Vibrational spectroscopic and thermal studies of some 3-phenylpropylamine complexes

Vibrational Spectroscopy 51 (2009) 299–307

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Vibrational spectroscopic and thermal studies of some 3-phenylpropylamine complexes ¨ nal a,*, S¸u¨kru¨ S¸entu¨rk b, Mustafa S¸enyel a Arslan U a b

Department of Physics, Science Faculty, Anadolu University, 26470 Eskis¸ehir, Turkey Department of Physics, Dumlupinar University, Ku¨tahya, Turkey

A R T I C L E I N F O

A B S T R A C T

Article history: Received 7 April 2009 Received in revised form 17 August 2009 Accepted 17 August 2009 Available online 22 August 2009

Four new Hofmann–3-phenylpropylamine (3PPA) type complexes with chemical formulae M(3PPA)2Ni(CN)4 (M = Ni, Co, Cd, and Pd) have been prepared and their vibrational spectra are reported in the region of 4000–60 cm1. The vibrational bands arising from 3PPA ligand molecule, the polymeric sheet and metal–ligand bands of the compounds are assigned. The thermal behaviour of these complexes is also provided using the DTA and TGA along with the magnetic susceptibility data. The results indicate that the monodentate 3PPA ligand molecule bonds to the metal atom of jM–Ni(CN)4j1 polymeric layers and hence the compounds are similar in structure to Hofmann-type complexes. ß 2009 Elsevier B.V. All rights reserved.

Keywords: 3-Phenylpropylamine Hofmann-type complexes Infrared and Raman spectra TGA and DTA Nickel Cobalt Cadmium Palladium Tetracyanonickelate

1. Introduction Hofmann-type complexes are defined with the general formula of M(L)2Ni(CN)4 [1,2]. In this structure, the ligand molecule L can be N-donor [3,4], O-donor [5] or S-donor [6] molecules and M is a transition metal. During the last decade, complexes including the cyanometallate groups such as Hofmann-type complexes have been widely investigated due to their potential applications in hydrogen storage [7,8], as chemical sensors, non-linear optical devices, ion exchangers, molecular sieves [9–11] or magnetic materials [12,13]. 3-Phenylpropylamine (3PPA) metal derivatives have attracted special interest as an electrode material for the rechargeable lithium batteries [14], nanodevices [15] or ion exchangers [16] in the industrial applications. It is also used in medicinal applications as inhibitors [17], antimuscarinic drugs [18] or anticancer agents [19]. In our previous study, we reported the conformational analysis and vibrational spectroscopic investigation of the molecule and pointed out that TTG form among the other isomers can be more stable [20]. Also stability of this form was investigated

* Corresponding author. Tel.: +90 222 335 0580; fax: +90 222 320 4910. ¨ nal). E-mail address: [email protected] (A. U 0924-2031/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.vibspec.2009.08.003

by using theoretical and experimental NMR techniques in the five solvents [21]. In the present study, compounds prepared in the form of M(3PPA)2Ni(CN)4 (abbreviated hereafter as M–3PPA–Ni; M = Ni, Co, Cd and Pd) and their spectral properties in the infrared region of 4000–60 cm1 and in the Raman region of 3700–60 cm1 are reported. The thermal behaviour of the compounds is also provided via DTA and TGA methods. 2. Experimental part All the chemicals were obtained from Aldrich Europe and used without any purification. The compounds of M–3PPA–Ni (M = Ni, Co, Cd and Pd) were prepared at two stages. Firstly, KCN (4 mmol, 0.261 g) was dissolved in distilled water (10 mL) under stirring at room temperature, then a solution of NiCl26H2O (0.238 g, 1 mmol) prepared with distilled water (10 mL) was added dropwise to the dissolved KCN. Afterwards, a solution of metal (II) chloride, namely NiCl2 (0.130 g, 1 mmol), CoCl2 (0.131 g, 1 mmol), CdCl2 (0.184 g, 1 mmol) in distilled water (10 mL) and PdCl2 (0.178 g, 1 mmol) in ethanol (20 mL) was added slowly to this mixture and left for stirring around 1 h. The precipitates formed were filtered, washed with water, ethanol, ether and dried in the air at room temperature. In this way M(H2O)2Ni(CN)44H2O (M–Ni(CN)4) Hofmann–H2O-type hydrate products were obtained. Secondly,

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the distilled water (20 mL) was introduced to the M–Ni(CN)4 product [M = Ni (0.330 g, 1 mmol), M = Co (0.331 g, 1 mmol), M = Cd (0.384 g, 1 mmol), M = Pd (0.377 g, 1 mmol)] resulting to the finely divided suspension and around 2 mmol (0.3 mL) of the liquid ligand (3PPA) was added to this suspension under stirring. This mixture was stirred for 5 days. The obtained precipitates were filtered and washed as explained above, then dried in a desiccator containing P2O5. FT-IR (4000–400 cm1) spectra between KBr windows as Nujol or hexachloro-1,3-butadiene mulls and far-infrared (600– 60 cm1) spectra between polyethylene plates as Nujol mulls of the compounds were recorded via a Bruker Optics IFS66v/s FT-IR spectrometer with 2 cm1 resolution in vacuum. Raman spectra of the compounds were recorded using a Bruker Senterra Dispersive Raman microscope spectrometer with 532 or 633 nm excitations from a 3B diode laser having 3 cm1 resolution in the region of 3700 and 60 cm1. TGA and DTA curves of the compounds were recorded using the Setaram Setsys Evolution 1750 TG/DTA with around 20 mg of sample and a scanning rate of 10 8C min1 under nitrogen within the 30–1000 8C. Regarding magnetic susceptibility, the susceptibility measurement at room temperature was performed using a Sherwood Scientific Magway MSB MK1 model magnetic balance by the Gouy method using Hg[Co(SCN)4] as the calibrant. The compounds were also analyzed for C, H and N via a Fisons EA-108 elemental analyzer. The experimental data together with the calculated data based on the molecular weight are as follows (found %/calculated %):  Ni(C9H13N)2Ni(CN)4: 17.09).  Co(C9H13N)2Ni(CN)4: 17.08).  Cd(C9H13N)2Ni(CN)4: 15.40).  Pd(C9H13N)2Ni(CN)4: 15.57).

C (52.87/53.72), H (5.27/5.33), N (16.61/ C (52.10/53.69), H (5.28/5.33), N (16.31/ C (47.32/48.43), H (4.64/4.80), N (15.03/ C (48.81/48.97), H (4.72/4.86), N (15.19/

The experimental data are in agreement with the calculated amount indicating the formation of the Hofmann-type complexes. One also notices some paltry within analytical results that appear in the powder form of the Hofmann-type complexes [3]. 3. Theoretical part The geometry of the planar tetracyanonickelate ion [Ni(CN)4]2 with the D4h symmetry was optimized and its fundamental vibrational frequencies and corresponding normal modes characterized by potential energy distribution (P.E.D.) were calculated by density functional theory (DFT) using Becke’s three-parameter hybrid functional combined with the Lee–Yang– Parr correlation functional (B3LYP) and 6-311++G(d,p)/Lanl2dz basis sets. In order to fit the theoretical wavenumbers to the experimental values, two scaling procedures were used: scaling the harmonic wavenumbers by dual scale factors [22], or using several scale factors depending on the dominant term in each normal mode [23] (see Table 2). Thus, the calculated vibrational frequencies can be utilized to eliminate the uncertainties in the fundamental assignments of vibrational spectra [24]. The scaling procedure was not applied to the IR and Raman intensities. The calculated Raman activity data were converted to Raman intensities as described in the studies [20,25]. All the calculations were performed by using the Gaussian 03 program package [26] and the GaussView program was used for molecular visualization [27].

4. Results and discussions The FT-IR and far-infrared spectra of the M–3PPA–Ni (M = Ni, Co, Cd and Pd) compounds are given in Figs. 1 and 2. The Raman spectra of these compounds are given in Figs. 3 and 4. The spectral analyses of the each compound were performed by considering the free 3PPA molecule, polymeric sheet and metal– ligand modes individually, explained starting with the 3PPA ligand molecule. 4.1. 3PPA vibrations 3PPA has trans-trans-gauche (TTG) and trans-gauche-gauche (TGG) isomers. The TTG is the more stable form of the free 3PPA molecule [20]. The evaluation of the spectral features resulting from the ligand molecule in the compounds was based on the data of this form of the free 3PPA molecule. In Table 1, vibrational assignments and wavenumbers of the 3PPA molecule observed in the IR and Raman spectra of the compounds are given along with the free 3PPA molecule data that we reported previously. The studies of the Hofmann-type complexes point out that the spectral features on the coordination are the perturbeted vibrational frequencies of the ligand molecule resulting from the ligand molecule complexes to the metal atom [28–30]. As can be seen in Table 1, the frequency of the n(NH2) asymmetric band at 3372 cm1 are shifted to lower frequencies around 31–37 cm1. The shift for the n(NH2) symmetric band is around 7–16 cm1. Another noticeable shift takes place for the NH2 wagging that is around 47 cm1 for the compounds. The general shifting in the frequency of 3PPA modes with different metals of the complexes is in the order of Pd > Ni > Co > Cd, which is in agreement with the increasing order of the second ionization potential of these metals [31]. The frequency shifts to higher frequencies are also observed for the compounds. For example, n(CH2) asymmetric and symmetric band frequencies shifts around 7–9 cm1. The upward frequency shift for the n(CR–CH2) is around 8–12 cm1. The increases in frequencies results from the bonding of the metal atom to the ligand molecule making the difficult motion of these bands. Besides these frequency shifts, the small frequency shifts observed are from the environmental changes caused by the ligand molecule. The spectral features all together can indicate that the ligand molecule complexes to the metal atoms through N atom in the present compounds. 4.2. Polymeric sheet and metal–ligand vibrations The free tetracyanonickelate ion possesses ideally D4h symmetry with 21 fundamental vibrations that are 4 Eu, 2 A2u, 2 B2u, 1 Eg, 2 A1g, 1 A2g, 2B1g, 2 B2g. Among the modes, A2u and Eu are infrared active while A1g, B1g, B2g and Eg are Raman active. The A2g and B2u vibrations are inactive and B2g modes were not observed. To be able to assign all the bands of the tetracyanonickelate ion, density functional calculation was carried out and compared with the vibrational data of the tetracyanonickelate ion in Na2Ni(CN)4 and K2Ni(CN)4 complexes reported by McCullough et al. [33] and Kubas and Jones [34], see Table 2. The table indicates that scaled wavenumbers and assignments are well consistent with the experimental data except d(CNiC) vibration at 54 cm1. In Table 3, the vibrational wavenumbers of the polymeric sheet and metal–ligand vibrations of the present compounds are compared to the vibrational data of the relevant complexes and Hofmann-type clathrates of M(NH3)2Ni(CN)42Bz (M = Ni or Cd and Bz = Benzene) [35]. The vibrational spectroscopy is a valuable

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301

Fig. 1. The FT-IR spectra of Hofmann–3-PPA compounds in Nujol (*, **: in hexacholoro-1,3-butadiene): (a) Ni–3PPA–Ni, (b) Co–3PPA–Ni, (c) Cd–3PPA–Ni and (d) Pd–3PPA–Ni.

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Fig. 2. The far-infrared spectra of ligand molecule and Hofmann–3-PPA compounds in Nujol: (a) 3PPA, (b) Ni–3PPA–Ni, (c) Co–3PPA–Ni, (d) Cd–3PPA–Ni and (e) Pd–3PPA–Ni.

Table 1 The vibrational frequencies (cm1) of 3-PPA in the M–3PPA–Ni (M = Ni, Co, Cd and Pd) compounds. Assignmenta

3PPAa IR

n(NH2) as. n(NH2) s.

m w vw br vw m m

s w vs vs s m vs vs w w vw vw vw vw vw (3) m m m w sh m m s br vs vs vw m w w vw

IR

3377 3319 3203 3164 – – – 3054 3032 – 3002 2918 2855 1604 1584 1496 1439 – – 1340 1297 1203 1181 1157 1124 1075 – 1031 1002 920 843 806 749 – 621 577 492 453 422 349 283 229

3340 3280 – – 3103 3078 3057 – – 3024 3007 2924 2863 1594 1582 1493 1452 1381 1355 1333 1310 1215 1190 1156 1111 1076 1059 1024 987 906 839 758 722 692 – 588 – – – – – –

vw w vw vw

vs m br sh w m m m w vw br sh w

vw vw m vw br sh w (5s) vw m vs w vw m w w vw vw vw vw br vw br vw vw

s w

vw w vw

sb wb vsb sb s m vs vsb wb wb wb w w vw w vs m w m vs w m vs vs s s

Co–3PPA–Ni Raman

IR

3340 3281 – – – – 3067 3051 3032 – 3016 2925 2863 1592 1570 – – – – – – 1192 – 1161 1115 – – 1033 1004 – – 800 – – 626 – – – – 342 – 224

3338 3278 – – 3103 3078 3057 – – 3024 3004 2923 2863 1592 1581 1493 1452 1380 1356 1333 1310 1215 1190 1156 1105 1075 1059 1024 982 906 838 758 722 693 –– 567 – – – – – –

w s

m vs m w s m m w

m w w

m vs

m

w

w w

s w

vw w vw

sb wb vsb sb s m vs vsb wb wb vwb w w vw w s m w m vs w m vs vs s s

Cd–3PPA–Ni Raman

IR

3339 3278 – – – – 3064 3051 3031 – 3017 2925 2864 1590 1569 – – – – – – 1178 – 1146 1100 – – 1019 990 – – 785 – – 610 – – – – 318 – 232

3335 3274 – – 3102 3078 3056 – – 3020 3006 2927 2863 1591 1580 1492 1450 1385 1360 1334 1312 1216 1191 1154 1098 1072 1055 1022 974 908 837 757 722 694 – 560 – – – – – –

w s

m vs m w m m m w

m w w br

m vs

m

w

w w sh

s w

vw w vw

sb wb vsb sb s m vs vsb wb wb vwb w w vw w s m w m vs w m vs vs s s

Pd–3PPA–Ni Raman

IR

3332 3274 – – – – 3071 3050 3034 – 3024 2926 2865 1593 1570 – – – – – – 1179 – 1143 1087 – – 1018 988 – – 785 – – 610 – – – 301 – 210

3341 3283 – – 3103 3079 3059 – – 3023 3008 2923 2855 1594 1583 1494 1453 1378 1363 1333 1310 1212 1181 1156 1110 1074 1060 1024 986 910 840 757 722 702 – 587 – – – – – –

w s

m vs m w m m m w

m w w

m vs

m

w

w w

Raman s w

vw w vw

sb wb vsb sb s m vs vsb wb wb vwb w br w w w vs m w m vs w m vs vs s s

3341 3283 – – – – 3065 3048 3034 – Obscure 2926 2860 1594 1572 – – – – – – 1192 – 1163 1112 – – 1035 1006 – – 804 – – 625 – – – – 341 – 233

w m

m vs m

m m m w

m w w

m vs

m

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2NH2 def. 2nR(CC) NH2 def + nR(CC) nR(CH) nR(CH) nR(CH) nR(CH) nR(CH) 3R. breath. n(CH2) as. n(CH2) s. NH2 def. nR(CC) nR(CC) nR(CC), CH2 def CH2 wag. CH2 wag. nR(CC), CH2 tw bR(CH), CH2 tw n(CR–CH2) bR(CH) bR(CH) n(CCCN)c bR(CH) n(CCCN) n(CCCN) R. breath. gR(CH) gR(CH) NH2 wag. r(CH2) gR(CC) bR(CCC) n(skeletal) CCCN def. CCCN def. gR(CC) b(C–CH2) – g(C–CH2)

3372 3290 3190 – 3106 3085 3062 – – 3026 3002 2930 2856 1604 1584 1496 1453 1389 1352 1334 1310 1204 1179 1155 1124 1070 1046 1030 1002 909 873 805 746 699 621 573 495 459 422 – – –

Ni–3PPA–Ni Raman

w

w w

vs: very strong, s: strong, m: medium, w: weak, vw: very weak, br: broad, sh: shoulder. a Taken from Ref. [20]. b In hexachloro-1,3-butadiene. c Taken from Ref. [44]. This band was observed at n-propylamine molecule in solid phase.

303

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304

Table 2 Experimental and theoretical vibrational data of the tetracyanonickelate ion. Mode

21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Experimental Na2Ni(CN)4a 2149 2141 2132, 2128 543 g

P.E.D.f

B3LYP/6-311 + +g(d,p)//Lanl2dz Assignment

K2Ni(CN)4b

Assignment

n(C–N), A1g n(C–N), B1g n(C–N), Eu

2144c 2135c 2124c

n(CN), A1g n(CN), B1g n(CN), Eu

n(Ni–C), Eu

540

nas(Ni–C), Eu

442

p(NiCN), A2u

416

d(NiCN), Eu

415 405

ns(Ni–C), B1g ns(Ni–C), A1g

303

p(NiCN), Eg

a

b

488 448 (303) 433, 421

d(Ni–C–N), B2g p(Ni–C–N), A2u p(Ni–C–N), B2u d(Ni–C–N), Eu

405g 419g 325g 280g

n(Ni–C), B1g n(Ni–C), A1g d(Ni–C–NC–N), A2g p(Ni–C–N), Eg

(77) (91) (78)

p(C–Ni–C), A2u d(C–Ni–C), B2g d(C–Ni–C), Eu

108

d(CNiC), B2g

54h

d(C–Ni–C), B2u

54c

d(CNiC), B2u

n

d

2203 2191 2187 2187 518 518 489 456 401 395 395 366 364 340 306 306 120 119 116 116 54

n

e

n

2152 2141 2137 2137 497 497 470 438 385 379 379 351 349 326 294 294 115 114 111 111 52

f

2144 2132 2128 2128 560 560 492 445 391 409 409 396 394 342 299 299 121 110 107 107 53

Int. (IR)

Int. (Ra)

Sym.

Description (%)

0.0 0.0 141.3 141.3 0.2 0.2 0.0 0.3 0.0 48.7 48.7 0.0 0.0 0.0 0.0 0.0 34.2 0.0 2.7 2.7 0.0

1776.0 925.6 0.0 0.0 0.0 0.0 51.6 0.0 0.0 0.0 0.0 42.4 166.6 0.0 222.7 222.7 0.0 141.7 0.0 0.0 0.0

A1g B1g Eu Eu Eu Eu B2g A2u B2u Eu Eu B1g A1g A2g Eg Eg A2u B2g Eu Eu B2u

ns(CBBN) (100) nas(CBBN) (100) nas(CBBN) (97) nas(CBBN) (97) nas(Ni–C) (61), d(NiCN) (36) nas(Ni–C) (61), d(NiCN) (36) d(Ni–CN) (61); d(CNiC) (39) p(NiCN) (78); p(CNiC) (22) p(Ni–CN) (82); p(CNiC) (18) d(NiCN) (48); nas(Ni–C) (44) d(NiCN) (48); nas(Ni–C) (44) nas(Ni–C) (95) ns(Ni–C) (95) d(Ni–CN) (100) p(Ni–CN) (99) p(Ni–CN) (99) d(NiCN) (70); d(CNiC) (30) d(CNiC) (51); d(Ni–CN) (49) d(CNiC) (58); d(NiCN) (40) d(CNiC) (58); d(NiCN) (40) p(Ni–CN) (60); p(CNiC) (40)

n: bond stretching, d: in-plane angle bending, p: out-of-plane angle bending, as: asymmetric, s: symmetric. a

Taken from Ref. [33]: calculated values in parentheses were not observed. Taken from Ref. [34]. c Taken from Ref. [32]. d Calculated values (unscaled). e Wavenumbers scaled with dual scale factors: 0.960 (for wavenumbers under 1700 cm1) and 0.977 (for those over 1700 cm1). f Wavenumbers scaled using six scale factors depending on the dominant term in each normal mode (marked in bold): n(CBBN) = 0.9730, n(Ni–C) = 1.0828, d(NiCN) = 1.0053, d(CNiC) = 0.9233, p(NiCN) = 0.9758, p(CNiC) = 1.0000. g Obtained from summation bands. h Obtained from a difference band and a summation band. b

method for the characterization of supramolecular coordination polymers and especially for cyanometallate complexes. In this respect, it is a valuable tool for determining the orientation of the cyanide in an M–NC–Ni bridge. Typically, the original Ni–CN bond remains intact during reactions with other metals to produce linear bridges via the N atom and the CN of bridging cyanide is

largely depending on the original cyano stretching bands of Ni–CN. The terminal M–CN cyanometallate complexes exhibit distinctive peaks in the vibrational spectra between 2250 and 2000 cm1 [32]. The peaks in the region of 2180–2148 cm1 (IR) and 2195– 2148 cm1 (Ra) for the present compounds are associated with linear bridging cyano moieties. This points out that the polymeric

Table 3 The vibrational wavenumbers (cm1) of the polymeric sheet and metal-ligand vibrations in the compounds. Assignment

Na2Ni(CN)4a

K2Ni(CN)4b

M(NH3)2Ni(CN)4.2Bzd M = Ni

ns(CBBN), A1g nas(CBBN), B1g nas(CBBN), Eu nas(Ni–C), Eu d(Ni–CN), B2g p(NiCN), A2u d(NiCN), Eu ns(Ni–C), A1g nas(Ni–C), B1g d(Ni–CN), A2g p(Ni–CN), Eg d(CNiC), B2g d(CNiC), B2u nas(M–N)(3PPA), A2u nas(M–N)(CN)4, Eu ns(M–N) (3PPA), A1g/Eg d(NMN)(3PPA), A2u d(NMN)(CN)4, Eu d(NMN)(3PPA), A1u

2149 2141 2132, 2128 543 488 448 433 421 419 405 325 280 – 54

2144c 2135c 2124c 540 vw – 442 vw 416 s 405 m 415 w sh – 303 s 108 54c

545 – 460 436 412 470 498 – 333 110 – 372 270 250 238 204 181

w vw s sh m w m vs m m s w m m

M–3PPA–Ni

M = Cd

Ni

541 – 448 424 407 – – – 303 90 – 305 178 188 – 136 –

2175 2166 2167 554 – 463 439 436 – 480 – 324 105 – 375 266 253 224 210 –

vw sh s sh

m vs m m s m

Co vs m vs w m s s w w vs w s s m m

2168 2160 2160 553 – 462 437 – – 480 – 302 87 – 373 250 213 210 199 –

Cd vs m vs w m s

w w vs w m s m m

2160 2148 2148 557 – 464 428 423 – 481 – 291 73 – Obscure 199 165 148 127 ?109

Pd vs m vs w m s s w w vs

m s s s m

n: stretching, d: in-plane angle bending, p: out-of-plane angle bending, vs: very strong, s: strong, m: medium, w: weak, vw: very weak, sh: shoulder. a b c d

Taken from Ref. [33]. Taken from Ref. [34]. Taken from Ref. [32]. Taken from Ref. [35].

2195 2181 2180 555 – 463 440 423 – 486 – 320 102 – 373 267 248 240 219 –

vs m vs w m s s w w vs w s s m m

Compound

Temperature range (8C)

Ni(3-PPA)2Ni(CN)4

190–390

Co(3-PPA)2Ni(CN)4

405–545 165–400

Cd(3-PPA)2Ni(CN)4

410–585 170–380

Pd(3-PPA)2Ni(CN)4

440–695 695–790 160–395

415–565

DTAmax (8C)

220 295 346 510 175 232 302 534 176 292 667 755 174 242 333 532

(endo.) (endo.) (endo.) (exo.) (endo.) (endo.) (endo.) (exo.) (endo.) (endo.) (endo) (endo) (endo.) (endo.) (endo.) (exo.)

Removed group

Mass loss %

Total mass loss % Exp.

Residual product

Exp.

Calc.

Calc.

3-PPA

55.0

55.0

(CN)4 3-PPA

21.4 55.1

21.2 55.0

76.4

76.2

Ni–Ni Co–Ni(CN)4

(CN)4 3-PPA

22.0 50.5

21.2 49.6

77.1

76.2

Co–Ni Cd–Ni(CN)4

(CN)4 Cd 3-PPA

19.6 11.0 50.3

19.1 10.8 50.1

81.1

79.5

Cd–Ni Ni Pd–Ni(CN)4

(CN)4

20.5

19.3

70.8

69.4

Pd–Ni

Ni–Ni(CN)4

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Fig. 3. The Raman spectra of Hofmann–3-PPA compounds within the range of 2250–2100 cm1: (a) Ni–3PPA–Ni, (b) Co–3PPA–Ni, (c) Cd–3PPA–Ni and (d) Pd– 3PPA–Ni.

sheet structure of M–NC–Ni units is preserved in all of the M– 3PPA–Ni compounds. In the low wavenumber region, the vibrational frequencies of the IR active bands for the Ni(CN)4 group in polymeric sheet of the compounds are shifted upwards comparing the isolated unit. The upward frequency shifts are also observed for the Raman active bands. The frequency shifts are from the mechanical coupling of the internal modes of the Ni(CN)4 with metal since

Table 4 Thermoanalytical data for the four new Hofmann-type compounds.

305

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Fig. 4. The Raman spectra of Hofmann–3-PPA compounds: (a) Ni–3PPA–Ni, (b) Co–3PPA–Ni, (c) Cd–3PPA–Ni and (d) Pd–3PPA–Ni.

both ends of the CN group are bonded to the transition metal atoms. The observed frequency shifts are consistent with the studies regarding the Hofmann-type complexes [28–30]. It is also seen that the vibrational modes of the M–3PPA–Ni complexes are closer to those of Hofmann-type clathrates than that of the free Ni(CN)4 group. In addition, the comparison of the vibrational wavenumbers for the polymeric sheets of the isostructural compounds with ligand molecule also allows us a tentative assignment for metal–ligand n(M–N)(3PPA) symmetric, asymmetric stretching and d(NMN)(3PPA) bending vibrations. 5. Thermal analysis and magnetic susceptibility Thermal and elemental analyses for the present compounds are also considered besides to the vibrational spectroscopic studies that in turn provide the structural information on the compounds. The thermal analyses were performed by DTA and TGA methods in the temperature range of 30–1000 8C, the thermal curves for Ni– 3PPA–Ni and Cd–3PPA–Ni are given in Fig. 5. Thermo analytical data for the Hofmann-type compounds of 3-PPA are presented in Table 4. The thermal analysis curves for the M–3PPA–Ni (M = Ni, Co or Pd) compounds are similar and decomposition takes place in two stages: ligand molecule departure and release of the CN groups. For the Ni–3PPA–Ni, three partial endothermic peaks (DTGmax = 220, 295 and 346 8C) between 190 and 390 8C corresponds to decomposition of the ligand molecule. The mass loss calculations (found 55.0, calc. 55.0%) suggest the formation of Ni–Ni(CN)4 that is also seen from the IR spectra of intermediate residue at 400 8C. The intermediate forms in the decomposition of Hofmann-type complexes were reported

[36,37]. The exothermic peak (DTGmax = 510 8C) between 405 and 545 8C is for the metal cyanide decomposition (found 21.4, calc. 21.2%). The cyano group decomposition begins above 400 8C and the final product is found to be the metallic nickel after burning of organic residue. Thermal decomposition of the Co–3PPA–Ni in the temperature range of 165–400 8C (DTGmax = 175, 232 and 302 8C), degradation of the ligand molecule proceeds, followed by departure of the metal cyanides at 534 8C and stoichiometric mixture of metallic Co and Ni is left finally. The Pd–3PPA–Ni compound loses ligand molecules between 160 and 395 8C with the three partial endothermic at 174, 242 and 333 8C. The TG indicates mass loss (50.3%) corresponding to the formation of Pd–Ni(CN)4 (calc. 50.1%). The next mass loss between 415 and 565 8C is due to decomposition of metal cyanide (found 20.5, calc. 19.3%). The final residue product is the mixture of Pd and Ni. Among the compounds, the Cd–3PPA–Ni decomposition has three stages. The loss of the ligand molecule takes place between 170 and 380 8C at first. The following endothermic peak at 667 8C is for the decomposition of metal cyanide. The last endothermic peak (DTGmax = 755 8C) between 695 and 790 8C presents departure of Cd. The final residual product is found to be Ni (found 11.0, calc. 10.8%). The third stage is from the boiling point of the cadmium that is around 765–767 8C. The similar thermal behaviour was reported in the various studies [37–40]. For the magnetic susceptibilities of the complexes, the measurements were carried out using the Gouy balance method at room temperature. The effective magnetic moment values are 2.75 B.M. for Ni–3PPA–Ni, 4.70 B.M. for Co–3PPA–Ni, 2.74 B.M. for Pd–3PPA–Ni and Cd–3PPA–Ni complex is diamagnetic. The effective magnetic moment values are in

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Acknowledgements The authors would like to thank Hasan Bircan for the thermal analyses and to Cengiz Yenikaya for the magnetic susceptibility measurements. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] Fig. 5. The DTA and TGA curves of Hofmann–3-PPA compounds: (a) Ni–3PPA–Ni and (b) Cd–3PPA–Ni.

similar to Hofmann-type complexes and clathrates reported [3,41–43]. 6. Conclusion The vibrational spectroscopic study of the present compounds indicates that 3-phenylpropylamine acts as a monodentate ligand and bonds to the M in the M–3PPA–Ni complexes through the N atom. The spectral studies along with the structural agreement from the thermal and elemental analyses and the magnetic susceptibility data led us to conclude that the compounds are further example of the Hofmann-type complexes.

[26] [27] [28] [29] [30] [31] [32]

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