헥사아자 거대고리 리간드 L(L = 1,8 - 비스(X) - 1,3,6,8,10,13 - 헥사아자시클로테트라데칸(X = 2 - 히드록시에틸 혹은 2 - 시아노에틸)의 니켈(Ⅲ) 착물의 합성 및 특성

김 성 권

(주)세풍 공학연구소

Synthesis and Properties of Ni(Ⅲ) Complexes with Hexaaza Macrocyclic Ligands 1,8 - Bis (2 - hydroxyethyl or 2 - cyanoethyl) - 1,3,6,8,10,13 - hexaazacyclotetradecane

Sung Kwon Kim

Engineering R&D Center, Sepoong Paper Co., Ltd.

1.Introduction

The known oxidation state of nickel spans from +1 to +4. Among these, the most common oxidation state is +2. Thus, the extensive chemistry of nickel(Ⅱ) macrocyclic complexes was known to date. On the contrary to the nickel(Ⅱ) complexes of macrocyclic ligand, the chemistry of nickel macrocyclic complexes with uncommom oxidation states, such as +1 or +3 have been explored to a much lesser degree due to the instability of these complexes. Especially, the purposeful exploration of structure and reactions of Ni(Ⅲ) macrocyclic complexes has most recently been a subject of great intrest. There are of intrest in several points for studying of these complexes: ⅰ) Ni(Ⅲ) macrocyclic complexes are an example with uncommon oxidation state, which were suggested as unstable intermediate in catalytic[1], and electrocatalytic oxidation process[2]. Detection of epr singnal in several nickel - containing enzymes[3], and Ni(Ⅲ) or Ni(Ⅰ) species have been implicated as a catalytic transient in these enzyme. ⅱ) The complexes of Ni(Ⅱ) and Ni(Ⅲ) with an identical ligand enviroment have used in order to test model for the rate constant k for an electron - exchange reaction[4].

Macrocyclic ligands are often known to allow metal complexes in which uncommon oxidation states of the metal ions are stabilized. And thus, some of Ni(Ⅲ) macrocyclic complexes have been synthesized, mostly in situ, and their magnetic moment, electronic absorption and epr spectra have been measured[5,6]. However, structural(e.g. X-ray structure of Ni(Ⅲ) macrocyclic complexes) information and reactions with organic substrates are rather scare. This is because only a very limited number of such complexes have been isolated as solids. Therefore, we have been interested in the synthesis of a series of low-spin octahedral Ni(Ⅲ) macrocyclic complexes of the form [NiⅢL(Y)2]+, where L = L1 or L2, and Y = Cl, Br, and NO3.

We report the synthesis and characterization of the Ni(Ⅲ) complexes of macrocyclic ligands L1 or L2 in this paper.

2. Experimental

Reagents: All chemicals in the synthesis were of reagent  grades,  and

were purified according to the literature[7]. All solvents used to the reactions of the complexes and the spectroscopic measurements were purified. Ni(Ⅱ) complexes of L1 and L2 were prepared according to the method given by Kim et al[8].

Measurements: Infrared spectra were recorded with a JASCO IR - 810 and a Perkin - Elmer 782 spectrophotometer in the range 4000 - 400 cm-1. Samples were prepared as Nujol mull or KBr pellets. Conductance measurements were performed by using an TOA conductivity meter CM - 30 ET in conjunction with a conductivity cell with cell constant of 1.0 cm-1. Magnetic susceptibilities of solid samples were measured at room temperature by the standard faraday method using faraday type balance. Cyclic voltametry was carried out with EG&G, PARC Model 173 cyclic voltammograph coupled with a Kipp & Zone X - Y recorder. Electronic absorption spectra were obtained on a shimadzu 260 UV/vis spectrophotometer. Elemental analysis were performed by Instrumental Analysis Center, Seoul National Universty and Korea Basic Science Center.

Systhesis: Safty Note. Caution! Perchlorate salts of metal complexes with organic ligands are potentially explosive. Only small amounts of material should be prepared, and these should be handled with great caution.

[NiⅢL1Br2]ClO4: To a stirred aqueous solution of [NiⅡL1](ClO4)2(2.0 g) was slowly added (NH4)2S2O8(0.5 g) dissolved in a minium amount of water. The color of the mixture turned green instantly. To this green solution was slowly added dropwise concentrated hydrobromic acid with stirring, and then dark-red brown crystals fromed on cooling. The crystals were filtered off, washed with methanol, and dried in vacuo. Yield: - 45%. Anal. Calcd. for NiC12H30N6Br2ClO6: C, 22.36; H, 5.31; N, 13.04. Found: C, 22.11; H, 4.83; H, 13.06.

[NiⅢL1Cl2]ClO4: This compound was prepared by a method similar to that for [NiⅢL1Br2]ClO4 except that concentrated HCl was used instead of concentrated HBr. The compound was red-brown crystals. Yield: - 10%. Anal. Calcd. for NiC12H39N6Cl3O6.H2O: C, 26.81; H, 6.00; N, 15.63.  Found: C, 26.30; H, 5.76; N, 15.38.

[NiⅢL2(NO3)2]ClO4: 2.0 g of green [NiⅡ(L2)](ClO4)2 was dissolved in 5.0 ml of conc. HNO3. The solution immedietely turned dark green. To this solution, 8.0 ml of H2O or CH3CN was slowly added with stirring, and dark-red crystal formed on cooling. The product was filtered off, washed with methanol, and dried in vacuo. Yield: - 15%. Anal. Calcd. for NiC14H28N10ClO10: C, 28.47; H, 4.70; N, 23.72. Found: C, 28.32; H, 4.48; N, 23.32.

3. Results and Discussion

Oxidation of Ni(Ⅱ) complexes of macroclic ligands L1 or L2 with oxidizing agents[(NH4)2S2O8 or HNO3] in H2O or CH3CN solutions produced Ni(Ⅲ) macrocyclic complexes. Conductance, Infrared, and Electronic spectra of the complexes were measured, amd the data are summarized in Table Ⅰ. The magnetic moments and epr spectral data are presented in Table Ⅱ.

Table Ⅰ. Physical Properties of the Ni(Ⅲ) Complexes[Ni(Y)2]ClO4

□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□

L  Y	ira	electronic spectra	□M

□NH, cm-1	□max, nm(□M-1cm-1)	□-1cm-2M-1

□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□

L1 Br	3150(3210)   757(94)b,  382(7580)b,  290(10600)b	48.7c, 170.9b

L1 Cl	3150(3210)   777(36)c,  318(12200)c, 287(11800)c  31.2c

L2 NO3	3185(3275)   710(sh)b,  297(13000)b, 215(14700)b  143.6b

□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□

aMeasured with Nujol mull, bMeasured in MeCN, cMeasured in Me2SO

(  ) : N-H stretching frequencies(□NH) of Ni(Ⅱ) macrocyclic complexes

Table Ⅱ. Magnetic Moments and Epr Data for the Ni(Ⅲ) Complexes[NiL(Y)2]ClO4

□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□

L	Y	□eff,BM	EPR data

g1a	g2a	g3a	gsolution

□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□

L1	Br	1.90	g1 = 2.175, g2 = 2.123, g3 = 2.081     gav = 2.118a

L1	Cl	1.89	g1 = 2.179, g2 = 2.128, g3 = 2.179     gav = 2.126b

L2	NO3	1.93	g□ = 2.210,       g□ = 2.060     gav = 2.151a

□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□

aMeasured with powder samples at room temp. bMeasured in MeCN,

cMeasured in Me2SO

Systhesis: The reddish-brown [NiⅢL1Cl2]ClO4 and dark-red [NiⅢL1Br2]ClO4 were prepared form the reactions of [NiⅡL1](ClO4)2 with ammomiumpersulfate in water, followed by adding conc. HCl for [NiⅢL1]ClO4 or conc. HBr for [NiⅢL1Br2]ClO4, respectively. The dark-red Ni(Ⅲ) complexes [NiⅢL2(NO3)2]ClO4 were synthesized by dissolving the Ni(Ⅱ) complex of L2 conc. HNO3 followed by diluting with water or acetonitrile solutions.

Properties and Spectra: The Ni(Ⅲ) macrocyclic complexes, [NiⅢL(Y)2]ClO4(L = L1 or L2, Y = Cl, Br, or NO3), are a few soluble in MeCN, and Me2SO, but insoluble in alcohols. All Ni(Ⅲ) complexes are very stable in the crystalline state in dry air, but extremery unstable in aqueous solutions. The value of molar conductance(Table Ⅰ) for the Ni(Ⅲ) macrocyclic complexes indicates that the complexes are 1 : 1 type electrolytes. The IR spectra of the complexes show a single absorption attributed to N-H strech of coordination secondary amines at around 3150 cm-1. The values of □NH are much higher for the Ni(Ⅱ) complexes of the ligand(L1 or L2)(around 3210 cm-1) than those for the Ni(Ⅲ) complexes of the ligand(L1 or L2), indicating that Ni-N interactions in Ni(Ⅱ) complexes are stronger than that in NI(Ⅲ) complexes. In order to establish the authenticity of these Ni(Ⅲ) complexes as low-spin d7 Ni(Ⅳ) state rather than Ni(Ⅱ) ligand-oxidized radical species, epr spectroscopy has been used extensively. The majority of the oxidized products(Ni(Ⅲ) complexes) exhibit anisotropic axial symmetry, with g□ > g□ and a value of considerably greater than 2[9]. These are consitent with the existence of a low-spin d7 six coordiate Ni(Ⅲ) tetragonally distorted octahedral geometry with elongation of the axial bonds. The most probable electronic configuration for a low-spin d7 Ni(Ⅲ) complex with D4H symmetry is (eg)2(b2g)4(a1g)1, indicating that the unpaired electron is in dz2 orbital[10]. The solid sample of Ni(Ⅲ) complexes show anistropic rhombic epr spectra for ligand system L1 and anisotropic axial symmetry for L2. The anisotropic axial spectra giving g□ values greater than g□ and the rhombic spetra showing g1, g2 and g3 values indicate that the complexes are in the form of typical d7 electronic configuration with an unpaired electron in the dz2 orbital of the distorted tetragonally octahedral Ni(Ⅲ) complexes. The electronic spectra of this compleses reveals the near-i.r region, indicating the presence of a relatively weak ligand-field band. This is consistent with the presence of an electron in the dz2 orbital such that the transition from this orbital to the dy2 - dz2 orbital(2A1g --> 2B1g) will occur at much lower than the transitonal energy originating from either the dxy or dxz, dyz orbitals in low spin complexes of FeⅢ, CrⅢ, and CoⅢ, the ligand-field band of which usually occur in the visible region[11]. In this study we have presented strong evidence for the existence of the Ni(Ⅲ) oxidation state in a teteagonally distrorted octagedral ligand field.

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