- Email: [email protected]
Raman spectroscopic study of two dimensional polymer compounds of 2-aminopyrimidine
Journal of Molecular Structure 744–747 (2005) 277–281 www.elsevier.com/locate/molstruc
Raman spectroscopic study of two dimensional polymer compounds of 2-aminopyrimidine Sevim Akyuza,*, Tanil Akyuzb b
a Faculty of Science, Department of Physics, Istanbul University, Vezneciler 34118, Istanbul, Turkey Science and Letters Faculty, Department of Physics, Istanbul Kultur University, 34510 Sirinevler, Istanbul, Turkey
Received 7 September 2004; accepted 11 October 2004 Available online 8 December 2004
Abstract The Raman spectra of the two dimensional layered polymer compounds, M(2APM)2M 0 (CN)4 {where MZMn or Cd; and M 0 ZNi or Pt; 2APMZ2-aminopyrimidine} are reported in the 70–4000 cmK1 region. Vibrational data suggests that compounds are similar in structure to C2 the Hofmann type two dimensional coordination polymer compounds, formed with M 0 ðCNÞK2 4 ions bridged by Mð2APMÞ2 cations. 2-Aminopyrimidine was coordinated to M(II) through one of the nitrogen atom of its heterocycle ring. Vibrational assignments are given for the bands arising from the tetracyanometallate layers and coordinated 2APM. q 2005 Elsevier B.V. All rights reserved. Keywords: Aminopyrimidine; Hofmann type complexes; Infrared and Raman spectra; Tetracyanonickelate; Tetracyanoplatinate; Transition metal
1. Introduction Pyrimidine is the parent heterocycle of very important group of compounds that have been extensively studied due to their occurrence in living systems. Aminopyrimidines are of great biological importance. NH2 groups substituted in pyrimidine rings are acidic components in hydrogen bonded interactions between pairs of nucleic bases responsible for formation of double helices in DNA and RNA [1,2]. Thus any information on their coordination properties is important as a means to understand the role of metal ions in biological systems. The well known Hofmann type two dimensional complexes, {M(L)2M 0 (CN)4}, are build by stacking the two dimensional extended metal (M 0 ) cyanide layers [3,4]. The two dimensional layer is constructed by the alternate linkage between square-planar M 0 (II) (M 0 ZNi, Pd or Pt) and octahedral M(II) (MZMn, Fe, Co, Ni, Cu, Zn or Cd) through the cyanide bridges. The octahedral coordination of M(II) is satisfied by four N-terminals of the cyano groups and two
nitrogen atoms of the two N-donor ligands (L) in trans configuration, protruding above and below the network [3,4]. We have previously reported the IR spectra of M(2APM)2 Ni(CN)4 complexes {where MZMn, Co, Ni or Cd} [5] and shown that the compounds are similar in structure to the Hofmann type two dimensional coordination polymer compounds, formed with NiðCNÞK2 ions bridged by 4 Mð2APMÞC2 2 cations. 2APM is coordinated to M(II) through one of the pyrimidine ring nitrogen atoms. We now report the Raman spectra of the M(2APM)2Ni(CN)4 {where MZMn or Cd; 2APMZ2-aminopyrimidine, abbreviated hereafter as M–Ni–2APM} for the first time in the 70–4000 cmK1 region. In order to compare the vibrational modes of the polymeric layers, the M(2APM)2Pt(CN)4 (MZCd or Mn) compounds were also prepared for the first time and their IR (400–4000 cmK1) and Raman data are reported. The aim of this study is to investigate the coordination ability of 2APM and to examine the ligand modes, particularly the vibrational modes arising metal–ligand bonds. 2. Experimental
* Corresponding author. Tel.: C90 212 455 5816; fax: C90 212 519 0834. E-mail address: [email protected] (S. Akyuz). 0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2004.10.048
All the chemicals used were reagent grade (Merck and Reidel) and used without further purification.
278
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
The complexes were prepared by adding slightly more than two moles of 2-aminopyrimidine and 1 mole of potassium tetracyanometallate aqueous solution to 1 mole of M(II) chloride solution using constant stirring. The C, H, N analyses were carried out for all the samples and the results were found to fit the proposed formulae well. The FTRaman spectra of the powdered samples were recorded on a Bruker RFS 100/S FT-Raman instrument using 1064 nm excitation from an Nd:YAG laser. The detector is a liquid nitrogen cooled Ge detector and 100 scans were accumulated. The IR spectra of nujol mulls or KBr discs were recorded on a Jasco 300E FT-IR spectrometer (2 cmK1 resolution).
3. Results and discussion The Raman spectra of the Mn–Ni–2APM and Cd–Ni– 2APM complexes are given in Fig. 1a and b, respectively. The IR and Raman spectra of Mn–Pt–2APM complex are given in Figs. 2 and 3, respectively. The vibrational spectra of the M–Pt–2APM complexes are very similar to those of M–Ni–2APM, indicating that they have analogous structures.
Fig. 1. FT-Raman spectra of Mn(2APM)2Ni(CN)4 (a) Cd(2APM)2Ni(CN)4 and (b) compounds.
Fig. 2. FT-IR spectrum of Mn(2APM)2Ni(CN)4 compound.
3.1. Vibrations of 2-aminopyrimidine 2-Aminopyrimidine has endo- and exo-cyclic nitrogen donors for coordination. The amino nitrogen atom is known to be more basic in comparison to the pyrimidine ring nitrogens [6]. However, in some 2-aminopyrimidine complexes the coordination of the 2-aminopyrimidine with the metal occurs through the endocyclic ring nitrogen [7–9], whereas in others the 2-aminopyrimidine coordinates to the metal through the amino nitrogen [6,10]. The vibrational wavenumbers of 2APM are tabulated in Table 1 in comparison with those of microcrystalline 2APM [5,11] and 2APM in a Ne matrix [12]. In our previous study based on IR spectroscopic results it was concluded that the 2APM molecule in Mn–Ni–2APM and Cd–Ni–2APM complexes, is coordinated to metal through one of the pyrimidine ring nitrogen atoms as a monodentate ligand [5] and the amino group nitrogen is not involved in the complex formation. Raman spectra support the previous findings. We clearly observed the symmetric stretching mode of NH2 group at 3378–3415 cmK1 in the Raman spectra of the compounds
Fig. 3. FT-Raman spectrum of Mn(2APM)2Ni(CN)4 compound.
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
279
Table 1 The wavenumbers (cmK1) of 2-aminopyrimidine in M–M 0 –2APM complexes Tentative assignmenta
2APM Ne matrix [12]
Solid [5]
Mn IR
Mn Ra
Cd IR
Cd Ra
Mn Ra
Cd Ra
na(NH2)
3585
3520s
–
3522s
–
–
–
ns(NH2)
3469
3348vs 3330vs 3244m 3168vs 3050vw 3025w 2960w 1648vs
3415vs
3418vs
3095 3022 3002 1623vs
3414m 3135m 3096m 3023s 3002m 1621s
3096w 3021w 3001w 1623vs
3415m – 3094w 3023s 2998m 1617s
3414vs – 3101m 3025s 3004m 1623s
3373vs – 3100m 3049w 3000w 1625s
1577s 1559vs 1479vs 1444s 1357m 1224m 1179m
1579m 1565vs 1483vs 1465s 1358s 1221m 1193m
1582s 1567sh 1478w 1463w 1355m – –
1578m 1564vs 1481vs 1463s 1357s 1224m 1191m
1582s – 1476w 1461w 1355s 1233vw 1193vw
1581s 1570w 1479m 1464m 1353s 1226vw 1193vw
1588s 1562 1474w 1457m 1357m – 1195vw
1130m 1078w 1039m
1130vw 1087w 1036w
1129vw 1083w 1032m
999m 988sp 869w 803vs 788m 726m 645m 602m 525s
984w
1129m 1085m – 1006m 983m
983m
1127m 1085s – 1005m 983w
1130s 1084s 1050vw 1007m –
1126w 1092s – 1004m 992vw
876w 799vs 764m – 651vs 584w 524w
875vs – – – 651m 597m 531?
874w 799vs – – 651s 576 526w
875s 811w 761vw 722vw 651m 597m 533m
877s 798vw 771m 721vw 653m 599m 531vw
877s – 780sh – 654m 599m –
405s
419msh
414s
421vs
414m
413m
412w
n(CH) n(CH) n(CH) d(NH2) nring nring nring nring (*) nring n(C–NH2) nring d (CH) Ring breath. NH2 twist.
1612 1606 1571 1560 1470 1454 1356 1219 1184sh 1177 1123
d ring
991
gCH gCH
872 805 786 732 642 593 521sh 517 407
gring NH2wag.(*) dring
M–Pt–2APM
M–Ni–2APM
Coordination sensitive bands are marked in bold. a Assignment is taken from Ref. [11] except where indicated with (*).
studied, higher than that of microcrystalline 2APM (3244 cmK1 IR). On the other hand, in the IR spectra of the M–Pt–2APM complexes, the na(NH2) and ns(NH2) modes are also found to have higher wavenumbers than those of microcrystalline 2APM (Table 1). Since it is well known that a coordinated amino group shows a negative shift around 100–150 cmK1, spectroscopic findings confirm that amino group nitrogen does not take part in coordination. Moreover, the n(C–NH2) mode of aniline and aniline derivatives shows a negative shift, DZ50–60 cmK1, upon coordination [13,14], but we do not observe such a drastic red shift of this mode in the M–M 0 –2APM complexes (Table 1) which is further evidence of non-coordination through the amino nitrogen. It must be noted that, according to X-ray results [15], in solid phase, amino group hydrogens of 2APM are involved in H-bonding interactions. The na(NH2) and ns(NH2) wavenumbers are obtained 3493–3522 and 3373–3415 cmK1 regions, respectively in the IR spectra of the M–M 0 –2APM complexes and the lowest in Cd–Ni– 2APM (3493 and 3373 cmK1) (Table 1 and Ref. [5]). The na(NH2) and ns(NH2) modes of 2APM were observed at
3540 and 3430 cmK1, respectively, in the IR spectra of 2APM in CCl4 solution [16]. Thus, although the na(NH2) and ns(NH2) modes of M–M 0 –2APM complexes are found to be higher in wavenumber than those of microcrystalline 2APM [5,11], they are slightly lower in value than those of 2APM in CCl4 solution [16] and in Ne matrix [12], indicating that the amino group hydrogens may be involved in a weak hydrogen bonding interaction, probably with guest water molecules, but H-bonding interaction must be weaker than in solid. It must be noted that samples are found to contain small amount of water as guest species (n(H2O) is observed around 3610 cmK1 as a weak intense band). As mentioned above, the lowest wavenumbers for amino group stretching modes were obtained for Cd–Ni–2APM complex, in which CN stretching modes (Eu, Ag and Bg) wavenumbers are also found to be the lowest as will be discussed below. In the case of Cd–Ni–2APM these relatively low wavenumbers (for NH2 str. and CN str.) may be due to inter molecular hydrogen bonding interaction between amino group hydrogens and pi electrons of CN group of the tetracyanonickelate layer. This result will be further
280
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
Table 2 Vibrational wavenumbers of tetracyanometallate group and metal-2APM vibrations Hofmann type clath.a M(NH)3 Ni(CN)4$2G
K2Pd(CN)4 [21]
K2Pt(CN)4 [18]
(2148–2156)c
2136b
539–552 451–455 426–433
541–545 450 421–428
462–477 312–322 –
445–455 303–305 90
485 425 383 2160b 2146b 424 296 94
2134 (2135,2124)d 505 (503)d (447, 443)d 300 (406)d
207–210
188–190
–
Assignment
K2Ni(CN)4 [21]
MZMn
MZCd
n(CN) Eu
2124b
(2148–2152)c
n(M 0 –CN) Eu p(M 0 CN) Au d(M 0 CN) Eu n(CN) Ag n(CN) Bg n(M 0 –CN) Ag p(M 0 CN) Eg d(CM’C) Bg
538 444 419
405 302 54b
n(M–L)2APM n(M–NC) d(LML)2APM a b c d e f
M(NH)3Pd(CN)4$ 2Bz [21] MZMn
465, 455 318 95
MZCd
2178e 495 434 412 2198e 2183e 482 317 –
491 428 408
483 304 80
198
181
M–Ni–2APM
M–Pt–2APM
Mn
Cd
Mn
Cd
2157f vs
2136f vs
2169 vs
2173 vs
553f w 456f sh 436f vs 2177 vs 2165s 452 w 318 m 75 vs
543f vw 442f sh 423f vs 2158 vs 2144s 451 m – –
507 m 457 s 446 m 2201 vs 2180s 472 m 335 m 71 vs
503 m 460 s 451 m 2203 vs 2182s 468 m 331 m 69 m
219s 198 w 104 vs
190s 144 w 95 vs
213s 193 w 103 vs
198s 166 w 94 vs
Hofmann type clathrates M(NH)3Ni(CN)4$2G where G is the guest molecule (benzene, aniline or thiophene); taken from Ref. [21] except where indicated. Taken from Ref. [18]. Taken from Ref. [23]. Our values. For MZNi, taken from Ref. [22]. Taken from Ref. [5].
discussed below. The absence of large systematic shifts to lower wavenumbers for na(NH2), ns(NH2) and n(C–NH2) vibrational bands in the IR and Raman spectra of the complexes studied, implies that there is no interaction between the amino group nitrogen and the metal (MZMn or Cd). In the case of pyridine–metal complexes, a shift to higher wavenumber in the ring breathing mode is used as a guide to metal coordination [17–18]. The increase in value in certain ring modes was found to be both due to coupling with M–N (pyridine) bond vibrations and alterations of the ring force field [17,19]. We clearly observed upward frequency shift on the ring breathing mode of 2APM and the other coordination sensitive modes, which were marked in bold in Table 1. Therefore, based on the spectral results, it is concluded that the ring nitrogen and not the amino nitrogen is involved in complex formation. 3.2. Vibrations of the polymeric sheet The polymeric sheet structure of M–Ni–2APM and M–Pt–2APM compounds consists of a network of either Ni(CN)4 or Pt(CN)4 groups. If a local C4h environment for the Ni or Pd atom is assumed, one IR active (Eu) and two Raman active (Ag and Bg) CN stretching vibrations are expected. This is what we observed in the vibrational spectra of the M–Pt–2APM compounds. Relative to the high wavenumber region, the assignment for below the 300 cmK1 region is more complex because of the lack of the far IR and Raman data. But we took the advantage of studying isostructural compounds.
The assignment reported here based on the band shifts introduced by Pt substitution instead of Ni, in tetracyanometallate layers and on the comparison with the Raman spectra of Hofmann type clathrates [20,21] and tetracyanometallate complexes [18] where available. The wavenumbers of the tetracyanometallate group and those of metal-2APM vibrations {n(M–L) 2APM and d(LML)2APM} are given in Table 2. In the case of Cd– Ni–2APM, the CN stretching (Ag, Bg and Eu) wavenumbers are lower than those of Mn–Ni–2APM. A possible reason for the lower wavenumbers in the Cd–Ni–2APM complex is the presence of hydrogen bonding between NH2 group of 2APM and the pi electrons of the cyanide groups of the tetracyanide sheet leading a reduction in the force constant of the ChN bond. As discussed previous section the amino group stretching wavenumbers of the Cd–Ni– 2APM complex was found to be the lowest among the M–M 0 –2APM complexes studied. According to the X-ray crystallographic studies on Hofmann type compounds, the unit cell dimensions increase with the increasing ionic radius of the octahedral metal (M), where square-planar metal (M 0 ) is the same [3]. Therefore probably unit cell dimensions of the Cd–Ni–2APM complex are more suitable than the others for such interaction. In the case of M–Pt–2APM complexes, Pt substitution result in upward shift in the CN stretching bands. Similar shifts were also observed in Ni(NH3)2Pd(CN)4$2C6H6 clathrate [22] and M(aniline)Pt(CN)4 complexes [13], and explained by the difference in the electronegativity between Ni and Pd or Pt, the oxidation state being the same for both metals [13,18,22].
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
4. Conclusion IR and Raman spectroscopy provides a powerful means to assess the effects of coordination and the coordination mode on 2APM. From these spectroscopic studies it is concluded that 2APM acts as a monodentate ligand and bonding through the endocyclic nitrogen in the two new complexes prepared (Mn–Pt–2APM and Cd–Pt–2APM) and Raman results confirmed previous predicted structure for M–Ni–2APM complexes. Comparison of the vibrational wavenumbers of tetracyanametallate sheet of the isostructural compounds lead us to express a tentative assignment for n(M–N)2APM, n(M–NC) and d(NMN)2APM vibrations. However some more data for the low wavenumber region of the tetracyanometallate compounds are needed to be sure in the assignment. Our future study will be devoted on this subject.
Acknowledgements This work was supported by the Research fund of the University of Istanbul. Project number UDP-347/15072004. The authors wish to thank Professor Mehmet Somer for Raman measurements in Koc University, Istanbul, Turkey.
References [1] R.K. Murray, D.K. Granner, P.A. Mayes, V.W. Rodwell, Harper’s Biochemistry, 22th ed., Prentice Hall, London, 1990. [2] S.N. Pandeya, D. Sriram, G. Nath, E. De Clercq, Il Farmaco 54 (1999) 624.
281
[3] T. Iwamoto, in J.L. Atwood, J.E.D. Davies, D.D. MacNicol (Eds.), Inclusion Compounds vol. 1, Academic Press, London 1984, Chapter 2, p. 29; vol. 5, Oxford University Press, 1991, Chapter 6, p. 177. [4] T. Iwamoto, J. Incls. Phenom. 24 (1996) 61. [5] S. Akyuz, J. Supramol. Chem. 2 (2002) 401. [6] T.W. Stringfield, R.E. Shepherd, Inorg. Chem Commun. 4 (2001) 760. [7] G.A. Albada, M.E. Quiroz-Castro, I. Mutikainen, U. Turpeinen, J. Reedijk, Inorg. Chim. Acta 298 (2000) 221. [8] G.A. Albada, I. Mutikainen, J.J. Smeets, A.L. Spek, U. Turpeinen, J. Reedijk, Inorg. Chim. Acta 327 (2002) 134. [9] D. Kovala-Demertzi, N. Kourkoumelis, P. Tavridou, A. Moukarika, P.D. Akrivos, U. Russo, Spectrochim. Acta 54A (1998) 1801. [10] J.G. Contreras, G.V. Seguel, J.A. Gnecco, Spectrochim. Acta 48A (1992) 525. [11] E. Spinner, J. Chem. Soc. 1962; 3119. [12] W.J. McCarty, L. Lapinski, M.J. Nowak, L. Adamowics, J. Chem. Phys. 108 (1998) 10116. [13] S. Akyuz, J. Mol. Struct. 68 (1980) 41. [14] E. Akalin, S. Akyuz, J. Mol. Struct. 463–464 (2001) 579. [15] J. Scheinbeim, E. Schempp, Acta Crystallogr. 32B (1976) 607. [16] V.E. Borisenko, S.A. Krekov, G.A. Guzemin, A. Koll, J. Mol. Struct. 646 (2003) 125. [17] S. Suzuki, W.J. Orville-Thomas, J. Mol. Struct. 37 (1977) 321. [18] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, fourth ed., Wiley, New York, 1986. p. 279. [19] M. Bakiler, I.V. Maslov, S. Akyuz, J. Mol. Struct. 476 (1999) 21. [20] L. Andreeva, B. Minceva-Sukarova, J. Mol. Struct. 408–409 (1997) 435. [21] B. Minceva-Sukarova, L. Andreeva, S. Akyuz, C.A. Koh, Proceedings of the Sixth International Conference on Fundamental and Applied Aspects of Physical Chemistry, September 2002, Belgrade, Yugoslavia, vol. I, 2002, p. 66. [22] S. Suzuki, W.J. Orville-Thomas, A. Sopkava, J. Skorsepa, J. Mol. Struct. 54 (1979) 1. [23] S. Akyuz, A.B. Dempster, R.L. Morehouse, Spectrochim. Acta 30A (1974) 1989.
Raman spectroscopic study of two dimensional polymer compounds of 2-aminopyrimidine Sevim Akyuza,*, Tanil Akyuzb b
a Faculty of Science, Department of Physics, Istanbul University, Vezneciler 34118, Istanbul, Turkey Science and Letters Faculty, Department of Physics, Istanbul Kultur University, 34510 Sirinevler, Istanbul, Turkey
Received 7 September 2004; accepted 11 October 2004 Available online 8 December 2004
Abstract The Raman spectra of the two dimensional layered polymer compounds, M(2APM)2M 0 (CN)4 {where MZMn or Cd; and M 0 ZNi or Pt; 2APMZ2-aminopyrimidine} are reported in the 70–4000 cmK1 region. Vibrational data suggests that compounds are similar in structure to C2 the Hofmann type two dimensional coordination polymer compounds, formed with M 0 ðCNÞK2 4 ions bridged by Mð2APMÞ2 cations. 2-Aminopyrimidine was coordinated to M(II) through one of the nitrogen atom of its heterocycle ring. Vibrational assignments are given for the bands arising from the tetracyanometallate layers and coordinated 2APM. q 2005 Elsevier B.V. All rights reserved. Keywords: Aminopyrimidine; Hofmann type complexes; Infrared and Raman spectra; Tetracyanonickelate; Tetracyanoplatinate; Transition metal
1. Introduction Pyrimidine is the parent heterocycle of very important group of compounds that have been extensively studied due to their occurrence in living systems. Aminopyrimidines are of great biological importance. NH2 groups substituted in pyrimidine rings are acidic components in hydrogen bonded interactions between pairs of nucleic bases responsible for formation of double helices in DNA and RNA [1,2]. Thus any information on their coordination properties is important as a means to understand the role of metal ions in biological systems. The well known Hofmann type two dimensional complexes, {M(L)2M 0 (CN)4}, are build by stacking the two dimensional extended metal (M 0 ) cyanide layers [3,4]. The two dimensional layer is constructed by the alternate linkage between square-planar M 0 (II) (M 0 ZNi, Pd or Pt) and octahedral M(II) (MZMn, Fe, Co, Ni, Cu, Zn or Cd) through the cyanide bridges. The octahedral coordination of M(II) is satisfied by four N-terminals of the cyano groups and two
nitrogen atoms of the two N-donor ligands (L) in trans configuration, protruding above and below the network [3,4]. We have previously reported the IR spectra of M(2APM)2 Ni(CN)4 complexes {where MZMn, Co, Ni or Cd} [5] and shown that the compounds are similar in structure to the Hofmann type two dimensional coordination polymer compounds, formed with NiðCNÞK2 ions bridged by 4 Mð2APMÞC2 2 cations. 2APM is coordinated to M(II) through one of the pyrimidine ring nitrogen atoms. We now report the Raman spectra of the M(2APM)2Ni(CN)4 {where MZMn or Cd; 2APMZ2-aminopyrimidine, abbreviated hereafter as M–Ni–2APM} for the first time in the 70–4000 cmK1 region. In order to compare the vibrational modes of the polymeric layers, the M(2APM)2Pt(CN)4 (MZCd or Mn) compounds were also prepared for the first time and their IR (400–4000 cmK1) and Raman data are reported. The aim of this study is to investigate the coordination ability of 2APM and to examine the ligand modes, particularly the vibrational modes arising metal–ligand bonds. 2. Experimental
* Corresponding author. Tel.: C90 212 455 5816; fax: C90 212 519 0834. E-mail address: [email protected] (S. Akyuz). 0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2004.10.048
All the chemicals used were reagent grade (Merck and Reidel) and used without further purification.
278
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
The complexes were prepared by adding slightly more than two moles of 2-aminopyrimidine and 1 mole of potassium tetracyanometallate aqueous solution to 1 mole of M(II) chloride solution using constant stirring. The C, H, N analyses were carried out for all the samples and the results were found to fit the proposed formulae well. The FTRaman spectra of the powdered samples were recorded on a Bruker RFS 100/S FT-Raman instrument using 1064 nm excitation from an Nd:YAG laser. The detector is a liquid nitrogen cooled Ge detector and 100 scans were accumulated. The IR spectra of nujol mulls or KBr discs were recorded on a Jasco 300E FT-IR spectrometer (2 cmK1 resolution).
3. Results and discussion The Raman spectra of the Mn–Ni–2APM and Cd–Ni– 2APM complexes are given in Fig. 1a and b, respectively. The IR and Raman spectra of Mn–Pt–2APM complex are given in Figs. 2 and 3, respectively. The vibrational spectra of the M–Pt–2APM complexes are very similar to those of M–Ni–2APM, indicating that they have analogous structures.
Fig. 1. FT-Raman spectra of Mn(2APM)2Ni(CN)4 (a) Cd(2APM)2Ni(CN)4 and (b) compounds.
Fig. 2. FT-IR spectrum of Mn(2APM)2Ni(CN)4 compound.
3.1. Vibrations of 2-aminopyrimidine 2-Aminopyrimidine has endo- and exo-cyclic nitrogen donors for coordination. The amino nitrogen atom is known to be more basic in comparison to the pyrimidine ring nitrogens [6]. However, in some 2-aminopyrimidine complexes the coordination of the 2-aminopyrimidine with the metal occurs through the endocyclic ring nitrogen [7–9], whereas in others the 2-aminopyrimidine coordinates to the metal through the amino nitrogen [6,10]. The vibrational wavenumbers of 2APM are tabulated in Table 1 in comparison with those of microcrystalline 2APM [5,11] and 2APM in a Ne matrix [12]. In our previous study based on IR spectroscopic results it was concluded that the 2APM molecule in Mn–Ni–2APM and Cd–Ni–2APM complexes, is coordinated to metal through one of the pyrimidine ring nitrogen atoms as a monodentate ligand [5] and the amino group nitrogen is not involved in the complex formation. Raman spectra support the previous findings. We clearly observed the symmetric stretching mode of NH2 group at 3378–3415 cmK1 in the Raman spectra of the compounds
Fig. 3. FT-Raman spectrum of Mn(2APM)2Ni(CN)4 compound.
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
279
Table 1 The wavenumbers (cmK1) of 2-aminopyrimidine in M–M 0 –2APM complexes Tentative assignmenta
2APM Ne matrix [12]
Solid [5]
Mn IR
Mn Ra
Cd IR
Cd Ra
Mn Ra
Cd Ra
na(NH2)
3585
3520s
–
3522s
–
–
–
ns(NH2)
3469
3348vs 3330vs 3244m 3168vs 3050vw 3025w 2960w 1648vs
3415vs
3418vs
3095 3022 3002 1623vs
3414m 3135m 3096m 3023s 3002m 1621s
3096w 3021w 3001w 1623vs
3415m – 3094w 3023s 2998m 1617s
3414vs – 3101m 3025s 3004m 1623s
3373vs – 3100m 3049w 3000w 1625s
1577s 1559vs 1479vs 1444s 1357m 1224m 1179m
1579m 1565vs 1483vs 1465s 1358s 1221m 1193m
1582s 1567sh 1478w 1463w 1355m – –
1578m 1564vs 1481vs 1463s 1357s 1224m 1191m
1582s – 1476w 1461w 1355s 1233vw 1193vw
1581s 1570w 1479m 1464m 1353s 1226vw 1193vw
1588s 1562 1474w 1457m 1357m – 1195vw
1130m 1078w 1039m
1130vw 1087w 1036w
1129vw 1083w 1032m
999m 988sp 869w 803vs 788m 726m 645m 602m 525s
984w
1129m 1085m – 1006m 983m
983m
1127m 1085s – 1005m 983w
1130s 1084s 1050vw 1007m –
1126w 1092s – 1004m 992vw
876w 799vs 764m – 651vs 584w 524w
875vs – – – 651m 597m 531?
874w 799vs – – 651s 576 526w
875s 811w 761vw 722vw 651m 597m 533m
877s 798vw 771m 721vw 653m 599m 531vw
877s – 780sh – 654m 599m –
405s
419msh
414s
421vs
414m
413m
412w
n(CH) n(CH) n(CH) d(NH2) nring nring nring nring (*) nring n(C–NH2) nring d (CH) Ring breath. NH2 twist.
1612 1606 1571 1560 1470 1454 1356 1219 1184sh 1177 1123
d ring
991
gCH gCH
872 805 786 732 642 593 521sh 517 407
gring NH2wag.(*) dring
M–Pt–2APM
M–Ni–2APM
Coordination sensitive bands are marked in bold. a Assignment is taken from Ref. [11] except where indicated with (*).
studied, higher than that of microcrystalline 2APM (3244 cmK1 IR). On the other hand, in the IR spectra of the M–Pt–2APM complexes, the na(NH2) and ns(NH2) modes are also found to have higher wavenumbers than those of microcrystalline 2APM (Table 1). Since it is well known that a coordinated amino group shows a negative shift around 100–150 cmK1, spectroscopic findings confirm that amino group nitrogen does not take part in coordination. Moreover, the n(C–NH2) mode of aniline and aniline derivatives shows a negative shift, DZ50–60 cmK1, upon coordination [13,14], but we do not observe such a drastic red shift of this mode in the M–M 0 –2APM complexes (Table 1) which is further evidence of non-coordination through the amino nitrogen. It must be noted that, according to X-ray results [15], in solid phase, amino group hydrogens of 2APM are involved in H-bonding interactions. The na(NH2) and ns(NH2) wavenumbers are obtained 3493–3522 and 3373–3415 cmK1 regions, respectively in the IR spectra of the M–M 0 –2APM complexes and the lowest in Cd–Ni– 2APM (3493 and 3373 cmK1) (Table 1 and Ref. [5]). The na(NH2) and ns(NH2) modes of 2APM were observed at
3540 and 3430 cmK1, respectively, in the IR spectra of 2APM in CCl4 solution [16]. Thus, although the na(NH2) and ns(NH2) modes of M–M 0 –2APM complexes are found to be higher in wavenumber than those of microcrystalline 2APM [5,11], they are slightly lower in value than those of 2APM in CCl4 solution [16] and in Ne matrix [12], indicating that the amino group hydrogens may be involved in a weak hydrogen bonding interaction, probably with guest water molecules, but H-bonding interaction must be weaker than in solid. It must be noted that samples are found to contain small amount of water as guest species (n(H2O) is observed around 3610 cmK1 as a weak intense band). As mentioned above, the lowest wavenumbers for amino group stretching modes were obtained for Cd–Ni–2APM complex, in which CN stretching modes (Eu, Ag and Bg) wavenumbers are also found to be the lowest as will be discussed below. In the case of Cd–Ni–2APM these relatively low wavenumbers (for NH2 str. and CN str.) may be due to inter molecular hydrogen bonding interaction between amino group hydrogens and pi electrons of CN group of the tetracyanonickelate layer. This result will be further
280
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
Table 2 Vibrational wavenumbers of tetracyanometallate group and metal-2APM vibrations Hofmann type clath.a M(NH)3 Ni(CN)4$2G
K2Pd(CN)4 [21]
K2Pt(CN)4 [18]
(2148–2156)c
2136b
539–552 451–455 426–433
541–545 450 421–428
462–477 312–322 –
445–455 303–305 90
485 425 383 2160b 2146b 424 296 94
2134 (2135,2124)d 505 (503)d (447, 443)d 300 (406)d
207–210
188–190
–
Assignment
K2Ni(CN)4 [21]
MZMn
MZCd
n(CN) Eu
2124b
(2148–2152)c
n(M 0 –CN) Eu p(M 0 CN) Au d(M 0 CN) Eu n(CN) Ag n(CN) Bg n(M 0 –CN) Ag p(M 0 CN) Eg d(CM’C) Bg
538 444 419
405 302 54b
n(M–L)2APM n(M–NC) d(LML)2APM a b c d e f
M(NH)3Pd(CN)4$ 2Bz [21] MZMn
465, 455 318 95
MZCd
2178e 495 434 412 2198e 2183e 482 317 –
491 428 408
483 304 80
198
181
M–Ni–2APM
M–Pt–2APM
Mn
Cd
Mn
Cd
2157f vs
2136f vs
2169 vs
2173 vs
553f w 456f sh 436f vs 2177 vs 2165s 452 w 318 m 75 vs
543f vw 442f sh 423f vs 2158 vs 2144s 451 m – –
507 m 457 s 446 m 2201 vs 2180s 472 m 335 m 71 vs
503 m 460 s 451 m 2203 vs 2182s 468 m 331 m 69 m
219s 198 w 104 vs
190s 144 w 95 vs
213s 193 w 103 vs
198s 166 w 94 vs
Hofmann type clathrates M(NH)3Ni(CN)4$2G where G is the guest molecule (benzene, aniline or thiophene); taken from Ref. [21] except where indicated. Taken from Ref. [18]. Taken from Ref. [23]. Our values. For MZNi, taken from Ref. [22]. Taken from Ref. [5].
discussed below. The absence of large systematic shifts to lower wavenumbers for na(NH2), ns(NH2) and n(C–NH2) vibrational bands in the IR and Raman spectra of the complexes studied, implies that there is no interaction between the amino group nitrogen and the metal (MZMn or Cd). In the case of pyridine–metal complexes, a shift to higher wavenumber in the ring breathing mode is used as a guide to metal coordination [17–18]. The increase in value in certain ring modes was found to be both due to coupling with M–N (pyridine) bond vibrations and alterations of the ring force field [17,19]. We clearly observed upward frequency shift on the ring breathing mode of 2APM and the other coordination sensitive modes, which were marked in bold in Table 1. Therefore, based on the spectral results, it is concluded that the ring nitrogen and not the amino nitrogen is involved in complex formation. 3.2. Vibrations of the polymeric sheet The polymeric sheet structure of M–Ni–2APM and M–Pt–2APM compounds consists of a network of either Ni(CN)4 or Pt(CN)4 groups. If a local C4h environment for the Ni or Pd atom is assumed, one IR active (Eu) and two Raman active (Ag and Bg) CN stretching vibrations are expected. This is what we observed in the vibrational spectra of the M–Pt–2APM compounds. Relative to the high wavenumber region, the assignment for below the 300 cmK1 region is more complex because of the lack of the far IR and Raman data. But we took the advantage of studying isostructural compounds.
The assignment reported here based on the band shifts introduced by Pt substitution instead of Ni, in tetracyanometallate layers and on the comparison with the Raman spectra of Hofmann type clathrates [20,21] and tetracyanometallate complexes [18] where available. The wavenumbers of the tetracyanometallate group and those of metal-2APM vibrations {n(M–L) 2APM and d(LML)2APM} are given in Table 2. In the case of Cd– Ni–2APM, the CN stretching (Ag, Bg and Eu) wavenumbers are lower than those of Mn–Ni–2APM. A possible reason for the lower wavenumbers in the Cd–Ni–2APM complex is the presence of hydrogen bonding between NH2 group of 2APM and the pi electrons of the cyanide groups of the tetracyanide sheet leading a reduction in the force constant of the ChN bond. As discussed previous section the amino group stretching wavenumbers of the Cd–Ni– 2APM complex was found to be the lowest among the M–M 0 –2APM complexes studied. According to the X-ray crystallographic studies on Hofmann type compounds, the unit cell dimensions increase with the increasing ionic radius of the octahedral metal (M), where square-planar metal (M 0 ) is the same [3]. Therefore probably unit cell dimensions of the Cd–Ni–2APM complex are more suitable than the others for such interaction. In the case of M–Pt–2APM complexes, Pt substitution result in upward shift in the CN stretching bands. Similar shifts were also observed in Ni(NH3)2Pd(CN)4$2C6H6 clathrate [22] and M(aniline)Pt(CN)4 complexes [13], and explained by the difference in the electronegativity between Ni and Pd or Pt, the oxidation state being the same for both metals [13,18,22].
S. Akyuz, T. Akyuz / Journal of Molecular Structure 744–747 (2005) 277–281
4. Conclusion IR and Raman spectroscopy provides a powerful means to assess the effects of coordination and the coordination mode on 2APM. From these spectroscopic studies it is concluded that 2APM acts as a monodentate ligand and bonding through the endocyclic nitrogen in the two new complexes prepared (Mn–Pt–2APM and Cd–Pt–2APM) and Raman results confirmed previous predicted structure for M–Ni–2APM complexes. Comparison of the vibrational wavenumbers of tetracyanametallate sheet of the isostructural compounds lead us to express a tentative assignment for n(M–N)2APM, n(M–NC) and d(NMN)2APM vibrations. However some more data for the low wavenumber region of the tetracyanometallate compounds are needed to be sure in the assignment. Our future study will be devoted on this subject.
Acknowledgements This work was supported by the Research fund of the University of Istanbul. Project number UDP-347/15072004. The authors wish to thank Professor Mehmet Somer for Raman measurements in Koc University, Istanbul, Turkey.
References [1] R.K. Murray, D.K. Granner, P.A. Mayes, V.W. Rodwell, Harper’s Biochemistry, 22th ed., Prentice Hall, London, 1990. [2] S.N. Pandeya, D. Sriram, G. Nath, E. De Clercq, Il Farmaco 54 (1999) 624.
281
[3] T. Iwamoto, in J.L. Atwood, J.E.D. Davies, D.D. MacNicol (Eds.), Inclusion Compounds vol. 1, Academic Press, London 1984, Chapter 2, p. 29; vol. 5, Oxford University Press, 1991, Chapter 6, p. 177. [4] T. Iwamoto, J. Incls. Phenom. 24 (1996) 61. [5] S. Akyuz, J. Supramol. Chem. 2 (2002) 401. [6] T.W. Stringfield, R.E. Shepherd, Inorg. Chem Commun. 4 (2001) 760. [7] G.A. Albada, M.E. Quiroz-Castro, I. Mutikainen, U. Turpeinen, J. Reedijk, Inorg. Chim. Acta 298 (2000) 221. [8] G.A. Albada, I. Mutikainen, J.J. Smeets, A.L. Spek, U. Turpeinen, J. Reedijk, Inorg. Chim. Acta 327 (2002) 134. [9] D. Kovala-Demertzi, N. Kourkoumelis, P. Tavridou, A. Moukarika, P.D. Akrivos, U. Russo, Spectrochim. Acta 54A (1998) 1801. [10] J.G. Contreras, G.V. Seguel, J.A. Gnecco, Spectrochim. Acta 48A (1992) 525. [11] E. Spinner, J. Chem. Soc. 1962; 3119. [12] W.J. McCarty, L. Lapinski, M.J. Nowak, L. Adamowics, J. Chem. Phys. 108 (1998) 10116. [13] S. Akyuz, J. Mol. Struct. 68 (1980) 41. [14] E. Akalin, S. Akyuz, J. Mol. Struct. 463–464 (2001) 579. [15] J. Scheinbeim, E. Schempp, Acta Crystallogr. 32B (1976) 607. [16] V.E. Borisenko, S.A. Krekov, G.A. Guzemin, A. Koll, J. Mol. Struct. 646 (2003) 125. [17] S. Suzuki, W.J. Orville-Thomas, J. Mol. Struct. 37 (1977) 321. [18] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, fourth ed., Wiley, New York, 1986. p. 279. [19] M. Bakiler, I.V. Maslov, S. Akyuz, J. Mol. Struct. 476 (1999) 21. [20] L. Andreeva, B. Minceva-Sukarova, J. Mol. Struct. 408–409 (1997) 435. [21] B. Minceva-Sukarova, L. Andreeva, S. Akyuz, C.A. Koh, Proceedings of the Sixth International Conference on Fundamental and Applied Aspects of Physical Chemistry, September 2002, Belgrade, Yugoslavia, vol. I, 2002, p. 66. [22] S. Suzuki, W.J. Orville-Thomas, A. Sopkava, J. Skorsepa, J. Mol. Struct. 54 (1979) 1. [23] S. Akyuz, A.B. Dempster, R.L. Morehouse, Spectrochim. Acta 30A (1974) 1989.