional works at: https://scholarlycommons.pacific.edu/uop_etds Part of the Chemistry Commons Recommended Citation Townsend, Craig Albert Jr.. (1953). Thiocyanate complexes of osmium. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/343 This Thesis is brought to you for free and open access by the Graduate School at Scholarly Commons. It has been accepted for inclusion in University of the Pacific Theses and Dissertations by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. THIOCYANATE COHPLEXES OF OSJYliUJ:vi A Thesis presented to The Faculty of the Department of Chemistry College of the Pacific In Partial Fulfillment pf the Requirements for the Degree }'laster of Arts ,by ,Craig Albert Townsend Jr. "I ,A_ugust 1953 ·ACKN 0\rJLEDGEiviENT The writer is indebted to the members of the staff for completion of this work, especially to Dr. Emerson Cobb for his encouragement and to Dr. Don DeVault for assistance in the mathematical computations involved in the solution of the problem. TABLE OF CON 'l'EN 'l'S PAGE Properties and Uses of Osmium. • • • • • . • • . • 1 Spectrophotometric Methods • • • • • • • • 5 11 Experimental Observations • . 23 Discussion of Results • • • . LIST OF TABLES TABLE PAGE I. Optical Densities of Thiocyanate and Osmium Nixtures before the Attain- ment of Equilibrium • • • • • • • • 16 II. Optical Densities of Thiocyanate and Osmium Mixtures after the Attain- ment of Equilibrium • . 17 III. Values for the Dissociation Constant by the Hethod of Frank and Ostwald •• • • 18 IV. Optical Densities of Diluted Solutions of the Complex • • • • • • . • . • 18 •' I' LIST OF FIGURES FIGURE PAGE 1. The Absorption Spectrum of 20 Osmium Thiocyanate • • . • • • • 21 2. Plot of Log D Against Log (CNS-) 22 Plot of ab Against a + b • • • • • • • • 3· n I PROPERTIES AND USES OF OSMIUM Osmium is a hard grey brittle metal which scratches glass. It has a melting point of 2700°C, and a specific gravity of 22.4, which is greater than any other known substance. The grey color of osmium resembles the grey color of iron and rutheniu.m. Osmium was discovered in 1803 by Tennant in the insoluble residue remaining Rfter treating an alloy of the platinum metals with acid. Osmium occurs in nature alloyed with the other metals of the platinum group. One type of alloy includes all six of the platinum metals, osmium, irid.ima, platinum, ruthenium, rhodium and palladhiirl. Osmium also occurs in an alloy of osmium and iridium called osm:i.r5.dium. These alloys are usually recovered by placer mining methods. Canada, Russia, Colombia, South Africa and the United States are the worlds producers of platinum metals. The beds of Alaskan rivers contain platinum metals. Osmium has limited uses due in part to scarcity. Its cost is approximately fifty dollars per ounce. Haber found that osmium metal catalizes the synthesis of a.mmonia from the elements. Other investigators have ranked osmium first in catalytic powers among the platinum metals. Osmium alloys are used for bearings in place of jewels in precision instruments because of their resistance to wear. Osmium alloys are also used in pen points because of their resistance 2 to wear and corrosion. Osmium tetroxide finds use as a catalyst in inorganic and orgenic reactions. It is employ ed as a catalyst in the quantitative determination of arsenic in which arsenite is titrated with eerie sulfate. Osmium tetroxide catalizes the action of potassium permangan ate on maleic acid to form meso-tartaric acid; and also catalizes the addition of hydrogen peroxide to other ethelen ic compounds to form glycols. Osmium tetroxide is used to develop fresh finger prints. It also finds use as a harden ing and staining agent in making sections for study under the microscope in biological work. Osmium, the fj.rst of the third triad, atomic number 76, atomic weight 190.2, is noble like the other metals of the platinum group. It is attacked by hot nitric acid or by oxygen when heated in the air to form the tetroxide, and can be reduced to the metallic state by most other metals. Osmium and ruthenium have a greater tendency to form complexes than iron. Osmium and ruthenium form tetrox ides, but iron does not. Salts of the +2 state of osmium are unstable in aqueous solution. The Osi2 salt can be prepared from solution but lt is insoluble. In the +3 state we find stable salts of the K3 0sCl6 (potassium chlorosmi te) type. In the +1~ state K2 0sCl 6 (potassium chlorosmate) and K2 0s04 (potassimn osmate) are two exruaples. In the +6 state osmyl ions such 3 = as Os02 Cl 4 are formed. These are unstable in acid solution. In the +8 state osmium tetroxide is the most import ant compound. Osmium tetroxide, melting point 40°C. boil- j_ng point 13)°C., is appreciably volatile at room temperatures. It is much more soluble in organic solvents than in water. This suggests that the bonds in osmium tetroxide are of the coordinate covalent type. The disagreeable odor of the tetroxide, which is poisonous, may have given the element . its name. Osmium means 11 smell 11 in Greek. Bven solutions of Os0 4 as dilute as 10-5M have a disagreeable odor of Os0 4 • At l)°C. the tetroxide has a solubility of ).88 parts per hundred. Solutions of Os0 4 are faintly acidic: K for 1 H2 0s06 is 8 x lo- 3. It is a good oxidizing agent in acid solution being about as strong as bromine. OsF 8 , formed by direct combination of osmium and flourine, hydrolizes to Os04 in aqueous solution. The cornplexing nature of osmium is shown by the number of complexes of osmium which have been found. Ogburn (1926) discovered the following colored complexes. Rea@nt Color formed NH 4 OH N a 2 S2 03 Orange Hydrazine Sulfate Green Hg (CN) 2 Violet KCNS Hose (Upon boiling) Na2S2 0 3 Red Sn Cl2 Yellow Anthranilic acid Violet Brucine Yellow Analine Sulfate Violet Toluidine Green changing to rose 4 Reagent Color formed Pyrogallol Blue green B-napthylammine Blue Pyrocatechol Blue green Resorcinol Green Benzophenone Violet Allyl-thiorea Rose changing to violet 11hiourea Hose Diphenylthiocarbazid.e Green Thiocarbanilide Rose Some of the chemical properties of osmium are similar to chemical properties of iron and ruthenj_um. A comparison of their atomic structures shows similarity. Atomic structure Atomic Number of Electrons in Each ~uantive Group Number Element 18 28 2P 3S 3P 3d 4S 4P 4d 4f SS SP Sd. Sf 6s 26 Fe 2 2 6 2 6 6 2 44 Ru 2 2 6 2 6 10 2 6 7 1 76 Os 2 2 6 2 6 10 2 6 10 14 .2 6 6 2 ':Phe similarity appears to be greater between osmium and iron than between ruthenium and iron. SPECTROPHOTOMETRIC METHODS The thiocyanate complexes of ferric iron have been quite thoroughly investigated; and a recent piece of work has been done on the thiocyanate complex of ruthenium (Yaffe and Voigt, 1951). These investigations establish the formula Fe(CNS)++ for the iron complex and the formula Ru ('CNS)++ for the ruthenium complex. The dissociation constants for the two complexes were determined in these investigations. As a result of a seminar report on the work of Yaffe and Voigt given in the suruner of 1952 at the College of the Pacific, the problem of this research was suggested by Dr. Emerson Cobb. In order to solve the problem, a study was made of the work of earlier investigators of the ferric iron thiocyanate complex. Valkenburg and Schesinger gave Fe ( CNS )~ for the formula. This was determined by obtaining the molecular weight from the loHering of the freezing point of ether and benzene solutions of the complex. The presently accepted formula was determined in 191-!1 by Bent and French by use of a spectrophotometer. Optical densities were determined for varying concentrations of thiocyanate, holding the concentration of iron constant; and for varying concentrations of iron, holding the concentration of thiocyanate constant. Then if K = log Pem (CNS )n = m log (Fe) n log ('CNS) - log K 6 If (Fe+++) is constant, plotting log (:Cl'JS-) against log D for log Fern ( 'CNS) gives a line with a slope of n and if (CNS-) is constant, plotting log (Fe+++) against log D gives a line with a slope of m. Both m and n were found to be 1, showing the formula must be Fe (·eNS)++: log (Fe ) log D log D Employing the method of least squares K was found to be 3o3xlo-2 • In the same year another determination was made by Edmonds and Birnbaum with a few refinements. Fe(Cl04 ) 3 1rJas used instead of Fe Cl3 • Again one component was held constant while the other was varied; and K was determined from measure- ments of the percent transmittance. (F If K = ~bm = ~bm , wh er·e a == 'e +++ ) , b = c~ c 2 c = (FeCl..TS++), and By the Beer·-Lambert law c = Der making K = ( P..2. ~ ) (lb.._b...a&) el el e -~&-..--,-( ,--b-2~:0-l. --:--..,..!2..J..::~D~-.)- el el el 7 Using this equation, K was found to be 7.9 x 10-3and n to be 1. · In 1942, Gould and Vosburgh determined the formula of the complex by the method of continuous variations. 1-x +++ parts of 0. 02 M Fe +x parts of 0. 02 M CNS ~ were mixed and the optical densities were read.

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