April 5 , 1953
1735
NOTES
Possible Isomers for Coordination Compounds with Terdentate Ligands and Ligands of Higher Function
and groups of higher function. These are given in Tables I-IV. Optical activity originating within the coordinating groups has been disregarded. Also the customary assumption has been made that adBY W. CONARD FERNELIUS AND BURLE. BRYANT joining points of attachment on the coordinating 17, 1952 RECEIVED OCTOBER groups will always be in the closest adjacent posiIn the consideration of any particular coordina- tions (cis) in the coordination sphere of the metal. Symbofism.-It is customary to use lower case tion compound, it is important to know what isomers are theoretically capable of existence. Main letters to represent unidentate groups and pairs of Smith' has presented tables showing (for both uni- capital letters, bidentate groups: ;.e., AA = a and bidentate groups) the types, classes and iso- symmetrical group like ethylenediamine, the acetymeric forms theoretically expected for entities (com- lacetonate ion, or C204- and AB = an unsymmetripounds or ions) exhibiting coordination numbers cal group like propylenediamine or glycine. In this four (square and tetrahedral) and six (octahedral). paper the symbolism A2 will be used instead of AA. Marchi, Fernelius and McReynolds2similarly have For terdentate groups, A3 = three equivalent A2B = worked out the possible isomeric forms for several points of attachment such as HC(CH2NH2)3, classes of various likely configurations for entities two equivalent positions and one different such as exhibiting coordination number eight with uni- and HN(CH2CH2NH2)z1and ABC = three non-equivabidentate groups. Recently we have had occasion lent positions (possible example is HSCH,CHto work out by means of models the isomeric forms (NH2)COOH). For quadridentate groups AzBz for six-coordinate entities with terdentate groups would represent such groups as (H2NCH2)2CHCH(CH&H)2; ABBA, HzNCHzCHzNHCH2CH2TABLE I NHCHZCHZNH~; and A(B)CD, H2NCH2(HSCH)2ISOMERIC
CLASSES AND FORMS FOR THE OCTAHEDRAL CONCONTAINING TERDENTATE GROUPS
FIGURATION
Class symbol
Type 5 As 3b Aa 2b c Aabcd AzB 3c AzB 2c d AzB c d e ABC 3d ABC 2d e ABCdef Total Type 6 Aa Bz c Aa BC d AzB Cz d A2B CD e ABC Dz e ABC D E f Total
Number of isomeric forms Optically active Optically inactive CiS trans cis trans
.. .. 2
.. 2 6 2 6 12 30
..
.. .. .. ..
1 1
.. 1 1
6
..
2 6 14
..
..
..
1 2 3 1 2 3 1 1
..
..
4
14
..
..
2 2 6 6 12 28
* .
..
* .
1
1
..
..
2 4 6
..
..
1 2 1 2
.. ..
Total
2 3 5 2 5 15
3 9 18 62 2 4 4 8 8 16 42
TABLE I1 ISOMERIC CLASSESAND FORMS FOR A N OCTAHEDRAL CONFIGURATION CONTAINING QUADRIDENTATE GROUPS Class symbol
Type 8 A2Bz 2~ AzBz c d ABBA 2ca ABBA c d AzB(C) 2d A2B(C) d e AzBC 2d AzBC d e A(B)C(D) 2e A(B)C(D) e f A(B)CD 2e A(B)CD e f ABCD 2e ABCD e f Total
Number of isomeric forms Ooticallv ODticallv ictiveiiactiv; cis trans cis trbns
2 4 4 6 4 8 2 8 8 16 6 12 6 12 98
..
..
..
.. .. ..
..
.. ..
.. ..
1 1
..
.. ..
1
.. .. ..
..
..
..
..
Total
2 4 5 7 4 8
..
..
..
..
1
2 2
..
..
3 8 8 16 6 12 7 14
1
3
104
..
.. .. ..
.. ..
..
..
.. ..
Type 9 2 6 2 .. .. 2 A2& G Type 7 A2Ba CD 4 .. .. .. 4 .. 1 1 2 2-41 4 ABBA Cp .. .. .. 4 2AaB 2 .. 1 4 1 ABBA CD 6 .. .. 6 ' 2ABC" 10 2 .. .. 12 4 .. .. AzB(C) Dz .. 4 .. .. 2 1 1 Aa B3 8 A2B(C) DE .. .. .. 8 .. .. 1 1 Ai BaC 2 AzBC Dz 2 .. 1 .. 3 A3 BCD 2 .. .. 1 3 AzBC D E 4 .. 2 .. 6 4 .. .. 1 AzB G D 5 8 .. .. .. A(B)C(D) Ez 8 AzB CDE 6 .. .. 1 7 A(B)C(D) E F 16 .. .. .. 16 ABC D E F 12 2 .. .. 14 A(B)CD Ep 6 .. .. .. 6 A(B)CD EF 12 .. .. .. 12 4 Total 36 4 7 51 ABCD E2 .. 6 .. .. 6 a P. Pfe8er and S. Saure [Ber., 74B, 935 (1941)l have ABCD EF 12 .. , . 12 studied this class t o some extent. Total 94 .. 3 97 (1) J. D. Main Smith, "Chemistry and Atomic Structure," Ernest Benn, Ltd., London, 1924, p. 97. The five isomers of this class have been isolated for di(2) L. E. Marchi. W. C. Fernelius and J. P. McReynolds, THIS ammine( a+'- (o-pheny1enediimino)- di-o-cresolato )cobaltJ O U U ~ A L , 66, 829 (lQ4a); L. E. Marchi, ibid.. 66, 2267 (3943); 06, (111)ion by G. T. Morgan and J . D. Main Smith [I.C h m . 1984 (1944). SOC.,127,913,2030 (1925)]. . t
..
.'
CHNHCH2CHZNHZ. The meaning of the other idty, etc.). Thus, H2NCH2CH(NH2)CH2NH2 in symbols follows from these examples. contrast to ( H Z N C H ~ C H ~ ) may ~ N Hnever be able to Use of Terms cis and trans.-For terdentate cobrdiIiate trans and groups the words cis and trans are used in the same c-)-N=N-c> manner as they are used to designate the isomers of bI 3a 3b; cis indicates that the three points of at\OH HO/ tachment of the polyfunctional ligand are on the may be sufficiently rigid that it will never coordisame face of the octahedron; trans, that they are nate cis. The experimental realization of some of along a plane which passes through the coordination center. For entities with quadridentate the potentialities presented in the tables should not groups, cis and trans refer to the position of the prove too difficult and would contribute greatly to our knowledge of coordination compounds. remaining monodentate ligands. Acknowledgment.-This work was supported Probability of Realizing Theoretical Possibilities. -Some quadri-, quinque- and sexadentate groups by the United States Atomic Energy Commission can be postulated (and even prepared) which are through Contract AT(30-1)-907. OF CHEMISTRY AND PHYSICS not a t all likely to coordinate to a common center. SCHOOL PENNSYLVANIA STATECOLLEGE Certainly for C(CH*NH&, only three of the nitro- THE PENNSYLVANIA STATECOLLEGE, gens can coordinate to a common center; (HZNCH2)&!HCH(CHZNH2) probably will coordinate completely; while cis- 1,2,3,4-~yclobutanetetram-A Polarographic Study of the Zinc Thiocyanate Complexes' ine awaits study to determine whether or not it will coordinate completely. Because of such complicaBY RICHARD E. FRANK^ A N D DAVIDh ' . HUME tions, the classes containing the groups A4 and A3B RECEIVED OCTOBER 21, 1952 are not considered here. If A4 were of the type of phthalocyanine, no isomerism is possible for either Although the thiocyanate complexes of cadmium 31 A4 2b or M A4 b c. Other groups which are dif- and mercury are well known and have been exficult of realization or whose coordination to a com- tensively studied, very little attention has been paid mon center may not be possible are A6, AIB, to complex formation between zinc and thiocyanate XaBa, AzBC, AzBzC, As, &B, A4B2, AhBC, A3B3, ions. The existence of such complex ions is sugA3BSC, A2B2C?and AZBZCD. These have also been gested by the fact that solids such +s K2Zn(SCN)4. omitted. 2H2O have been isolated by Walden.3 The only TABLE I11 published account of an investigation of the ions ISOMERIC CLASSESASD FORMSFOR A N OCTAHEDRAL Cos- in solution is the paper by Ferrell, Ridgion and FIGURATION COXTAINING QUINQUEDENTATE GROUPS RileyP4who obtained potentiometric data which Class Optically Optically suggested the existence of a ZnSCN+ ion with a Type symbol active inactive Total formation constant of the order of 50. Some un10 AIBC~d .. 1 1 published polarographic measurements by DeFord5 ABCBA d 8 .. 8 pointed to the existence of several complexes in AzBC(D) e 2 .. 2 solutions between 0.1 and 2.0 M thiocyanate ion, AzBCD e 4 .. 4 but the measurements were, unfortunately, not A(B)CD(E) f 4 .. 4 made at constant ionic strength, and since the A(B)CDE f 8 .. 8 shifts in half-wave potential observed were of the ABCDE f 12 .. 12 same order of magnitude as those sometimes obTotal 38 1 39 served due to ionic strength effects alone, no quantitative conclusions could be drawn from them. We TABLE IV have, therefore, measured the half-wave potential ISOMERIC CLASSESAND FORMS FOR A N OCTAHEDRAL CONof zinc ion in potassium nitrate-potassium thiocyaFIGURATION CONTAINING SEXADENTATE GROUPS nate mixtures with thiocyanate concentrations Class Optically Optically Type symbol active inactive Total ranging from 0.2 to 2.0 M a t a constant ionic 11 AzBBAz 2 .. 2 strength of 2.0 M . ABCCBA" 8 .. 8 A(B)CC(B)A 0 .. 6 AzBCDz 2 , . 2 AnBCD( E ) 4 , . 4 AIBCDE 4 1 5 A( B)CDE(F) 8 .. 8 ABCDEF 10 .. 10 Total 44 1 45 a An example of this class is being studied by F. P. Dwyer 69, 2917 (1947); 72, 1545 and co-workers, THISJOURNAL, (1950); 74, 4188 (1952).
It seems likely that all groups will not show all the potentialities anticipated for the class to which they belong. Groups may show a preference for certain arrangements because of considerations of steric situations (size, arrangement of atoms, rigid-
Experimental
All measurements were made on a Sargent model 5x1 reThe cording polarograph a t a temperature of 30.0 rt 0.1 dropping electrode was made of marine barometer tubing and had a value of m2/at'/sof 1.355 a t zero applied volts os. the S.C.E. The working anode and reference potential was a saturated calomel electrode which was connected t o the polarograph through a large diameter 2 M potassium nitrate agar bridge. All polarograms were started a t -0.8 v. and run with a span voltage of 0.4 v. in order t o spread out the wave for maximum accuracy of measurement. The initial
.
(1) This work was supported in part by the Atomic Energy Commission. (2) On leave from the University of North Dakota, Grand Forks, North Dakota. (3) P. Walden, 2 . anorg. Chcm., 23, 374 (1900). (4) E. Ferrell, J hf Ridnion and H. L. Riley, J Chrm. Soc., 1121 (193B). (81 I3 I>, DeFord, SI S.Thesis, University of Kunaafi, 1847.
