The reactions between Mn(Por)CI and Bu4N+CN- have been examined in various solvents by UV-vis and H-1 NMR spectroscopy, where Por's are dianions of meso-tetraisopropylporphyrin ((TPrP)-Pr-i), meso-tetraphenylporphyrin (TPP), meso-tetrakis(p-(trifluoromethyl)phenyl)porphyrin (p-CF3-TPP), meso-tetramesitylporphyrin (TMP), and meso-tetrakis(2,6-dichlorophenyl)porphyrin (2,6-CI2-TPP). Population ratios of the reaction products, Mn(Por)(CN) and [Mn(Por)(CN)(2)](-), have been sensitively affected by the solvents used. In the case of Mn(TiPrP)CI, the following results are obtained: (i) The bis-adduct is preferentially formed in dipolar aprotic solvents such as DMSO, DMF, and acetonitrile. (ii) Both the mono- and bis-adduct are formed in the less polar solvents such as CH2CI2 and benzene though the complete conversion to the bis-adduct is achieved with much smaller amount of the ligand in benzene solution. (iii) Only the mono-adduct is formed in CHCI3 solution even in the presence of a large excess of cyanide. (iv) Neither the mono- nor the bis-adduct is obtained in methanol solution. The results mentioned above have been explained in terms of the C-H...N and O-H...N hydrogen bonding in chloroform and methanol solutions, respectively, between the solvent molecules and cyanide ligand; hydrogen bonding weakens the coordination ability of cyanide and reduces the population of the bis-adduct. The importance of the C-H...N weak hydrogen bonding is most explicitly shown in the following fact: while the starting complex is completely converted to the bis-adduct in CH2CI2 solution, the conversion from the mono- to the bis-adduct is not observed even in the presence of 7000 equiv of Bu4N+CN- in CHCI3 solution. The effective magnetic moments of the bis-adduct has been determined by the Evans method to be 3.2 mu(B) at 25degreesC, suggesting that the complex adopts the usual (d(xy))(2)(d(xz), d(yz))(2) electron configuration despite the highly ruffled porphyrin core expected for [Mn(TiPrP)(CN)(2)](-). The spin densities of [Mn(TiPrP)(CN)(2)](-) centered on the pi MO have been determined on the basis of the 1H and C-13 NMR chemical shifts. Estimated spin densities areas follows: meso-carbon,-0.0014; alpha-pyrrole carbon, -0.0011, beta-pyrrole carbon, +0.0066; pyrrole nitrogen, -0.022. The spin densities at the pyrrole carbon and meso nitrogen atoms are much smaller than those of the corresponding [Mn(TPP)(CN)(2)](-), which is ascribed to the nonplanar porphyrin ring of [Mn(TiPrP)(CN)(2)](-). This study has reveled that the C-H...N weak hydrogen bonding is playing an important role in determining the stability of the manganese(III) complexes.