synthesis and x-ray crystal structures of 1 : 1 complexes of nickel(ii) nitrate with...

Polyhedron Vol. 8, No. 5, pp. 689-693,1989 Printed in Great Britain

0277-5387/89 S3.00+.00 Q 1989 Per@mon Press plc

SYNTHESIS AND X-RAY CRYSTAL STRUCTURES OF 1: 1 COMPLEXES OF NICKEL(H) NITRATE WITH l,lO- PHENANTHROLINE AND WITH 2,2’-BIPYRIDYL

FRANK WALMSLEY, A. ALAN PINKERTON and JUDITH A. WALMSLEY*

Department of Chemistry, University of Toledo, Toledo, OH 43606, U.S.A.

(Received 27 August 1988 ; accepted 5 October 1988)

Abstract-Blue crystals of [Ni(phen)(H20)4](N03)2* HZ0 (where phen = l,lO-phenanthroline) and of ~i~bipy)~*O)~(NO~)]NO~ (where bipy = Z,~-bipy~dyl) were prepared and their structures determined by single crystal X-ray crystallography. In the phenanthroline complex, the nitrates are not coordinated to the nickel but in the bipyridyl complex, one nitrate is coordinated to the nickel as a monodentate ligand. The IR spectra and magnetic susceptibilities are reported.

Transition metal complexes of 1, IO-phenanthroline (phen) and 2,2’-bipyridyl (bipy) have been of interest for many years. Among other uses, these complexes have been part of an effective method for metal analysis. Additional knowledge about the structure of complexes that may exist in aqueous solution is of potential value in understanding inter- mediates in ligand exchange reactions in aqueous solution. Nickel(I1) complexes have been of special interest including reports of spectral and magnetic properties’ and of formation constants.* With three ligands per nickel, the complexes are usually red, with two per nickel they are usually pink or violet, and with one per nickel, blue ; there are, of course, numerous exceptions to these generalities. ’ While structures of 1: 1 complexes of nickel(I1) sulphate with these ligands have been reported,3*4 little is known about 1 : 1 nickel(I1) nitrate complexes. We report the preparation and structure of two such complexes, including IR and magnetic susceptibility data.

EXPERIMENTAL

Synthesis

(Ni(phen)(H,0),](N03)2 * H20. Reagent grade Ni(NO& * 6H20 (5.81 g, 20 mmol) was dissolved

*Author to whom correspondence should be addressed. Present address : Division of Earth and Physical Sciences, U~~e~ity of Texas at San Antonio, San Antonio, TX 78285, U.S.A.

in 5 cm3 of deionized distilled HzO. l,lO-Phen- anthroline monohydrate (0.80 g, 4 mmol) was added to the Ni(N03)z solution with stirring. The solid phenanthroline slowly dissolved. Initially, some pink solid formed which subsequently dissolved forming a blue solution. A small amount of unreacted phenanthroline was filtered off. The solution was allowed to evaporate slowly until blue crystals formed. Under a microscope it was possible to see two types of crystals. The major component was blue rods and these were the crystals used in this study. The minor component appeared as blue needles. A few purple crystals (probably bis or tris complexes) were observed and were removed prior to use for measurements requiring bulk samples.

~i(bipy)(H~O)~(NO~)]NO~. Reagent grade Ni(NO~)~*6H~O (5.81 g, 20 mmol) was dissolved in 5 cm3 of deionized distilled H20. 2,2’-Bipyridyl (0.63 g, 4 mmol) was added to the Ni(NO& solution with stirring and slight warming. The solid bipyridyl slowly dissolved with some of the solid turning pink before dissolving to give a blue-green solution. The solution was allowed to evaporate slowly until blue plate-like crystals formed.

IR and magnetic susceptibility

IR spectral measurements were made as reflec- tance spectra, using KBr as diluent, on a Nicolet SX-60 FTIR instrument under standard operating conditions (4 cm-’ resolution). Magnetic susceptibility measurements were made by the Gouy method at 20°C as previously reported. 5

690 F. WALMSLEY et al.

Table 1. Summary of the crystal data and refinement results

Molecular formula Formula weight Space group

a (A) b (A) c (A) B (“) v (A’) z

&,, (g cm- 3, ~(Mo-K,) (cm- ‘) Crystal dimensions (mm) Temperature (“C) Reflections measured Maximum 20 (“) Agreement factor, R :

unweighted weighted

[Ni(phen)(H,0),l(N03),.H,0 C12H18NiN4011 435.01

P2,lc 8.745( 1) 13.591(2) 15.336(3) 94.61(l) 1816.8 4 1.66 11.3 0.12 x 0.18 x 0.21 2151 4303 (3722 unique) 53.0

N(Wy)(H 0) ANO d1N03 GoH14NiN409 392.95

P2,lc 11.459(3) 9.433(2) 14.809(3) 109.88(2) 1505.2 4 1.73 13.5 0.32 x 0.22 x 0.08 21+1 3303 (3145 unique) 52.0

Crystal structures

Preliminary examination and X-ray intensity data collections were performed on an Enraf- Nonius CAD4 automatic kappa axis diffract- ometer equipped with a graphite crystal, incident beam monochromator (MO-K,, 1= 0.71073 A). Calculations were carried out on a VAX 1 l/750 computer using VLXSDP. Both structures were solved using conventional Patterson and Fourier techniques and refined by full-matrix least- squares. A summary of the crystallographic data is given in Table 1. *

RESULTS AND DISCUSSION

l?When)(H~W(NW 2 * Hz0

The X-ray crystal structure results as shown in Fig. 1 reveal an octahedral environment of ligands around the nickel composed of one bidentate 1, lo- phenanthroline molecule and four water molecules. The nitrate ions are not coordinated to the nickel and are thus considered to be ionic. The bond lengths of the atoms bonded to the nickel are listed in Table 2, and the bond angles which include the nickel atom are listed in Table 3.

* Final positional and thermal parameters, a list of all bond lengths and angles, a table of some geometrical features, and a list of the observed and calculated structure factors have been deposited as supplementary material with the Editor, from whom copies are available on request. Atomic coordinates have also been deposited with the Cambridge Crystallographic Data Centre.

Fig. 1. ORTEP view of the nickel environment in [Ni(phen)(H,O),](NO,), - H,O. Atoms are represented

by 50% probability ellipsoids.

Table 2. Selected bond distances (A) for [Ni(phen)

(HO&NW~ - Hz0

Atom 1 Atom 2 Distance

Ni N(1) 2.062(5) Ni N(2) 2.051(6) Ni O(1) 2.099(5) Ni O(2) 2.095(5) Ni O(3) 2.064(5) Ni O(4) 2.041(5)

Numbers in parentheses are estimated standard deviations in the least significant digits.

Phenanthroline and bipyridyl complexes of Ni” 691

Table 3. Selected bond angles (“) for [Ni(phen) W,W(NW,-Hz0

b

Atom 1 Atom 2 Atom 3 Angle

N(1) Ni N(2) 81.3(2)

N(1) Ni O(2) 92.2(2)

N(1) Ni O(4) 95.7(2)

N(1) Ni O(3) 174.0(2)

N(1) Ni O(1) 92.6(2)

N(2) Ni O(l) 95.4(2)

N(2) Ni O(3) 92X(2)

N(2) Ni O(4) 177.0(2)

N(2) Ni O(2) 92.4(2)

O(1) Ni O(2) 171.4(2)

O(1) Ni O(3) 87.2(2)

O(l) Ni O(4) 84.4(2)

O(2) Ni O(4) 88.1(2)

O(2) Ni O(3) 88.8(2)

O(3) Ni O(4) 90.2(2)


c L

Wavenumber I cm -1

Fig. 2. IR absorptions in the 1700-1800 cm-’ region:

(a) WWen>W~W(NW2 -I-LO and 04 W(biw) G-LOMNWINO,.

The bond lengths and angles are in agreement with those reported for other phenanthroline complexes of nickel.6 It has been suggested that the bite of the phenanthroline molecule is inflexible ; thus the N-M-N angle changes only as a result of a change in the M-N distance due to a change in the radius of the metal.6 This inverse relationship between the M-N distance and N-M-N angle has been documented.6 In comparison with the Ni(phen):+ ion, the average Ni-N distance in Ni(phen)(H,O)z+ is less (2.056 vs about 2.090 A) and the average N-Ni-N angle is greater (81.3 vs about 79.4”). Thus the nickel atom with one phenanthroline attached appears to be smaller than a nickel atom with three phenanthrolines attached. This may be due to the bulk of three phenanthroline molecules causing steric repulsions, resulting in each phenthroline moving away from the nickel atom to reduce the repulsions. This may also be due to metal-ligand back bonding. With one phenanthroline molecule, the amount of back bonding to the phenanthroline will be greater. When there are three phenanthroline molecules, the electron density donated from the nickel must be distributed among the three ligands, resulting in a lesser amount of back bonding per phenanthroline. A greater amount of back bonding increases the metal-ligand bond order and reduces the bond length in the case with one phenthroline compared to the case with three phenanthrolines.

Nitrate groups exhibit absorptions in the IR region of 1700-1800 cm-’ which are due to com- binations of fundamental frequencies. The absorptions in this region have been used to distinguish among the various coordination modes of the nitrate group : ionic, monodentate, bidentate and bridging.7 Ionic nitrates are expected to have a single absorption in the IR spectnun in this region.7 As shown in Fig. 2(a), this compound has an expected single absorption at 1770 cn- ‘. This single absorption indicates the presence of ionic nitrate which is in agreement with the X-ray crystal structure which shows no coordinated nitrates.

The X-ray crystal structure results as shown in Fig. 3 reveal an octahedral environment of ligands

The magnetic moment of mi(phen)(H,O)J Fig. 3. ORTEP view of the nickel environment in [Ni (NO,), - H,O is 3.11 BM at 2O”C, which is typical (bipy)(H,O),(NO,)]NO,. Atoms are represented by 50% for octahedral nickel(I1). probability ellipsoids.

692 F. WALMSLEY et al.

Table 4. Selected bond distances (A) for [Ni(bipy)

@L0h(NWINO,

Atom 1 Atom 2 Distance

Ni N(1) 2.045(2) Ni N(1’) 2.061(3) Ni O(l) 2.103(2) Ni O(4) 2.038(2) Ni O(5) 2.072(2) Ni O(6) 2.056(3)


around the nickel, composed of one bidentate 2,2’- bipyridyl molecule, three water molecules, and one monodentate nitrate ligand. The second nitrate is not coordinated to the nickel and is thus considered to be ionic. The bond lengths of atoms bonded to nickel are listed in Table 4 and the bond angles which include the nickel atom are listed in Table 5.

The bond lengths and angles are in agreement with those reported for other 2,2’-bipyridyl complexes of nickel. 3,4 It has been reported that coordinated metal-water distances are shorter when the water is trigonal rather than tetrahedral.4 Of the three coordinated water molecules in this structure, one [O(4)] has a distinctly shorter bond distance than the other two and similar to the short bond distance in the compound of Healy.4 Coordinated water molecules referred to as trigonal water are actually planar or nearly planar. By comparing deviations from planarity, it is possible to distinguish between trigonal and tetrahedral water

Table 5. Selected bond angles (A) for [Ni(bipy) (H,%Wb)lNO~

Atom 1 Atom 2 Atom 3 Angle

N(1) Ni NU’) 79.q 1) N(1) Ni O(1) 92.54(9)

N(1’) Ni O(l) 98.9(l) N(1) Ni O(4) 176.2(l)

N(1) Ni O(5) 92.81(9)

N(1) Ni O(6) 89.9( 1)

N(1’) Ni O(4) 96.8( 1) N(1’) Ni O(5) 172.30(8) NU’) Ni O(6) 91.1(l) O(4) Ni O(5) 90.9( 1) O(4) Ni O(6) 91.0(l) O(5) Ni O(6) 89.3(l) O(l) Ni O(4) 87.2( 1) O(l) Ni O(5) 80.86(g) O(1) Ni O(6) 170.0(l) O(4) Ni O(6) 91.0(l)


Table 6. Deviations (A) from the best plane for each Ni--C)H, in [Ni(bipy)(H,O),(NO,)]NO,

O(4) O(5) O(6) Ni -0.013 -0.043 - 0.020 0 0.084 0.248 0.115 H - 0.027 -0.102 - 0.044 H - 0.044 -0.103 -0.051

molecules. The data in Table 6 indicate the deviations from the best plane for each of the three water molecules including the nickel atom in the plane. The water labelled O(4) has a small deviation from planarity and is presumably trigonal. This water molecule also has a short Ni-0 distance (2.038 A) in agreement with the previous report.4 The other two water molecules have larger deviations from planarity with the water containing O(6) being more planar than the water containing O(5). The bond orders also increase in the same way that planarity decreases ; that is, the N&O(6) distance is shorter than the N&O(5) distance. Another way to consider this is to compare the H-O-H angles, although this is less sensitive due to the greater uncertainty in locating the hydrogen atoms. The H-O-H angles decrease from 112” for H--0(4)-H, to 111” for H-0(6)-H, to 97” for H--0(5)--H, the same order as the changes in the Ni-0 distances.

The X-ray crystal structure shows that one of the two nitrate groups is bonded to the nickel through one oxygen-a monodentate nitrate group. Mono- dentate nitrate ligands bonded to nickel are expected to have two absorptions in the IR region between 1700 and 1800 cm-’ with a separation of about 2&25 cm- . ’ 7 As shown in Fig. 2(b), the IR spectrum in this region has absorptions at 176 1 and 1784 cm- ‘, a separation of 23 cm- ‘. The X-ray crystal structure also shows that one of the nitrate groups is not coordinated to the nickel-an ionic nitrate. An ionic nitrate normally would be expected to have a single absorption in this region, just as in the phenanthroline complex. Thus, a monodentate nitrate plus an ionic nitrate would normally give three absorptions in this region. Only the two absorptions due to the monodentate nitrate are observed. Why is the ionic nitrate absorption missing? Some compounds with ionic nitrates that do not have any absorptions in this region have been reported. 7 These compounds are all hydrates, as opposed to anhydrous salts such as NaNO, and Sr(N03)2, and it was suggested7 that extensive hydrogen bonding may be responsible. The X-ray data show that all the oxygens of the ionic nitrate group receive hydrogen bonds in the bipyridyl complex, which is in agreement with the suggestion.

Phenanthroline and bipyridyl complexes of Ni” 693

The magnetic moment of [Ni(bipy)(H,O), 2. (NO,)]NO, is 3.51 BM at 20°C. This is slightly 3. high for octahedral nickel(II), but deviations from a regular octahedron as exhibited by this 4. complex tend to raise the magnetic moment.

5.

REFERENCES 6.

1. C. M. Harris and E. D. McKenzie, J. Znorg. Nucl. 7. Chem. 1967,29,1047.

W. A. E. McBryde, Can. J. Chem. 1967,45,2093. J.-C. Tedenac and E. Philippot, Acta Cryst. 1974, B30,2286. P. C. Healy, J. M. Patrick and A. H. White, Aust. J. Chem. 1984,37,921. A. G. Menke and F. Walmsley, Znorg. Chim. Acta 1976, 17, 193. B. A. Frenz and J. A. Ibers, Znorg. Chem. 1972, 11, 1109. A. B. P. Lever, E. Mantovani and B. S. Ramaswamy, Can. J. Chem. 1971,49, 1957.

synthesis and x-ray crystal structures of 1 : 1 complexes of nickel(ii) nitrate with...

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