PIPERIDINATE COMPLEXES OF KICKELA N D COPPERMESOPORPHYRIN IX
Nov. 5 , 1964
magnetically dilute single crystals of known structure, we have concluded t h a t the probable ground-state vacancy configurations are 1 e > , I e*y>, E ? Y > , and 'C*O>, respectively. In n z h symmetry, E = d,,, y d,,, and 0 E daZ2- y z . The z-axis is perpendicular to the molecular plane, and the y-axis bisects each ligand. The configurational excitation energies predicted from spin-Hamiltonians have been compared with the optical spectra of solutions of the complexes, and observed weak transitions were assigned. The agreement between predicted and observed optical transition energies is satisfactory considering the uncertainty in the spinorbit coupling parameter, {, for the complex. From the value of and { required to fit the hyperfine structure, and the optical transition energies of the cobalt complex, the d-orbitals are considerably less covalent in this complex than in the other three. In the other complexes, the hyperfine structure of the paramagnetic resonance and the optical spectra are best fit with r+ and { about 0,5-0.6 of the calculated free ion values. \Ye find that the strength of the tetragonal field of maleonitriledithiolate dianion as measured by the onep (where p = dZ2- v 2 ) is large, this electron energy E energy difference being estimated in the region of 40,000 cm.-' for the copper, nickel, and cobalt complexes. The parameter giz is reduced in CHC13-DMF glass of [?jiS1C4(CN)4]-below its value in the single crystal. According to the theory this implies a reduction in the parameter cl, or in c3. Since c1 refers to the excitation le*y> 1 c 2 0 > , whereas c3 refers to ~ E * Y > ) e ? p > , i t is more reasonable that the solvent would affect the energy of the former excitation, which ap-
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pears to be increased by the order of 10% in the glass over its value in the single crystal. The common feature of our interpretation of the electronic configurations of the d3-hole complexes is the proximity of the energies of the configurations j ~ ~ y > and 1 E * O > . The splitting is largest in the nickel(II1) complex, with ie?y> lower (by about 20,000 cm.-l), smaller in the cobalt(I1) complex (-350(1 cm.-I), and the E ~ O > has become the ground-state configuration in the rhodium(I1) complex (with l k y > a t about 8000 cm.-I). No reliable estimate can be obtained of the energy of the e2x> configuration from the theory, but i t may be stated that the energy of this configuration is well above that of e 2 y > , probably by > 15,000 cm.-'. The large splitting of !e*y> and 1e2x> implies an extensive interaction of the metal 1y> and Ix> orbitals with rr-orbitals of the ligands. Finally, molecular orbital calculations of the groundstate configurations of [KiS4C4(CN)4]- and [Cos4C4(CN)d]-*using the extended Huckel theory correctly predict the 1 e2y> c o n f i g ~ r a t i o n . ~ ~ Acknowledgments.-Support of this work by the National Science Foundation through grants GP-957 and GP-596, the -4dvanced Research Projects Agency (Department of Defence) through Contract SD-XS, and the Milton Fund of Harvard University is gratefully acknowledged. \Ye wish to thank Professor D . H . Templeton and his associates for informing us of the results of their crystal structure determinations prior to publication. \Ye also thank Mr. A. Kwok for engaging in many helpful discussions.
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(32) R. Hoffmann a n d R. H . Holm, unpublished work.
CHEMICAL LABORATORIES OF THEJOHNS HOPKIXSCXIVERSITY, BALTIMORE, M A R Y L A X D2 12181
Piperidinate Complexes of Nickel and Copper Mesoporphyrin IX'
w.BAKER,LTAURICE s. BROOKHART, A N D ALSOPH H . CORWIN
BY EARL
RECEIVED FEBRUARY 15, 1964 By spectrophotometric techniques, it is shown t h a t copper and nickel mesoporphprin IX form, respectively, a mono- and a dicomplex with piperidine. The thermodynamic constants for these reactions are reported T h e crystal field stabilization energy of the structure of the transition metal ion is correlated with t h e struct u r e of metalloporphyrin ligand comple\es and a relationship of spectral shifts t o ligand number is shown
T h e formation of complexes of copper and nickel mesoporphyrin with a variety of ligands was reported by Corwin, Whitten, Baker, and Kleinspehn.2 Previously, Caughey, Deal, McLees, and Alben3 had shown that nickel porphyrins form complexes with pyridine. Miller and Dorough studied the formation of pyridine complexes of several metallo derivatives of tetraphenylporphine and reported equilibrium constants of their formation. This article reports a spectrophotometric study of the reaction of piperidine with copper and nickel meso( 1 ) Pol-phyi-in Studies. X X X I I . Papet- X X X I : E. W. Baker, hl. Iluccia, and A. H . Coi-win, A n a l . Riochem., 8, 5 1 2 (1964) This work was supported in pat-t b y Reseal-ch G r a n t A-2877 from t h e S a t i o n a l Institutes of Health and in pal-t b y t h e Petroleum Reseal-ch F u n d administered by t h e American Chemical Society. Presented in part a t t h e 146th Xational hleeting of t h e American Chemical Society, Denver. Colo., 1961. 12) A H Coi-min, D. G . W h i t t e n , E. W. Baker, and G . G . Kleinspehn, J . A m . ( h e m . Soc., 86, 3621 (1963). 13) W .S. C a u g h e y , R . 31. Deal, B . D . McLees, and J 0. Alben, ibi
