Synthesis and Spectral Properties of Phenyl‐Pyridin‐2‐Ylmethylene‐Amine Complex of Rhodium(III)

Abstract

A new com plex of [Rh(PA)2Cl2]Cl·H2O (where PA = phenyl-pyridin-2-ylmethylene-amine) has been synthe sized and char ac ter ized. The com plex shows high in ten sity bands in the UV re gion, and these are as signed to spin-allowed -* tran si tions. The me dium-intensity ab sorp tion band pro file in the lower en ergy re gion can be ex plained by con vo lu tion of spin-allowed CT and d-d* tran si tions. Emis sion spec trum at low tem per ature (77 K) of the com plex in EtOH/MeOH (4:1 v/v) has also been in ves ti gated. It shows a broad, sym met ric, and structureless red emis sion with mi cro sec ond life time and hence is as signed as d-d* phos p ho res cence. Voltammetric data have also been ob tained for the com plex. There were three re duc tion peaks ob served for the com plex. The first peak, in clud ing two re duc tion steps with elim i na tion of two chlo rides, is con sis tent with ECEC re ac tion. IN TRO DUC TIONThe syn thetic pro ce dures of phenyl-pyridin-2-yl methyl ene-amine (PA), a Schiff base ligand, have been re ported ear lier.1 Syn thetic stud ies in volv ing complexation of PA have been re ported for some tran si tion met als such as Ag(I), PA is an un sym met ri cal bidentate ligand and thus al lows it to form metal com plexes of var i ous co or di na tion struc tures. 5 In the pres ent work, we have first fo cused on prep a ra tion of the rho dium(III) com plex co or di nated with two PA lig ands. In or der to get a closer un der stand ing of bond ing in forma tion in co or di na tion chem is try, we have also ex am ined the tran si tion types through the ob served elec tronic spec tra from photophysical prop er ties of the PA com plex pre pared at this lab. Elec tro chem i cal stud ies of this newly syn the sized complex have been car ried out with the aim to get com par a tive and sup ple men tary in for ma tion in con trast to those ob tained via emis sion spec tros copy in clud ing lu mi nes cence data. RE SULTS AND DIS CUS SIONThe base peak in mass spec trum of the com plex is m/z = 537, con sis tent with the mo lec u lar mass of [Rh(PA)2Cl2] + .The in fra red spec trum of [Rh(PA)2Cl2] + ex hib its the (C=N) band in the vi cin ity of 1600 cm -1 . This fre quency is slightly smaller than that in the free PA ligand (ca 1625 cm -1 ) and is in ac cord with the ru the nium an a logue, Ru(PA) 2 Cl 2 . 5a The complex shows two ad di tional bands near 343 and 325 cm -1 , which were not ob served in the free PA ligand, had been assigned to the Rh-Cl stretch ing. 11 More over, the dou blet nature of Rh-Cl stretch ing in di cates that the two chlo rides are cis to each other. 12The pro ton NMR spec trum ac quired for the com plex reveals 8 unequivalent pro tons and the 13 C spec trum ex hib its 10 car bon res o nance sig nals. Ac cord ing to these NMR data, the two PA lig ands are chem i cally equiv a lent in [Rh(PA)2Cl2] + . There are 3 pos si ble iso mers for cis-[Rh(PA) 2 Cl 2 ] + de duced from the two-PA co or di nated com plexes as dis played be low.In the cis-iso mer, two PA lig ands are not...