THE PREPARATION OF NICKEL (II) TITIOCYANATE COMPLEX COMPOUNDS WITH CERTAIN ORGANIC BASES AND THE DETERMINATION OF THEIR HEATS OF FORMATION by DON WAYNE CARLE A THESIS Subiitted to OREGON STATE COLLEGE in partial fulfillment of the requirements for the deroe of MASTER O? SCIENCE Juno 152 AP PH 0VLD : Associate Professor of Chemistry In Charge of ?ajor Head of Chemistry Departtnent Chairman of School Graduate Coiittee Dean of Graduate School Date thesis is presented October 31, 1951 Typed by N. Bush. A CKNOWLEDGELIENT The writer wishes to express his grat- itudo to Dr. A. V. Loan for his continued encouragement end assistance during the course of this study0 The writer also sincerely appreciates the many helpful suggestions made by Mr. D. C. flush, Mr. C. J. flogers and Dr0 E. C. Gilbert. TABI OF CONTENTS Title PaLL:e i INTRODUCTION. PREPARATION OF THE COMPOTJDS . 5 ickoi 2hiocanate and o(-Picoi:Lne . , 6 ia1:oi Thiocyanate and .3Picoiine . ickoi Thiocyanato and -ficoiiiie . s a a a 13 Nickel Thiocyanate and Piperdine. a a a a a 14 Nickel Thiocyanate and Isoquinoline . 15 i.eke1 Thioc'ranate anu Quino1ine. a a a a 16 Preparation of ìcke1 Thiocranate . Lb PTTI'iTPflT f a a a a a a a a a a a a a TI-IL CALOflIMTLR. a a a a a a a a a a a a a a 20 heat Capacity of the Calorimeter. a a a a 21 Tst'Amc: r; cr1yTrnTrvkr .L_1fl..J %lZ s a a a . a i a a a a a a a t' A ( fv'1 -1 tfl m rn:r J.. a s a a s S a a q a e a a s s COMPARISON OF JATS OF FOR?ATION i s a a a s a a e s 40 SUMMARY, a a s a a a a s s a s e e a a e a s a a a 42 BIBLIOGRAPHY i a s a e a a a a a a e a . e e a e a TABLES Table Paco I Anal'yi of the Compounds. e . 10 lI Heat Capacity of the Calorimeter . 25 111 Heat of Eolution of i(CAS)2 e e e . e e 29 IV heat of o1ution of 3-Plcolino, . 30 V Heat oL o1ution of '-Picoline. VI Heat of solution of N1(CNE)2'4a-Picoline. 32 VII heat or Eolut1on of Ni(CNS)2'4 Y-Picolino. 33 VIII Heats of Formation . a . 34 FIGURES F1ure Pase t) T T 4.. Ç ,4.. .. 1ea.er . e e . e e e s e ±1 Heat Capacity of the Ca1oriieter . 26 III Heat of Solution of Ni(ONS)2 . Iv Heat of Solution of -?icoline. 36 V Heat of Solution of '-Picoline. VI Heat of Solution of i(ciS)24-kicolino. VII Peat of Solution of Ni(CNS)24 -Pico1ine. 39 TIlE PREPARATION OF NICKEL (II) THIOCYANATE COMPLEX COMPOUNDS WITH OERTAIN ORGANIC BASES AND TIlE DETERMINATION Oi THEIR HEATS OF FORMATION INTR ODU CT I ON The relative strength of metal-nitroon coordinate bonds in amine complex salts has been a subject of consid- erable interest to numerous investigators. Liost prior studios have considered relative bond strengths usin; a series or transition metals, or a series of dirferent acid radicals with the same metal, the arrime being either amron1a or more frequently pyridine. Davis (2,5,4,5,6), Lor;an (3,4, 5,6,9) arid others have :LnvestiCated a number of motal-pyri- dine complex salts. The purpose of this investiaton has been to select one sait, i.e., nickel thiocyanate, and to study the changes in bond strength using different amines, and thus to throw sorno light on the role of the amine in the coordinate bond. The amines origna1ly selected for this study vero the threo picolines, pipordine, Isoquinoline and quinoilne. The first four of these oranic bases represent a logical extension of the previous work with pyridine. ior reasons to be iven later, the actual experimental work largely has been reduced to the complex compounds of the picolines. 2 There aro three experimental techniques that have boon applied to cain insi;ht concerning bond strengtha with various pyridinated. salts. Those are the corriparison or dissociation pressures, volume chances durir formation arid heat$ of formation. Low d:L2ociation pressures have been shown to be ari indication of a relatively strong co- ordInate bond. The greater the volume 8hrinkage, i.e., the increase in density, the stronger the coordinato bond. The third comparative method, beets of forration, has not yet been applied to a large number of compounds. However, Bush (1) has determined the heats of formation or the tetra- pyridinated nickel thiocyanato and the hexapyridinated nickel cyanate. This work offered no comparative results since the coordination numbera of the two compounds are different. This study has been an attempt to extend Bush's work on totra-pyridinated nickel thiocyanate. If the heats of formation of amine complex salts are to be used comparatively, the coordination numbers of the compounds must be the same. The mean bond strength has been shown to become less as the coordination number in- creases for any one salt. For this reason, only those com- pounds iiavin four coordinated amines could be compared to totrapyridinated nickel thiocyanate. The preparatory work has been an attempt to preparo, where possible, complex salts having a coordination number of four. 3 The basis of comparing heat8 of forrnaton depends on the fact that a stronger bond should have a hiher heat of formation if all other factors ronain constant. The close similarity of the picolines to pyridirie should as a first approximation seem to satisfy the requirement of the con- stoncj of other factors than the hìeats of formation. As the results will show later, this approximation may or may not be justified. If the compounds studied have different crystal structures, the above approximation may be in error enough to invalidate conparison of hcat of formation as a measure of bond strength. Since entropy changes in systems such as those studied are exceedingly difficult to estab- lish, the free energy of formation is not readily obtain- able. ifl order to obtain the heats of formation, an in- direct methoci has been used. It would be impossible to actually form the pure compounds in a calorimeter. Einco, however, the complex compounds arc decomposed readily to the amine hydrochloride and the salt in hydrochloric acid solutions, the calculation of heats of formation was com- paratively simple. If tIie heat of solution of the salt per mole, the heat of solution of the base per mole, 11b and the heat of solution of the complex salt per mole, are own at 250C in 2 N HOi, then the heat of formation at 25°C, ¿ H1, is ivon by the relation: 'i 1i = 1I + - Ji s 4H b c The heats ol' solution have been assumed to be idori- tical with those at infinite dlut1on since sample weights were quite small in comparison to the volume of acid used. 5 PREPARATION OF COLtPOUNDS The preparation and isoltion of numerous pyrldine complex thiocyantes and cyanates as well as many other pyridine cop1ex salts have boon accorp1ishod by previous workers usinç a method based on the high so1ubi1it of these compounds in chloroform. Davis and Loari (4) pre- pared tctrapyrdinatcd nicl:el thiocyanate by d1sso1vin an equivalent amount of nickel sulphate and potassium thio- cyariate in water, adding pyridine sli.ht1y in excezs of the teorotica1 amount and extractiu this mixture with chioro- form. The chloroform extract was evaporated to drrnoss in an air current at room temperature and the tetrapyridinated nickel thiocyanate was deposited as a deep blue crstallne mass. Bush (1) used this procedure for preparing h±s tetrapyridinatod nickel thiocyanate in determining its heat of formation. Since tiio picoliries differ from pyridine only in the presence and position of a methyl croup, ft seemed very likely that their respective complex salts could be prepared by this same procedure. An attempt was also made to pre- paro the complex nickel tiiocyanate of piperdinc, isoquino- line and oi quinoline by this technique. It was found that this methcd was not satisfactory in any of the cases tudiod, The specific results are included in the discus- sion of the respective compounds. NICKEL THIOCYANATE AND o('-PICOLINE Equivalent amount$ of nIckel chloride lioxahydrate and potasiurn tiiiocyanato were dissolved in water and ø.p1o1ino ws added slightly in excess of the quantity theoretically nocesary for four coordination. This aix- turo was extracted with chloroforim, but the nickel salt was not taken up by the chloroform layer quantitatively unless a rather 1are oxces of the base was prosent. This chloro- form solution was creen in contrast to the usual intense blue of nickel amino complexes, When the chloroform was allowed to evaporato, a viscous green seuni was left. There was o evidence of crystallinity. This creen amorphous matter was allowed to stand in the air Í'or a few deys and in that timo the product had laro1y decomposed to yellow nickel thiocyanato. There were, however, a number of brick rod spots throuChout the yoiiow residue which suggested some sort of compound formation with o(-picolino. An alter- nate method was employed to secure this red compound in a pure form. 1ickel thiocyanats was prepared in anhydrous condi- tion by decomposition of the totrapyridinated salt in a well ventilated oven hold at 240 to 260°C for four hours (4, p.2154). The vessel used was large and shallow so that the salt layer was about one half an inch thick.