on

2-

erab

Lan

en Un

ca An

ze 17/A, 43100 Parma, Italy

accepted 20 September 2004

ne 28

O)2]$ligan

in the triclinic space group PK1, are isostructural, and their solid structures are stabilized by hydrogen bonding and pp interactionsbetween aminopyrimidine rings. The compounds exhibit solvatochromism as evidenced by a UV/Vis study in different solvents.

chromotropic and exhibit color change when exposed to

Journal of Molecular Structu0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.q 2004 Elsevier B.V. All rights reserved.

Keywords: Copper; Solvatochromism; 2-Aminopyrimidine; Thiocyanate

1. Introduction

Structure and magnetic studies of metal complexes with

2-aminopyrimidine (abbreviated as ampym) are of con-

siderable interest due to the coordination diversity exhibited

by the ligand and metal ions [1,2]. With Cu(II), quite a large

number of different compounds have been reported and the

structures often depend on the nature of the anion and the

synthetic method [2,3]. With Ni(II) and Co(II) and ampym

as a ligand only a few complexes have been determined by

X-ray diffraction methods [4,5].

The investigation of the solvatochromic behavior [6] of

mixed-ligand metal complexes has been of importance,

because it provides a quantitative approach to recognize the

solvent behavior and the role of the solvent in physico-

chemical studies [7]; moreover, it is very helpful for

developing environmental sensor materials, which are

In the present paper, the synthesis and characterization of

two mononuclear isostructural thiocyanato compounds with

the general formula [M(ampym)2(SCN)2(H2O)2]$2H2O(MZNi(II), Co(II)) will be reported. In addition, thesolvatochromism of both compounds has been investigated

by UV/vis in different solvents.

2. Experimental section

2.1. General remarks and physical measurements

All starting reagents and solvents were purchased from

commercial sources and used as received. C, H, N analyses

were performed on a PerkinElmer 2400 series II analyzer.

Infrared spectra were recorded on a PerkinElmer Paragon

1000 spectrophotometer equipped with a Golden Gate ATRSynthesis, structural characterisati

and a Co(II) compound with

Yufei Songa, Chiara MassAnna Maria Manotti

aGorlaeus Laboratories, Leiden Institute of Chemistry, LeidbDipartimento di Chimica Generale ed Inorganica, Chimi

Parco Area delle Scien

Received 7 July 2004;

Available onli

Abstract

Two mononuclear complexes of formula [M(ampym)2(SCN)2(H2synthesized and characterized by X-ray diffraction methods, IR andOctober 2004

2H2O (MZNi(II), Co(II); ampymZ2-aminopyrimidine) have beend-field spectra. The Ni(II) and Co(II) compounds, which crystallizeiversity, P.O. Box 9502, 2300 RA Leiden, The Netherlands.

alitica, Chimica Fisica, Universitadegli Studi di Parma,and solvatochromism of a Ni(II)

aminopyrimidine as a ligand

, Gerard A. van Albadaa,fredib, Jan Reedijka,*

re 734 (2005) 8388

www.elsevier.com/locate/molstrucrange with a Cary 50 Varian UV/vis/NIR spectrometer.

Electrospray ionization mass spectra (ESI-MS, Positive ion)

in MeOH solutions were recorded on a Thermo Finnigan

doi:10.1016/j.molstruc.2004.09.007

* Corresponding author. Tel.: C31 71 5274450; fax: C31 71 5274671.

E-mail address: reedijk@chem.leidenuniv.nl (J. Reedijk).solvent or pollutant molecules [8].device, using the diffuse reflectance technique. The UV/vis

spectrum of the compound was recorded in the 250800 nm

AQA apparatus. The ligand-field spectra of the solid

samples were recorded in the 2002000 nm range on a

PerkinElmer Lambda 900 UV/Vis/NIR spectrometer in the

diffuse reflectance mode with MgO as a reference. The

conductivity measurement was performed with a Philips

PW 9526 digital conductivity meter and PW 9551/60

measuring cell with a 1 mM solution of the complexes in

MeOH, H2O and MeCN.

2.2. General synthesis of the complexes

Ni(NO3)2$6H2O (10 mmol, 2.9 g) dissolved in water(10 mL) was added to a solution of NH4SCN (20 mmol,

1.5 g) in water (30 mL), and the 2-aminopyrimidine

(20 mmol, 1.9 g) in 20 mL of methanol was added to the

well stirred aqueous solution. The resulting solution was

filtered and left to evaporate at room temperature. Blue

crystals were collected after 1 week. Yield 62%. For the

Ni(II) Compound (1): ESI-MS: m/zZ438.2; Elementalanalysis [found(calc.)] for C10H18NiN8O4S2: C 27.5 (27.4);

H 4.3 (4.1); N 25.7 (25.6); S 14.5 (14.6). IR (cmK1):

3460.3 (w), 3330.4 (m), 2084.7 (s), 1629.0 (s), 1569.7 (s),

1489.4 (s), 1360.0 (s), 1195.8 (s), 787.0 (s), 660.2 (s),

523.7 (s). (w, m and s represent the intensity of the

absorption peaks as weak, medium and strong,

respectively).

The Co(II) compound (2) was synthesized in the similar

way, and blue crystals were collected after about 1 week.

Yield 60%. ESI-MS: m/zZ438.4. Elemental analysis[found(calc.)] for C10H18CoN8O4S2: C 27.5 (27.4); H 4.2

(4.1); N 25.7 (25.6); S 14.5 (14.6). IR (cmK1): 3462.0 (w),

3332.0 (m), 2075.7 (s), 1627.9 (s), 1569.9 (s), 1486.0 (s),

1358.8 (m), 787.4 (m), 659.7 (m), 522.0 (m).

2.3. X-ray crystallographic study

The molecular structure of both [M(ampym)2(SCN)2(H2O)2]$2H2O (MZNi(II) and Co(II)) was determined bysingle-crystal X-ray diffraction methods. Crystallographic

and experimental details for the two structures are summar-

ized in Table 1. Intensity data and cell parameters were

recorded at room temperature (25 8C) on a Bruker AXSSmart 1000 single-crystal diffractometer (Mo Ka radiation)equipped with a CCD area detector. The data reduction was

performed using the SAINT and SADABS programs [9].

The structure was solved by Direct Methods using the

SIR97 program [10] and refined on F02 by full-matrix least-

squares procedures, using the SHELXL-97 program [11].

All non-hydrogen atoms were refined with anisotropic

atomic displacements. The hydrogen atoms were located

in the difference Fourier map with the exception of

the hydrogen atoms of the water molecules of

Table 1

Crystallographic data for [M(ampym)2(SCN)2(H2O)2]$2H2O (MZNi(II) and Co(II))

H2O)

]

10;K

.0840

.0890

er of r

Y. Song et al. / Journal of Molecular Structure 734 (2005) 838884Compound [Ni(ampym)2(SCN)2(

Empirical formula C10H18N8NiO4S2Formula weight 437.15

Crystal system Triclinic

Space group PK1 (no. 2)

a (A) 7.259(5)

b (A) 7.895(5)

c (A) 9.065(5)

a (8) 67.578(5)

b (8) 72.511(5)

g (8) 76.860(5)

V (A3) 454.3(5)

Z 1

Dcalcd (g/cm3) 1.598

m(mmK1) 1.331

Crystal size (mm) 0.13!0.16!0.20

F(000) 226

T (K) 293(2)

Radiation (A) 0.71069

Reflections collected 5109

Indipendent reflections 2050 [R(int)Z0.0340Observed reflections [IO2s(I)] 1467Data/restraints/parameters 2050/7/143

q range for data collection (8) 2.528.0

Index ranges K9%h%9; K9 %k%Goodness-of-fit on F2 a 0.921

Final R indices (obs. data)b R1Z0.0384, wR2Z0R indices (all data)b R1Z0.0613, wR2Z0Largest diff. peak and hole (e/AK3) 0.422 and K0.423

a Goodness-of-fit SZP

WFo KFc2nKp1=2 , where n is the numb

P P P P 1=2b R1 Z sFojKFcs jFoj; wR2 Z WFo KFc2 WFo .2]$2H2O [Co(ampym)2(SCN)2(H2O)2]$2H2O

C10H18CoN8O4S2437.37

Triclinic

PK1 (no. 2)

9.145(3)

7.943(3)

7.328(3)

103.311(5)

107.381(5)

67.378(5)

464.9(3)

1

1.562

1.180

0.16!0.18!0.24

225

293(2)

0.71069

3884

1926 [R(int)Z0.0169]1839

1926/0/143

2.527.6

11%l%11 K11%h%11; K9%k%10; K9%l%91.08

R1Z0.0288, wR2Z0.0864R1Z0.0301, wR2Z0.08760.500 and K0.345

eflections and p the number of parameters.

Molecular geometry calculations were carried out using

the PARST97 program [12]. Drawings were obtained by

ORTEP3 in the WinGX suite [13]. All calculations were

carried out on a DIGITAL Alpha Station 255 computer.

3. Results and discussion

3.1. Description of the structure

[M(ampym)2(SCN)2(H2O)2]$2H20 (MZNi(II) and Co(II))

The Ni(II) and Co(II) compounds are isostructural with

the metal ion lying on an inversion center; an ORTEP view

of the Ni(II) compound is depicted in Fig. 1. Selected bond

distances and angles for both complexes are reported in

Table 2.

A slightly distorted octahedral coordination is observed

around both metal ions: four short in-plane bonds involve

two trans oxygens from the water molecules [NiO1Z2.072(2) A,CoO1Z2.093(2) A] and two trans nitrogenatoms from the thiocyanate groups [NiN4Z2.058(3) A,CoN4Z2.107(2) A]. The axial positions are

Y. Song et al. / Journal of Molecular Structure 734 (2005) 8388 85Fig. 1. An ortep view (20% probability) of [Ni(ampym)2(SCN)2(H2O)2]$crystallizations. The weighting scheme used in the last

cycle of refinement was wZ1=s2F20 C0:0456P2 and wZ1=s2F20 C0:0582P2C0:1432P (where PZF20 C2F2c =3)for (1) and (2), respectively.

2H2O with the used atomic numbering scheme.

Table 2

Selected bond lengths (A), angles (8) and hydrogen bonding parameters for [M(a

[Ni(ampym)2(SCN)2(H2O)2]$2H2O

Bond lengths: Ni1O1 2.072(2); Ni1 N4 2.058(3); Ni1N1 2.147(2)

Bond angles: O1Ni1N1 89.38(8); N4Ni1O1 91.71(10); N4Ni1N1 92.04(1

Hydrogen bonds

DH/A H/A(A)N3H1N/O1 2.23(4)N3H1N/N4 2.48(3)N3H2N/S1 (1Kx, Ky, 2Kz) 2.62(2)O1H2S/O1S 1.88(3)O1H1S/O1S (Kx, 1Ky, 1Kz) 1.90(3)C4H4/N4 (1Kx, 1Ky, 1Kz) 2.69(4)C4H4/O1 (1Kx, 1Ky, 1Kz) 2.66(3)[Co(ampym)2(SCN)2(H2O)2]$2H2OBond lengths: Co1O1 2.093(2); Co1N4 2.107(2); Co1N1 2.217(2)

Bond angles: O1Co1N4 88.71(7); O1Co1N1 91.06(6); N4Co1N1 92.29(6

Hydrogen bonds

DH/A H/A(A) D/A (A) DH/A(8)N3H2N/O1 (2Kx, 1Ky, Kz) 2.29(4) 2.983(3) 134(4)N3H2N/N4 2.49(3)N3H1N/S1 (1Kx, 2Ky, Kz) 2.67(3)O1H2S/O1S (2Kx, 1Ky, 1Kz) 1.97(3)O1H1S/O1S 2.06(4)C4H4/N4 (2Kx, 1Ky, Kz) 2.78(4)C4H4/O1 2.78(3)3.123(3) 128(3)

3.522(3) 170(3)

2.768(2) 170(4)

2.773(3) 167(3)

3.135(3) 107(2)occupied by the N1 endocyclic nitrogen from two trans-

oriented ampym ligands [NiN1Z2.147(2) A,CoN1Z2.217(2) A]. The S1C5N4 thiocyanate groups are nearly

linear with angles of 178.0(3)8 and 177.9(2)8 for the Ni(II)and Co(II) compounds, respectively. The thiocyanate groups

are not linear coordinated to the metal ions (angles MNC

are 153 and 1548 for MZCo, and Ni, respectively), and theorigin from the deviation of 1808 appears to be related tothe hydrogen bonding in the lattice. The dihedral angles that

the least-square plane through NIN2C1C2C3C4 forms

mpym)2(SCN)2(H2O)2]$2H2O (MZNi(II) and Co(II))

0); S1C5N4 178.0(3); Ni1-N4C5 153.7(2)

D/A (A) DH/A(8)2.934(2) 134(2)

3.073(4) 124(2)

3.499(3) 164(1)

2.768(3) 169(3)

2.771(4) 164(2)

3.077(5) 105(2)

3.130(4) 111(2)

); N4C5S1 177.9(2); Co1N4C5 151.0(2)3.220(3) 107(2)

with the equatorial plane, with the N1MO1 and with

N1MN4 moieties are 87.4(1), 43.8(1) and 47.9(1)8 in the

Ni(II) compound and 87.0(1), 44.4(1) and 46.9(1)8 in the

Co(II) complex.

To the best of our knowledge, the only related Ni(II) or

Co(II) complexes containing two ampym and two water

molecules in an octahedral arrangement around the metal

ion is the polymeric compound [Ni(SO4)(C4H5N3)2(H2O)2]$C6H5N3 [5]. In this complex, the sulfate ion actsas a bridging moiety between the metal atoms which

present, in the equatorial plane, two mutually cis nitrogen

atoms from ampym and two mutually cis oxygen atoms

from the water molecules.

The configuration of the present complexes, with the

ampym ligands almost orthogonal to the equatorial plane

and nearly bisecting the O1MN4 bond angles, is

bonds, also the intramolecular bifurcated interactions

CH/N(NCS) and CH/O(coordinated H2O) involvingthe ampym C4H4 group [C4/N4Z3.077(5) A, C4/O1Z3.130(4) A for the Ni(II) complex; C4/N4Z3.135(3) A, C4 /O1Z3.220(3) A for the Co(II)compound].

3.2. Infrared spectroscopy

The position of the bands of the thiocyanate group related

to the stretching frequency of the CN moiety can be used to

characterize the coordination mode of this ligand to the

metal ions. The CN stretching of a bridging thiocyanate is

usually found to be above 2100 cmK1 [14]. In the case of the

nickel(II) complex, the stretching frequency of the thiocya-

nate occurs at 2084 cmK1, which indicates normal end-on

NCS coordination. The bands corresponding to the stretch-

ing frequency of CS and NCS appear at 787 and 463 cmK1,

which is in good agreement with an end-on NCS

coordination. For the Co(II) complex, the typical stretching

frequency for the thiocyanate group can be observed at

2075 cmK1, while the band belonging to CS and the

deformation frequency NCS occur at 787 and 459 cmK1,

Y. Song et al. / Journal of Molecula86correlated to the bifurcated intramolecular hydrogen bonds

that a NH group from the ampym NH2 moieties forms with

the oxygen and nitrogen atoms of the adjacent water and

thiocyanate ligands [N3/O1Z2.934(4) A,N3/N4Z3.073(4) A for the Ni(II) complex; N3/O1Z2.983(3) A,N3/N4Z3.123(2) A for the Co(II) compound; see alsoTable 2].

The structure is further stabilized by intermolecular

interactions between the other hydrogen atom of the NH2groups and sulfur atoms from neighboring complexes

[N3/S1Z3.499(3) A in NiII compound and N3/S1Z3.522(2) A in CoII complex] and by intermolecular hydro-

gen bonds that the coordinated water molecules form, as

hydrogen donors, with the solvate ones [O1/O1SZ2.768(3) and 2.771(4) A for the Ni(II) complex; O1/O1Sand O1/O1SZ2.768(2) A for the Co(II) compound; seealso Table 3].

The inversion-related aromatic rings show a slipped

stacking to form chains running along the [001] (Ni) and

[100] (Co) directions with the shortest ringring distance of

3.324(4) and 3.342(4) A in the Ni(II) and Co(II)

Table 3

UV/vis absorption of the two complexes in different solvents

Complexes/

solvents/color

l (nm) and 3 (l molK1 cmK1)

[Ni(ampym)2(SCN)2(H2O)2]$2H2O

[Co(ampym)2(SCN)2(H2O)2]$2H2O

MeCN 383 (72.6); 625 (23.1);

light blue

563 (200.4); 630 (562);

blue

EtOH 400 (272); 664 (35);

737 (26); light green

480 (33.2); 524 (46.8);

556 (44.2); 620 (57.1);

blue purple

DMF L402 (182); 679 (42);

737 (26); light green

485 (45.6); 587 (202);

625 (346); blue

Ether Green (weak solubility) 563 (104.6); 610 (214.6);

635 (240.6); skyblue

MeOH 397 (25.2); 666 (11.0);

737 (10.0); light blue

519 (42.4); 480 (30.2);

pink

Aceton Green (weak solubility) 537 (214.0); 632 (449.2);

774 (9.6); deep bluecompounds, respectively (see Fig. 2). Also these inter-

actions contribute to the stability of the complexes.

Although the two structures are very similar, slight

differences are visible. In the Ni(II) complex, the nearest

atom to the metal center is the equatorial nitrogen N4, while

in the Co(II) compound, it is the equatorial oxygen O1 from

the coordinated water molecule. This slight distortion from

octahedral could be induced by the hydrogen bond network,

which involves, besides the above cited hydrogen

Fig. 2. Crystal packing of the [M(ampym)2(SCN)2(H2O)2]$2H2O complex

(MZNi(II) and Co(II)) showing the pp interactions between the aromaticrings of neighboring molecules.

r Structure 734 (2005) 8388respectively.

3.3. Ligand-field spectroscopy

The diffuse reflectance spectra of the solid Ni(II)

compound shows three strong bands at 9.8!103 cmK1

(s1;3A2g

3T2g), 15.8! 103 cmK1 (s2;

3A2g3T1g(F)) and

25.7! 103 cmK1 (s3;3A2g

3T1g(P)), which are the typical

absorption bands for an octahedral Ni(II) complex[15]. Two

strong bands at 30.3! 103 and 33.3!103 cmK1 are alsovisible, which are attributable to the LMCT from the ligands

to the Ni(II) atom. The value calculated by semi-empirical

equation[15] for the Dq (the crystal-field parameter), B

(Racah parameter) and Dq/B are 980, 806 and 1.21 cmK1,

respectively.

The ligand-field spectrum of the solid Co(II) compound

shows a strong band at 30.7!103 cmK1 corresponding tothe ligand to metal charge transfer (LMCT) band, while

3 K1 4 4

compound can be found around 456, 506 nm in water and

619 nm, respectively.

The solvatochromism is caused by the different coordi-

Y. Song et al. / Journal of Molecula478, 510 nm in MeOH, respectively. In ethanol, 3 dd bands

can be seen clearly in the UV/vis spectrum at 470 nm,

520 m and 604 nm. When the solvent used is MeCN, the

dd bands shift significantly to around 561 and 627 nm,

which indicates the change of the coordination geometry

around Co(II). The charge transfer band which is a shoulder

Fig. 3. UV/Vis spectra of [Co(ampym)2(SCN)2(H2O)2]$2H2O in MeCN

(8.1!10K4 m), Acetone (9.2!10K4 M), Diethyl Ether (3.1!10K3 M),the bands at 19.9!10 cm (s3; T1g(P) T1g(F)) and8.9!103 cmK1 (s1;

4T2g4T1g) are typical for octahedrally

coordinated Co(II) with this chromophore[16]. However, the

band for the transition from 4A2g4A1g (s2) is not observed in

the spectrum. The value calculated for the Dq, B and Dq/B [16]

are 890, 811 and 1.10 cmK1, respectively.

3.4. UV/vis spectra in solution

The two compounds exhibit solvatochromism (Table 3

and Fig. 3), and in the case of the Co(II) complex, the color

changes from light pink (in H2O), to pink (in MeOH), blue

purple (in EtOH) and sky blue (in diethyl ether) to deep blue

(in DMF, Aceton, MeCN). The dd bands of the Co(II)DMF (7.0!10K4 M), EtOH (3.1!10K3 M) and MeOH (3.3!10K3 M).nation of the solvents to the metal centers and the resulting

change of the coordination environment around the metal

ions. For the Co(II) complex, the blue color in several

different solvents indicates that the geometry around

the metal must be distorted to tetrahedral or square

pyramidal. When the coordinated water molecules in

[Co(II)(ampym)2(SCN)2(H2O)2]$2H2O are replaced byother solvents like aceton or acetonitrile, the coordination

around Co(II) may change from octahedral to a tetra- or

penta- coordination. For the Ni(II) complex, the color

change is not so evident, which may indicate that the

octahedral geometry around Ni(II) is maintained by

replacing the water molecules with different solvents.

The conductivities of these two complexes have been

studied in MeOH, water and MeCN. The obtained values are

quite small in MeOH and H2O, which is logical because the

complexes are crystallized from the mixture of MeOH and

water, and no dissociation occurs. In MeCN, the conduc-

tivities of these two compounds are still below 40 cm2 UK1

molK1, confirming that the thiocyanate groups are not

dissociated from the metal ions too. Therefore, though the

geometry around the metal ions may change in different

solvents, the thiocyanate groups are still kept in the

coordination surrounding around the metal ions.

4. Conclusions

In the present paper, two mononuclear isostructural

Ni(II) and Co(II) complexes have been obtained, which

show an octahedral geometry around the metal ions. Their

crystal structures are stabilized by hydrogen bonding and

pp interactions between 2-aminopyrimidine rings fromdifferent molecules. Both the compounds show solvatochro-

ism which is due to the substitution of the water molecules

arranged in an octahedral geometry around Ni(II) and Co(II)

by other solvents. The change of the geometry and

coordination environment around the metal centers leads

to the color change and the shift of the charge transfer andpeak at around 320340 nm is overlapped by a very strong

band around 290 nm in different solvents. So we believe that

tetrahedral Co(II) or 5-coordinate Co(II) is present in the

aprotic solvents.

For the Ni(II) complex, the color changes are not so

strong, from light blue (MeOH, H2O), to light green (EtOH)

and to green (Ether, Aceton). The UV absorption bands can

be found in the region of 388395 nm for the LMCT and

two dd bands (one is in the range of 645654 and another

one is in the range of 708720 nm, see Table 3) in water,

methanol, EtOH and DMF. In Ether and MeCN, the charge

transfer band shifts to 379 and 374 nm, and only one dd

band in the visible range can be observed at 623 and

r Structure 734 (2005) 8388 87dd bands in different solvents.

5. Supplementary material

Crystallographic data (excluding structure factors) for

the structures reported have been deposited with the

Cambridge Crystallographic Data Center as supplementary

publication no. CCDC-242651 and 242652 for compounds

(1) and (2), respectively, and can be obtained free of charge

on application to the CCDC, 12 Union Road, Cambridge

CB2 1EZ, UK. [Fax: (Internet.)C44-1223/336-033;e-mail: deposit@ccdc.cam.ac.uk]

Acknowledgements

The work described here has been supported by the

Leiden University Study group WFMO (Werkgroep Fun-

damenteel Materialen-Onderzoek). Support from the NRSC

Catalysis (a Research School Combination of HRSMC and

NIOK) is kindly acknowledged.

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Synthesis, structural characterisation and solvatochromism of a Ni(II) and a Co(II) compound with 2-aminopyrimidine as a ligandIntroductionExperimental sectionGeneral remarks and physical measurementsGeneral synthesis of the complexesX-ray crystallographic study

Results and discussionDescription of the structure [M(ampym)2(SCN)2(H2O)2].2H20 (M=Ni(II) and Co(II))Infrared spectroscopyLigand-field spectroscopyUV/vis spectra in solution

ConclusionsSupplementary materialAcknowledgementsReferences