Synthesis and properties of μ-cyano(phthalocyaninato)-rhodium(III)

Synthetic Metals, 10 (1985) 357 - 363

357

SYNTHESIS AND PROPERTIES OF p-CYANO(PHTHALOCYANINATO)RHODIUM(III) MICHAEL HANACK* and XAVER MUNZ

Institut fiir Organische Chemie, Lehrstuhl fiir Organische Chemie II, A u f der Morgenstelle 18, D-7400 Tiibingen (F.R.G.) (Received December 20, 1984)

Abstract This contribution reports on the synthesis of p-cyano(phthalocyaninato)rhodium(III), [PcRhCN]n (1), by splitting off potassium cyanide from potassium(dicyano)phthalocyaninatorhodium(III), K[PcRh(CN):] (2). Monomeric complexes, PcRh(L)CN (7), were formed when [PcRhCN]n (1) was treated with base molecules L, such as n-butylamine and pyridine. All compounds were characterized by IR, far-IR spectroscopy, thermal and elemental analyses, and partly by UV, 1H-NMR and FD (field desorption) mass spectroscopy. The undoped polymer [PcRhCN]~ (1) exhibits a d.c. dark conductivity of 4 × 10 -4 S/cm, which was diminished by eight orders of magnitude when the polymeric structure was decomposed by treatment with a competing ligand. Recently we reported on the synthesis and conductivities of polymeric p-cyano(phthalocyaninato)metal compounds [PcMCN], (M = Co, Fe, Mn, Cr), among which [PcCoCN], showed a remarkably high room temperature conductivity of OaT = 2 × 10 -2 S/cm without additional doping [1, 2]. We now document here the preparation and conductivities of #-cyano(phthalocyaninato)rhodium(III), [PcRhCN]n (1), a homologue of [PcCoCN]n, to find out whether or not a change of the central metal atom from cobalt to rhodium significantly affects the properties of the system. As in the case of [PcCoCN]n [1], a possible route for the synthesis of [PcRhCN], (1) could be the removal of KCN from potassium(dicyano)phthalocyaninatorhodium(III), K[PcRh(CN)2] (2). Both PcRhC1 (3) and PcRh(DMA)C1 (4) (DMA = dimethylamine) are starting materials for the synthesis of 2. In the case of cobalt, the corresponding complex K[PcCo(CN)2 ] (5) cannot be prepared from PcCoC1 since the latter does not exist. However, 5 has been obtained by the reaction of PcCoCI: and KCN in boiling ethanol [1, 2]. The complex K[PcCo(CN):] (5) is also synthesized starting from PcCo by in situ oxidation with oxygen in the presence of excess cyanide [1, 2]. *Author to w h o m correspondence should be addressed. 0379-6779/85/$3.30

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358

The synthesis of the rhodium analogue PcRhC1 (3) has been reported in 85% yield from o-cyanobenzamide and RhC13"3H20 [3]. PcRh(DMA)C1 (4) has been obtained from Li2Pc and RhCI3.3H20 in DMF [4]. We have now prepared the soluble potassium(dicyano)phthalocyaninatorhodium(III), K[PcRh(CN)2] (2), starting from both PcRhC1 (3) and PcRh(DMA)C1 (4) by reacting with KCN in acetone. 2 is characterized by IR, FIR, UV/VIS and 1H-NMR spectroscopy, as well as by elemental and thermal analyses. The IR spectrum of 2 exhibits a CN valence frequency at 2130 cm -1, which is in the anticipated region for terminal Rh(III)-cyano groups [5] and is similar to the CN frequency for the cobalt complex 5 (2130 cm -l) {Table 1). TABLE 1 CN valence frequencies [cm -1] of several [K(PcM(CN)2)] and [PcMCN]n [1, 2]

K[PcM(CN)2] [PcMCN] n

Rh

Co

Mn

Cr

2130 2160

2130 2158

2114 2133

2133 2150

The 1H-NMR spectrum of K[PcRh(CN)2] (2) is in agreement with the proposed structure {Table 2) and is practically identical with the cobalt complex 5 [1, 2]. The FIR spectrum of 2 shows a sharp, very intense band at 348 cm -1. The elemental analysis of 2 is in accordance with the given stoichiometry, but 2 contains two moles of water yielding a composition of K[PcRh(CN)2].2H20. The solvent molecules of 2 are removed endothermically between 40 and 120 °C during simultaneous TG/DTA measurements. A further endothermic mass loss between 220 and 295 °C corresponds to the loss of one cyanide group. Between 320 and 440 °C, the second cyanide group is split off. This behaviour is somewhat different from the cobalt compound 5, in which only one cyanide group is removed endothermically at about 300 °C. At higher temperatures (>300 °C), the removal of the second cyanide group leads to a substitution on the aromatic ring [1, 2]. [PcRhCN], (1) is formed by treating K[PcRh(CN)2] (2) with boiling water for 72 h, thereby removing one mol of KCN from 2. Figure 1 illustrates 1 but contains no structural details. 1 is characterized by IR and FIR spectroscopy, elemental analysis and thermal decomposition. The CN valence frequency of 1 appears at 2160 cm -1. Compared with the monomeric complex 2, the maximum is shifted about 30 cm -1 to higher energy {Table 1), which is taken as evidence for a cyano bridged structure in 1 [6]. The CN valence frequencies in the IR spectra of several monomers and [PcMCN], are compared in Table 1. The thermal decomposition of [PcRhCN], (1) between 200 and 350 °C shows a mass loss of 3.7% (calc. 4.0%), corresponding to the loss of one cyanide group. The thermal decomposition starts at 70 °C with a removal of 1.5 mol of H20/mol of complex.

359

CN . . . . . .

Fig. 1. [ P c R h C N ] n (1).

According to the ESR spectrum, [ P c R h C N ] , (1) shows no indication of the presence of Rh 2+, contrary to [PcCoCN], which does contain some Co 2+ [1,2]. [ P c R h C N ] , (1) is isostructural with [PcCoCN], as demonstrated by powder X-ray diffraction studies. 1 is insoluble in non-coordinating solvents. The polymeric structure is destroyed, however, and monomeric complexes PcRh(L)CN (7) are formed when 1 is treated with a competing ligand e.g., with bases (L) such as pyridine (py) and n-butylamine (ba) (Fig. 2). L =N N

.__.~-~

..~ Rh.~

N

L "~_~S--.~

C ill N F i g . 2 . 7 a , L = ba; 7b, L = py.

The monomers 7 are characterized through IR and mass spectroscopy as well as by elemental and thermal analyses. The 1H-NMR spectrum of PcRh(ba)CN, which shows the characteristic shielding feature of the axial baligand, supports the suggested structure {Table 2). The IR data for 7 exhibit a slight increase in the CN valence frequency with decreasing o
360 TABLE 2 1H-NMR data of K[PcRh(CN)2] and PcRh(ba)CN Compound

1H-NMR

K[PcRh(CN)2] a'b (2)

H-1 H-2

PeRh(ba)CN a'c (7a)

H-1 H-2 N-H (ba) Cc~,~,7,a-H (ba)

6 (ppm) 8.2 (m, 8H) 9.5 (m, 8H) 8.2 9.5 --2.6 --0.3

(m, 8H) (m, 8H) (s, 2H) --1.2 (m, 9H)

aAA'BB' pattern. These protons are assigned in Fig. 2. bin acetone-d 6. CIn CDC13.

comparison with a weaker o-donor ligand with lr acid properties (e.g., py) which increase the acidity, a strong o-donor brings about a lower CN valence frequency (Table 3). Further support for the polymeric structure of [PcRhCN], (1) arises from additional IR investigations. The combination of the Rh--C and CN bond strengths estimated from IR and FIR spectra in complexes with terminal CN groups as far as we know is not known in compounds with bridging CN ligands. The increase in CN bond strength discussed above is accompanied by a decrease of the Rh--C bond strength [ 6 ]. This feature is shown for the Rh-C frequency in the far-IR spectra of the monomeric PcRh(L)CN complexes and the corresponding polymer [PcRhCN]n [1] (Table 3). The increase of the CN valence frequency in the IR spectrum of [PcRhCN]n (1), together with the thermal stability and the stoichiometry, suggest the formulation of this compound as a cyanide-bridged polymer. PcRh(ba)CN (7a) and PcRh(py)CN (7b) show different behaviours under thermal decomposition. 7a decomposes between 70 and 260 °C with removal of n-butylamine. The cyanide group is split o f f between 270 and 410 °C. The thermal decomposition of 7b begins at 75 °C with the removal of the CN group and then, between 190 and 290 °C, pyridine is lost. The d.c. dark conductivity of 1 is determined with an apparatus [8] for the measurement of powder conductivities according to the four-probe van der Pauw technique under 1 kbar pressure. [PcRhCN]n (1) exhibits an electrical conductivity of o -- 4 × 10 -4 S/cm without additional doping. It shows semiconducting behaviour, the activation energy being 0.3 eV. The conductivity of 1 is only slightly increased by doping with iodine. Doping of [PcRhCN]n by grinding with an excess of iodine in the presence of a few drops of benzene leads to [(PcRhCN)I0.32]n(which exhibits a conductivity ORT ----8 × 10 -4 S/cm. When the polymeric structure of [PcRhCN], is destroyed by treatment with a competing ligand, e.g., to form PeRh(ba)CN (7a) the conductivity is diminished by eight orders of magnitude (Table 4).

361 TABLE 3 IR data and thermal stabilities for PcRhCN-complexes Compound

PCN

PRh--C

[PcRhCN] n (1) K[PcRh(CN)2 ] (2) PcRh(ba)CN (7a)

2160 2130 2140

332/352 348 373

PcRh(py)CN

2145

384

(7b)

Thermal decomposition 2 0 0 - 3 5 0 °C 2 2 0 - 4 4 0 °C 7 0 - 4 1 0 °C

75 - 290 °C

TABLE 4 Powder conductivities a of PcRh(III) derivatives Compound

GRT a ( S / c m )

Ea

[PcRhCN]n (1) K [ P c R h ( C N ) 2] ( 2 ) PcRh(ba)CN (7a)

4 × 10 - 4 b 3 × 10 -9 c 2 × 1 0 -12 c

0.3 eV _ __

apressure: I0 s Pa (i kbar). bFour-probe technique. CTwo-probe technique.

Experimental section Chlorodimethylamino(phthalocyaninato)rhodium(III) (4) is prepared by the m e t h o d described by Berg [4]. Routine infrared spectra are obtained on a Perkin-Elmer 398 as Nujol mulls. The FIR spectra are obtained on a Bruker IFS 114c as polyethylene (PE) pellets. The 1H-NMR spectra are recorded on a Bruker HX 90 apparatus. The UV/VIS spectra are recorded on a Beckman Acta MVII spectrometer and the mass spectra are obtained on a Varian MAT 711 mass spectrometer by the direct inlet and FD technique. Thermogravimetric measurements are made on a Netzsch STA Model 429 and 409 under nitrogen at a heating rate of 2 °C min-1.

Chloro(phthalocyaninato)rhodium(III), PcRhCl (3) RhCI3"3H20 (1.8 mmol), o-cyanobenzamide (17.8 mmol) and anthracene (12.6 retool) are heated together at 280 °C for 1 h under nitrogen. The crude product is crushed in a mortar and extracted with ethanol using a Soxhlet apparatus (12 h), toluene (6 h) and acetone (36 h). The dark blue residue is dried at 110 °C after washing with ether (yield 85%). Mass spectrum (FD): re~e= 615; TG (dissociation range °C, mass decrease): 2 8 0 - 410 °, 5.9%; FIR (PE): v = 330 cm-1; UV/VIS (DMF): ;~ = 644, 344 nm; Ca2H16NsRhC1 (650.90): C 59.05; H 2.48; N 17.22; Cl 5.45; found: C 57.90; H 2.75; N 18.21; C1 5.03.

362

Potassium(dicyano)phthalocyaninatorhodium(III),

K[PcRh(CN):]. 2H20,

(2) A suspension of 1.1 g (1.7 mmol) PcRhC1 and 1.6 g (25.5 mmol) KCN in 150 ml acetone is refluxed for 72 h under nitrogen and filtered. After evaporation of the acetone, the residue is washed several times with water. The resulting microcrystalline red-blue powder is dried under high vacuum, yielding 0.68 g (57%) of product. PcRh(DMA)C1 (4) is also treated with KCN in acetone as described above to give K[PcRh(CN)2]'2H20 (2) (yield 70%). Infrared spectrum (Nujol mull): v = 2130 cm -1 (m); 1H-NMR (acetoned6): 5 = 8.2 (m, 8H), 9.5 ppm (m, 8H); FIR (PE): v = 348 cm-1; UV/VIS (DMF): k = 651, 343 nm; TG (dissociation range °C, mass decrease): first step, 40 - 120 °, 4.3%; second step, 220 - 295 °, 4.1%; third step, 320 - 440 °, 4.5%; C3aH16N10RhK.2H20 (742.60): C 54.99; H 2.71; N 18.86; K 5.14; found: C 54.77; H 2.59; N 18.43;K 4.65.

p-Cyano(phthalocyaninato)rhodium(I11), [PcRhCN]~. 1.5H20 (1) [PcRhCN]~ (1) is prepared by boiling K[PcRh(CN)2] with water for 72 h. Extraction with acetone separates unreacted K[PcRh(CN)2], yielding the blue product (yield 88%). Infrared spectrum (Nujol mull): v = 2160 (m), 2140 cm -1 (w); TG (dissociation range °C, mass decrease): first step 70 - 200 °, 4%; second step, 200 - 350 °, 3.7%; mass spectrum (inlet temperature 200 °C): m/e = 52, 615; C33H16N9Rh" 1.5H20 (668.47): C 59.29; H 2.86; N 18.85; found: C 58.05; H 2.34; N 17.97. Cyano(phthalocyaninato)rhodium(III) base adducts, PcRh(L)CN (Ta, b) L = n-butylamine (ba), pyridine (py) [PcRhCN]n is stirred in the pure ligand at 100 °C for 3 days. The solution is cooled and filtered. The resulting powder is dried under vacuum, yielding the products PcRh(ba)CN (7a) and PcRh(py)CN (7b). 7a: Infrared spectrum (Nujol mull): v = 2140 cm -1 (w); TG {dissociation range °C, mass decrease): first step 70 - 260 °, 10.5%; second step 260 410 °, 5.4%; FIR (PE): v = 373 cm -1 (m); 1H-NMR (CDC13): 5 = 8.2 (m, 8H), 9.5 (m, 8H), --2.6 (s, ba N--H), --0.3 to 1.2 ppm (m, ba C--H); mass spectrum (FD): m/e = 641; UV/VIS (DMF): k = 650, 345 nm; C37H27N10Rh (714.60): C 62.19; H 3.81; N 19.60; found: C 61.47; H 3.48; N 18.53. 7b: Infrared spectrum (Nujol mull): v = 2145 cm -1 (w): TG (dissociation range °C, mass decrease): first step 75 - 170 °, 4.2%; second step 190 290 °, 10.4%; FIR (PE): v = 384 cm-1; CasH21N10Rh (720.56): C 63.34; H 2.93; N 19.44; found: C 60.86; H 2.75; N 17.78. Acknowledgement Financial support of the 'Stiftung Volkswagenwerk' is gratefully acknowledged.

363 References 1 2 3 4 5 6

J. Metz and M. Hanack, J. Am. Chem. Soc., 105 (1983) 828. A. Datz, J. Metz, O. Schneider and M. Hanack, Synth. Met., 9 (1984) 31. J. M. Keen and B. W. Malerbi, J. Inorg. Nucl. Chem., 27 (1965) 1311. Th. H. Berg, Diss. Abstr. Int. B., 43 (1982) 1092. J. B. Baranovskii, Russ. J. Inorg. Chem., 14 (1969) 115. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, Wiley, N e w York, 1963. 7 K. F. Purcell,J. Am. Chem. Soc., 89 (1967) 248. 8 W. Kobel, O. Schneider, K. Seelig and M. Hanack, unpublished results.