acetato axial ligands

Inorganica Chimica Acta 358 (2005) 1096–1106 www.elsevier.com/locate/ica

Manganese (III) cyclam complexes with aqua, iodo, nitrito, perchlorato and acetic acid/acetato axial ligands Susanne Mossin

b

a,*

, Henning Osholm Sørensen b,1, Høgni Weihe a, Jørgen Glerup a, Inger Søtofte c

a Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark Centre for Crystallographic Studies, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark c Department of Chemistry, Building 207, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

Received 7 September 2004; accepted 4 October 2004

Abstract The syntheses, structures and magnetic properties of five new manganese (III) cyclam complexes, trans-[Mn(cyclam)(OH2)2](CF3SO3)3 Æ H2O, trans-[Mn(cyclam)I2]I, trans-[Mn(cyclam)(ONO)2]ClO4, trans-[Mn(cyclam)(OClO3)2]ClO4 and trans-[Mn(cyclam) (CH3COO)(CH3COOH)](ClO4)2, are reported. Cyclam is the tetradentate amine ligand 1,4,8,11-tetraazacyclotetradecane. The complexes all exhibit pronounced tetragonal elongation of the coordination octahedron with the four cyclam nitrogens occupying the four equatorial positions. The magnetic properties are consistent with the formulation of the complexes as high-spin d4 systems. trans-[Mn(cyclam)(OH2)2](CF3SO3)3 Æ H2O is shown to be a convenient starting material for the syntheses of trans cyclam complexes. [Mn(cyclam)(CH3COO)(CH3COOH)](ClO4)2 exhibits extremely short intermolecular hydrogen bonds resulting in a pseudo-chain structure. The tilt of the axial ligands with respect to the equatorial plane containing the manganese and the cyclam nitrogen atoms is discussed.
2004 Elsevier B.V. All rights reserved. Keywords: Manganese (III); Synthesis; X-ray; Magnetism; Axial tilt

1. Introduction Manganese (III) complexes are obvious building blocks used in the design of molecular magnets, i.e., polynuclear transition metal clusters exhibiting slow relaxation of the magnetisation [1]. This property seems to be governed by a high axial cluster anisotropy which can be obtained by incorporating into the cluster metal ions, e.g. manganese (III), known to show pronounced magnetic anisotropy. In an attempt to rationalise the *

Corresponding author. Tel.: +45 35320120; fax: +45 35320133. E-mail address: [email protected] (S. Mossin). 1 Present address: Center for Fundamental Research: Metal Structures in Four Dimensions, Risø National Laboratory, DK-4000 Roskilde, Denmark. 0020-1693/$ - see front matter
2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2004.10.005

various mechanisms governing the magnetic properties in general, and in particular the ground state magnetic anisotropy of manganese (III) complexes, we have synthesised the five new complexes, trans-[Mn(cyclam) (OH2)2](CF3SO3)3 Æ H2O (1), trans-[Mn(cyclam)I2]I (2), trans-[Mn(cyclam)(ONO)2]ClO4 (3), [Mn(cyclam)(OClO3)2]ClO4 (4) and trans-[Mn(cyclam)(CH3COO)(CH3COOH)](ClO4)2 (5). Complexes containing cations of the type trans[Mn(cyclam)X2]+ are known with X = Cl [2,3], Br [2,3], ONO2 [2], N3 [3,4], NCO [5] and CN [2,6]. Hence, with the inclusion of the complexes described in this article this series is now known with axial ligands covering most of the spectrochemical series having I
and CN
located in the lower and upper end, respectively. All the mentioned complexes, except trans-[Mn-

S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

(cyclam)(CN)2]ClO4, have a high-spin (S = 2) ground state and exhibit pronounced structural tetragonal elongation. trans-[Mn(cyclam)(CN)2]ClO4, on the contrary, has a low-spin (S = 1) ground state [2] and is slightly tetragonally compressed [6]. 1 is the first member in this series with uncharged axial ligands and is shown to be a convenient starting material for the synthesis of other complexes, since the water molecules are easily replaced by other ligands. Manganese (III) is normally considered to be fairly oxidising and, therefore, the existence of simple iodide complexes is surprising. Three earlier reports on manganese (III) iodide complexes have been supported by structural data. These contain more exotic ligands known to stabilise high oxidation states (porphyrin, phosphine, and silylamine) and not just a simple amine as in 2 [7]. Recently [8], we demonstrated that the magnetic anisotropy of 2 opposes that exhibited by all other tetragonally elongated manganese (III) complexes [9]. In view of this, it is imperative to investigate the structural parameters of 2 and to compare them with the parameters of the other complexes in the series in order to determine the origin of this deviation.

2. Experimental Magnetic susceptibility measurements were performed by the Faraday method in the temperature range 50–300 K. The molar susceptibilities were corrected for diamagnetism of ligands and counterions using Pascal
s constants [10]. The absorption spectra were measured on a Cary 5E spectrophotometer. 2.1. Syntheses Cyclam is synthesised by standard literature methods [11]. For safety reasons, we used nickel bromide instead of nickel perchlorate. The yield was 45%, whereas 63% is reported for the literature synthesis. NB! Transition metal complexes containing perchlorate ions are potentially explosive and should be handled with care and in small amounts only. 2.1.1. trans-Diaquacyclammanganese (III) triflate monohydrate, trans-[Mn(cyclam)(OH2)2](CF3SO3)3 Æ H2O (1) Cyclam (2.00 g, 10.0 mmol) was dissolved in ethanol (40 ml, 99%). Mn(CF3SO3)2 Æ 4H2O (4.26 g, 10.0 mmol) 2 2 Mn(CF3SO3)2 Æ 4H2O was synthesised from MnCO3 and triflic acid (6 M). Slightly less than the theoretical amount of triflic acid was poured onto MnCO3. The solution was passed through a paper filter, reduced on rotary evaporator, and the resulting crystals were filtered and washed with a small amount of water. The product was stored in a desiccator and used without further purification.

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in ethanol (15 ml, 99%) was added and the resulting solution was left with stirring for 1 h. A dark green precipitate of [Mn(cyclam)O]2(CF3SO3)3 Æ 3H2O formed. The solution with the precipitate was evaporated to approximately 5 ml, filtered, washed with a small amount of ethanol (96%) and dried in air. Yield: 4.15 g, 80%. The product was treated with triflic acid (CF3SO3H: 15 ml, 2 M) and after 4 h a clear violet solution resulted, which was left for evaporation and the next day large violet crystals had separated. When the solution started to lose the violet colour and turn green, the crystals were filtered off and washed with a small amount of ice-cold water and air dried. Yield: 2.40 g, 40% from the dimer. Anal. Calc. for C13H30F9MnN4O12S3: C, 20.64; N, 7.41; H, 4.00; Mn, 7.26. Found: C, 20.37; N, 7.22; H, 4.07; Mn, 7.03%. (Anal. of the Mn(III,IV) dimer [Mn(cyclam)O]2(CF3SO3)3 Æ 3H2O: Calc. for C23H54F9Mn2N8O14S3: C, 26.47; N, 10.74; H, 5.21; Mn, 10.53. Found: C, 26.34; N, 10.76; H, 5.12; Mn, 11.32%.) Crystals suitable for X-ray structure determinations were obtained directly from the synthesis. If small crystals are treated with a dry noncoordinating solvent such as methanol, the compound loses the water of crystallisation as well as one of the coordinated water molecules. 3 The loss of water is accompanied with destruction of the crystals and a change of colour from violet to red. It is reasonable to assume that a triflate anion coordinates instead of the water molecule. 2.1.2. trans-Cyclamdiiodomanganese (III) iodide, trans-[Mn(cyclam)I2]I (2) Sodium iodide (0.45 g, 3.0 mmol) in 1 ml of water was added to 1 (0.76 g, 1.00 mmol) in water (3 ml). Immediately, dark red crystals were formed and were filtered off. The crystals were washed with water, ethanol and dichloromethane. Yield: 0.62 g, 97% Anal. Calc. for C10H24I3MnN4: C, 18.89; N, 8.81; H, 3.80; Mn, 8.64; I, 59.86. Found: C, 18.98; N, 8.75; H, 3.89; Mn, 8.62; I, 60.01%. Crystals suitable for X-ray structure determinations were obtained directly from the synthesis. 2.1.3. trans-Cyclambis(nitrito)manganese (III) perchlorate, trans-[Mn(cyclam)(ONO)2]ClO4 (3) Sodium nitrite (0.17 g, 2.5 mmol) in 1 ml of water was added to 1 (0.76 g, 1.0 mmol) in water (2 ml). Sodium perchlorate (0.31 g, 2.5 mmol) was added to the green solution. After a few minutes yellow–brown crystals formed. The solution was cooled in ice water for half an hour, filtered and the crystals were washed with a small amount of water and ethanol. Yield: 0.31 g, 71%. Anal. Calc. for C10H24ClMnN6O8: C, 26.89; 3

Anal. of [Mn(cyclam)(OH2)](CF3SO3)3: Calc. for C13H26F9MnN4O10S3: C, 21.67; H, 3.64; N, 7.78. Found: C, 21.66; H, 3.62; N, 7.75%.

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S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

H, 5.41; N 18.81; Mn, 12.30. Found: C, 26.90; H, 5.35; N, 18.79; Mn, 11.88%. The crystals used for X-ray structure determinations were grown as follows: 1 (50 mg) was dissolved in 1 ml of acetonitrile in a 3 ml test tube. NaNO2 (10 mg) and NaClO4 Æ H2O (15 mg) were dissolved in water (0.5 ml) and added very carefully to the bottom of the test tube with a Pasteur pipette. Needles were formed slowly in the water–acetonitrile junction and platelets were formed fast when the two phases were mixed after approximately 20 min. 2.1.4. trans-Cyclambis(perchlorato)manganese (III) perchlorate, trans-[Mn(cyclam)(OClO3)2]ClO4 (4) 1 (0.38 g, 0.50 mmol) was dissolved in acetonitrile (5 ml). Sodium perchlorate (0.21 g, 1.5 mmol) was also dissolved and five drops of perchloric acid (6 M) were added. The solution was reduced on a rotary evaporator or by voluntary evaporation until the colour of the precipitate is pure red. The product was filtered, washed with ethanol (99%) and dried. It is best stored in a dry atmosphere. Yield: 0.25 g, 90%. Anal. Calc. for C10H24Cl3MnN4O12: C, 21.69; H, 4.37; N, 10.02; Mn, 9.92. Found: C, 21.31; H, 4.22; N, 9.68; Mn, 9.24%. X-ray quality crystals were obtained from slow evaporation of a solution of 4 in 2 M HClO4. 2.1.5. trans-(Acetato)(acetic acid)cyclammanganese (III) perchlorate, trans-[Mn(cyclam)(CH3COO) (CH3COOH)](ClO4)2 (5) 1 (0.38 g, 0.50 mmol) was dissolved in acetonitrile (5 ml). Sodium perchlorate (0.21 g, 1.5 mmol) was also dissolved and two drops of perchloric acid (6 M) were added. A solution of sodium acetate in 6 M acetic acid (pH 4) was added until the colour of the solution was constant (green). The solution was left for voluntary evaporation until the large light blue crystals had separated. The product was filtered and washed with a small amount of the acetate–acetic acid mixture. Yield: 0.20 g, 70%. Anal. Calc. for C14H31Cl2MnN4O12: C, 29.33; H, 5.45; N, 9.77. Found: C, 28.97; H, 5.27; N, 9.66%. The synthesis of previously known complexes can also be achieved from 1 with no contamination of other coordinating anions in the product. For example: 2.1.6. trans-Diazidocyclammanganese (III) triflate, trans-[Mn(cyclam)(N3)2]CF3SO3 The procedure is analogous to the synthesis of 3 but with sodium azide (NaN3, 0.16 g, 2.5 mmol). The solution turned red-orange and an orange precipitate formed within a few minutes. The product was filtered off and washed with a small amount of water and ethanol. Yield: 0.32 g, 63%. Anal. Calc. for C11H24F3MnN10O3S: C, 27.05; N, 28.68; H, 4.95; Mn, 11.25. Found: C, 27.04; N, 28.55; H, 4.91; Mn, 10.92%.

2.2. X-ray structure determinations Single crystal structure determinations were performed of 1, 2, 3 (in two polymorphic forms – 3a and 3b), 4 and 5. Data of compound 1 were collected at 122(1) K using an Enraf–Nonius CAD4 diffractometer and reduced with the programs from the DREAR program package [12]. Data of 2 were collected at 120(2) K using a Siemens SMART Platform diffractometer with a CCD detector. Data reduction for 2 was performed with the programs SAINT [13] and SADABS [14]. The data for crystals 3a, 3b, 4 and 5 were all collected at 122(1) K using a Nonius KappaCCD diffractometer and reduced with EvalCCD [15] and SORTAV [12]. All data sets were corrected for absorption effects. Data sets 2 and 5 were corrected with an empirical method [14], whereas 1, 3a, 3b and 4 were corrected using the Gaussian integration method [16]. All structures were solved by direct methods using different programs – 1 with SHELXS -97 [17], 2 with SHELXTL -94 [18] and 3a, 3b, 4 and 5 with SIR97 [19]. Refinements were performed in full-matrix least-squares mode using SHELXTL -94 [18] for 2 and SHELXL -97 [20] for the remaining. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms in the structures of 2, 3a, 3b, 4 and 5 were refined ˚ , N–H = 0.93 A ˚ using a riding model with C–H = 0.99 A ˚ and their isotropic displacement and O–H = 0.84 A parameters were constrained to 1.2 times the Ueq of the parent atom (1.5 times the Ueq for Me and OH groups). In 5 the methyl groups were refined with torsional freedom around the C–CH3 bond. The hydrogen atom involved in the very short hydrogen bond between O2 and O24 of 5 is distributed over two sites each with a population of 0.50(4). In the structure of 1, the positions and isotropic displacement parameters of the hydrogen atoms were refined independently. The absolute configurations of 3b and 5 were confirmed by the Flack parameter [21]. An extinction parameter was included in the refinement of 4. Details on the data collections and refinements can be found in Table 1.

3. Results and discussions 3.1. Synthetic aspects The coordinated water molecules in 1 are easily lost and replaced by anionic ligands. ½MnðcyclamÞðOH2 Þ2 

3þ

þ 2X


! ½MnðcyclamÞX2 þ þ 2H2 O The synthesis of other complexes from 1 is facilitated by the high solubility in water and acetonitrile. It is stable for months in weakly acidic solutions if access to air is

Table 1 Crystallographic data

Measured reflections Unique reflections Observed reflectionsa Rint Refined parameters R1 a wR(F2) Goodness-of-fit Flack parameters [21] Extinction [20] a

2

2

3a

3b

4

5

C13H30F9MnN4O12S3 756.53 triclinic P 1 9.960(2) 10.1158(19) 15.2129(16) 73.616(12) 86.282(13) 75.436(16) 1423.2(4) 2 1.765 0.803 0.34 · 0.22 · 0.16 0.826, 0.892 1.40–32.47
15 6 h 6 15;
15 6 k 6 15;
22 6 l 6 22 16 035 10 249 8828 0.0226 502 0.0367 0.0920 1.031

C10H24I3MnN4 635.97 tetragonal P42/m 8.3630(4) 8.3630(4) 12.7518(8) 90 90 90 891.86(8) 2 2.368 6.807 0.23 · 0.20 · 0.14 0.773, 1.000 2.44–29.46
11 6 h 6 11;
11 6 k 6 11;
16 6 l 6 9 6128 1225 1138 0.0283 46 0.0166 0.0388 1.139

C10H24ClMnN6O8 446.74 monoclinic P21/c 16.6560(9) 7.358(2) 14.5730(12) 90 102.809(7) 90 1741.5(5) 4 1.704 0.966 0.24 · 0.17 · 0.03 0.727, 0.972 3.04–30.05 0 6 h 6 23;
10 6 k 6 10;
20 6 l 6 19 62 697 51 00 3359 0.0556 238 0.0302 0.0679 0.941

C10H24ClMnN6O8 446.74 orthorhombic P212121 12.9860(5) 7.2230(2) 18.9230(9) 90 90 90 1774.94(12) 4 1.672 0.948 0.33 · 0.12 · 0.08 0.732, 0.940 3.23–30.03
18 6 h 6 18;
10 6 k 6 10;
26 6 l 6 26 49 550 5184 4590 0.0402 235 0.0263 0.0585 1.024
0.002(12)

C10H24Cl3MnN4O12 553.62 tetragonal P42/m 9.0330(3) 9.0330(3) 12.1110(5) 90 90 90 988.20(6) 2 1.861 1.144 0.33 · 0.30 · 0.29 0.702, 0.756 3.19–40.00 0 6 h 6 16;
16 6 k 6 16;
21 6 l 6 21 25 882 3161 2630 0.0276 75 0.0272 0.0718 1.051

C14H31Cl2MnN4O12 573.27 monoclinic P21 9.1090(2) 15.9860(4) 12.1110(5) 90 96.411(2) 90 2367.10(10) 4 1.609 0.849 0.46 · 0.22 · 0.19 0.89, 1.00 2.25–27.50
11 6 h 6 11;
20 6 k 6 20;
21 6 l 6 21 73 714 10 848 8948 0.0366 600 0.0246 0.0507 0.874 0.055(10)

S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

Formula M Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z Dc (g cm
3) l (mm
1) Crystal size (mm) Tmin, Tmax h range () Range of h, k, l

1

0.0301(16)

2

[F > 2r(F )].

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S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

3.2. Magnetic properties Magnetic susceptibility measurements from 50 to 300 K (Figs. S1–S5 in the supplementary material) are consistent with the formulation of 1, 2, 3, 4 and 5 as high-

spin d4 Mn(III) complexes. The magnetic moments are in the range 4.9–5.0 lB and are temperature independent in the range mentioned above. These values are close to the spin-only value of 4.9 lB expected for a high spin d4 electron configuration. The data for 5 also show that magnetic interactions across the acetate–acetic acid hydrogen bond bridge are limited, since the Mn(III) centres behave as isolated ions in this temperature interval.

4. Absorption spectra The absorption spectrum of 1 is shown in Fig. 1. Based on the high extinction coefficients, we assign the bands at 29 200 and at 36 800 cm
1 to charge transfer transitions. Due to their weakness and narrowness, the bands at 22 900 and 23 400 cm
1 are assigned to spin forbidden transitions to excited states originating from the same electron configuration as the ground state. The ground state electron configuration is deduced to be d1xy d1yz d1zx d1z2 , since the Mn–O bonds are longer than the Mn–N bonds, see Table 2, and in addition, water is located lower in the spectrochemical series compared to secondary amines [23]. The energetically lowest triplets from this electron configuration have the approximate energy 4ð5=2B þ CÞ [24], where B and C are the Racah two-electron repulsion parameters. With B and C being 80% of the free-ion values [25], the lowest spin triplets have the energy 20 750 cm
1 relative to the ground state, which is in reasonable agreement with the experiment. The band with maximum at 17 360 cm
1 is, despite its rather high energy, assigned to the transition between the two tetragonal components of the octahedral 5E term, 5B1 ! 5A1. By adding HCl or HBr to an aqueous solution of 1, this band moves continuously to lower energies until at a concentration of 4 M they stop moving at 13 000 and 12 200 cm
1, respectively. The same spectra are observed for [Mn(cyclam)Cl2]Cl Æ 5H2O and

40

15000 1 in 0.001 M C F3S O3H

ε = 25.5

ε = 10000

10000

ε / M cm

-1

-1

30 20

-1

-1

precluded, but will spontaneously be oxidised by air to the manganese (III,IV) dimer: [Mn(cyclam)O]23+ or to hydrated MnO2 within a few hours in neutral or weakly basic solutions. With ligands unstable in acidic solutions, e.g., ONO
, the reaction must be performed in neutral solution and the product should be precipitated relatively quickly. Unfortunately, it has proven impossible to achieve yields of 1 from the triflate salt of the Mn(III,IV) dimer of more than 50%. Apparently, only one of the manganese ions in the Mn(III,IV) dimer is recovered as 1. The existence of 2 is surprising considering the fact that we have a reducing ligand coordinated to manganese in a relatively high oxidation state. Apparently, cyclam stabilises high oxidation states for manganese, which is also supported by the existence of a simple manganese (IV) cyclam complex: trans-[Mn(cyclam)F2](CF3SO3)2 [22]. 2 is apparently only stable in the solid state and is only formed because of its low solubility. No free iodine has been observed at any time working with this complex. Only a few other manganese (III) iodide complexes have been structurally characterised: [Mn(tpp)I] [7a] (tpp is tetraphenylporphyrin), [Mn{(CH3)3P}I3] [7b] and [Mn{C6H5C(NSi(CH3)3)2}I] [7c] all of which are five-coordinated and none of them containing simple amine ligands in addition to the iodide as is the case for 2. Acidic aqueous solutions of nitrite are not stable since nitrous acid will decompose to NO and NO2. Therefore, 3 is synthesised in neutral solution with stoichiometric amounts of 1 and sodium nitrite and the product is precipitated quickly with sodium perchlorate. If the solution is left too long, the green colour darkens and gas evolution is observed. Addition of an excess of perchlorate ions to an aqueous solution of 1 results in precipitation of a violet compound analysing as trans-[Mn(cyclam)(OH2)2](ClO4)3. However, this product loses the coordinated water thereby turning into 4. The loss and uptake of water is easy and the colour of the powder depends upon the humidity of the air. 4 is therefore best stored in a dry atmosphere. Perchlorate is normally considered a noncoordinating anion and it is surprising that it is able to compete with water. The reason for this being possible must be the negative charge on the perchlorate ion combined with the stability of the crystal structure of 4 compared to the stability of the yet unknown structure of trans-[Mn(cyclam)(OH2)2](ClO4)3. An aqueous solution of 5 reacts acidic confirming the proton on the coordinated acetic acid.

ε / M cm

1100

5000

10 0 10000

20000

30000-1 40000 E / cm

0 50000

Fig. 1. Absorption spectra of 1. To the left is the spectrum of a 13 mM solution and to the right the spectrum of a 0.1 mM solution, both in 1 mM CF3SO3H in water. The inset shows the weak lines between 22 000 and 24 000 cm
1.

S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

1101

Table 2 ˚ ) for 1, 2, 3a, 3b, 4 and 5 Selected bond lengths (A 1

2

3a

3b

4

5

X

O

I

O

O

O

O

Mn–X

2.1927(12) 2.1810(12)

2.9416(2)

2.1753(14) 2.1976(13)

2.1798(13) 2.1982(12)

2.1909(9)

2.1566(15) 2.1563(15)

2.1340(16) 2.1495(16)

Mn–N

2.0283(13) 2.0398(12) 2.0388(13) 2.0400(13)

2.028(2)

2.0336(15) 2.0345(14) 2.0341(15) 2.0322(14)

2.0318(13) 2.0392(14) 2.0309(14) 2.0377(13)

2.0280(7)

2.0319(18) 2.0355(16) 2.0375(18) 2.0391(17)

2.0418(17) 2.0384(19) 2.0348(18) 2.0250(19)

is observed at 20 500 cm
1 and we expect it to be a d–d transition although the method does not permit us to determine the extinction coefficient. Charge-transfer transitions start at approximately 26 500 cm
1.

[Mn(cyclam)Br2]Br in 4 M aqueous solution of HCl and HBr, respectively. The spectrum of 3 in acetonitrile (not shown) exhibits a very broad band at approximately 11 000 cm
1 (e = 12 M
1 cm
1), a sharper d–d absorption band (e = 17 M
1 cm
1) at 20 000 cm
1 and a charge-transfer transition (e = 1100 M
1 cm
1) at 28 000 cm
1. Additional intense charge-transfer bands are found at higher energies. The spectrum of 5 in acetonitrile (not shown) has a d–d transition (e = 14 M
1 cm
1) at 13 200 cm
1 and the first charge-transfer line (e = 4900 M
1 cm
1) is located at 26 700 cm
1. 2 and 4 apparently only exist in the solid state and, therefore, no solution spectra have been obtained. The solid state spectrum of 2 (not shown) obtained by transmission spectroscopy of a dispersion of a finely ground powder in poly(dimethylsiloxane) (12 500 cSt) shows a broad featureless transition starting at approximately 10 000 cm
1 and resulting in four broad bands between 23 000 and 46 000 cm
1. These lines we assign as charge-transfer transitions. Solid-state spectra of 4 were obtained by the same method. A band

4.1. Structural aspects All five complexes are high-spin and have the ground state configuration [Ar]3d4 for the central manganese, thus an axial elongation is anticipated for these complexes. ORTEP drawings of the cations with 50% probability ellipsoids showing the atom numbering schemes are given in Figs. 2–6. Hydrogens on carbon atoms have been omitted in all figures for clarity. Selected bond distances and angles are given in Table 2. The structures of the counter ions are well ordered and will not be described further. The cif files containing a full list of bond lengths, angles and torsion angles for all structures are found in the supplementary material. Weak hydrogen bonds linking the amine hydrogens and the counter ions are present in all six structures.

F41 O31 F33

C31

F43

F31

O32

C41

S3

C31

F32

F33

F42

F31

O32

O41

O43

S4

S3

O33

O51 O31

O42

F32 O1

O33

O2

Mn1

Mn2

C5

C15

N2

C1 C4

N1

N12

C11 C14

N11

C2 C3

C13

C12

Fig. 2. An ORTEP drawing of the two crystallographic independent cations of 1 showing the atom numbering scheme. The hydrogen bonds made by ˚. the cations are shown if the distance between donor and acceptor is below 3.1 A

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S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106 I1

O3 O2

Cl1

O1 Mn

C1

Mn

N

C1

C2

N1

C3

C3

C2

Fig. 3. An ORTEP drawing of the cation of 2 showing the atom numbering scheme.

 with two crystal1 crystallises in the space group P 1 lographically non-equivalent cations both located with the central Mn atom on an inversion centre. In both cations, the Mn is six-coordinate with the water molecules in the axial positions and cyclam occupying the four equatorial positions, see Fig. 2. The Mn–N bond lengths ˚ ), see Table 2, and signifiare all similar (2.028–2.040 A cantly shorter than the Mn–O bonds of 2.192(2) and ˚ resulting in slightly distorted tetragonally 2.181(2) A elongated octahedra. An extensive pattern of hydrogen bonds is present in the structure. The two non-equivalent cations participate in different hydrogen bond pattern. The water molecules coordinating to Mn1 make hydrogen bonds with O  O distances of 2.799(2) and ˚ to two triflate anions, see Fig. 2. The water 2.699(2) A molecules coordinating to Mn2 make one hydrogen ˚ ) to a triflate anion and one bond (O  O: 2.715(2) A ˚ ) to the water shorter hydrogen bond (O  O: 2.586(2) A of crystallisation. Two additional hydrogen bonds ˚ ) to triflate anions are (O  O: 2.796(2) and 2.751(2) A

3a

Fig. 5. An ORTEP drawing of the cation of 4 showing the atom numbering scheme.

made by the water of crystallisation (these bonds are not shown in Fig. 2). The different hydrogen bonding geometry is thought to be the reason for the difference in the Mn–O distances for the two crystallographically independent cations. 2 crystallises in the space group P42/m with Mn on a 2/m (C2h) site. I1 and C1 are located in the mirror plane and the twofold axis perpendicular to the mirror plane passes through Mn and the bond between the two carbon atoms in the five-membered ring, see Fig. 3. The counter ion is located on a 4 position. Thus, 2 is isostructural with trans-[Mn(cyclam)Br2]Br [2]. The six-coordinate manganese centre exhibits a strong tetragonal elongation with four equivalent Mn–N dis˚ and two equivalent Mn–I1 distances of 2.028(2) A ˚ , see Table 2. The distances from tances of 2.9416(2) A

3b N

N

O2

O2

O1

O1

C7

C8 C9

C6

Mn1

C5

N3

N4

Mn

C5

C1

N2 C4

N1 C3

C10 C1

N2 N1

C4

C2

C3

C2

O11 O12

N10

Fig. 4. An ORTEP drawing of one crystallographic independent cation of 3a and the unique cation of 3b showing the atom numbering scheme.

S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106 O22

C32 C31

O21

C28

N24

C29 C27

C30

N23

C21 Mn2

C26 N21

C25

C22

C24 N22 O23

C23

C33 O24

C12

C34

O2 C1

C11 C2

C10

O1

N1

N4

C3 C9

Mn1

C4

C8

N2

O3

C5 N3 C7

C13

C6 O4

C14

Fig. 6. An ORTEP drawing of the hydrogen bonded chain compound of 5 containing two crystallographically different cations. One inter˚ ) is shown. The molecular hydrogen bond (O24  O2 distance 2.421 A hydrogen atom in the O4–H  O22 hydrogen bond (not shown) is distributed over two sites of which only one is shown in the figure.

Mn to the axial iodides are very long but not longer than expected when extrapolated from the data for [Mn(cyclam)X2]+, where X = Cl [2,26], Br [2]. The increase in the Mn–X bond length upon varying X from Cl to Br ˚ , respectively and from Br to I is 0.16 and 0.253 A [2,26]; these two numbers compare well with the increase in the ionic radii of the halide ligands, being ˚ and r(I
)
r(Br
) = 0.24 A ˚ r(Br
)
r(Cl
) = 0.15 A [23]. We conclude that the variation in the manganese– halide bond lengths is caused mainly by the different ionic radii of the halide ions. 3 crystallises in two polymorphic forms. Thin plate crystals grew fast (3a) and needle shaped crystals grew slowly (3b). 3a crystallises in the space group P21/c with

1103

two crystallographically independent cations. The Mn atoms are each located on an inversion centre. 3b crystallises in the non-centrosymmetric space group P212121. Fig. 4 shows one cation of 3a and the unique cation of 3b. Both 3a and 3b are nitrito complexes, i.e., the NO2
ligand coordinates with an oxygen atom to Mn. This is expected since manganese (III) is normally considered a ‘‘hard’’ ion that prefers O over N donors. All three cations exhibit a tetragonally elongated six-coordinate Mn: The Mn–N distances are in the ˚ and the Mn–O distances are in range 2.031–2.038 A ˚ , see Table 2. The two O–N the range 2.175–2.198 A bonds in each nitrito ligands are not equal and the longest bond is found for the coordinating oxygen in all three cations: O(coordinating)–N is in the range 1.276– ˚ and the other O–N distance is in the range 1.288 A ˚ . The ligands are bent with an O–N–O an1.210–1.224 A ˚ . All three cations contain intramolecugle of 114.7(2) A lar hydrogen bonds, in which the non-coordinating oxygen of the ONO
ligand makes hydrogen bonds to the amine hydrogens resulting in six-membered rings: [Mn–O–N–O  H–N–], see Fig. 4. The hydrogen bond distances are collected in Table 3. For the Mn2 site of 3a, the ONO groups are directed between the two cyclam nitrogens of the six-membered ring. The same applies for one ONO group of 3b. The other ONO group of 3b and both ONO groups of the Mn1 site of 3a are directed towards one cyclam nitrogen resulting in a more asymmetric hydrogen bonding pattern. For the cation in 3a containing Mn2 and for both ONO groups in 3b, there is also an intermolecular hydrogen bond from the uncoordinated oxygen atom to cyclam in a neighbouring cation. 4 is isostructural with 2 having perchlorates on the same sites as iodine in 2. Cl1 and O1 of the coordinated perchlorate are located in the mirror plane. Cl2 of the perchlorate counter ion is located on a 4 site. Again, we have a tetragonally elongated complex as seen from Table 2. There is no doubt that we have two truly coordinating perchlorate ions in 4. The coordinating oxygen atom of the perchlorate ligand exhibits the largest O–Cl ˚ compared to O2– bond distance: O1–Cl1: 1.4747(9) A ˚ and O3–Cl1: 1.4193(9) A ˚ . This bond Cl1: 1.4256(10) A is also considerably longer than the unique value for ˚ . The Mn–O1– the perchlorate counter ion: 1.4415(7) A Cl1 angle is 154.29(7). 5 crystallises in the space group P21 with two formula units in the asymmetric unit. The Mn–N distances are in ˚ , see Table 2. The Mn–O disthe range 2.025–2.042 A ˚ and are considertances are in the range 2.134–2.157 A ably shorter than the axial Mn–O distances in 1, 3 and 4. The C–O bonds in acetate or acetic acid are in all four cases shorter for O coordinating to the manganese ˚ ) than the other C–O bonds (1.268– (1.237–1.261 A ˚ 1.290 A). The O–C–O angles are very close to 120 (119.5–121.8). The structure of 5 is chain-like where

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S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

Table 3 ˚ ) for 3a, 3b and 5 Selected hydrogen bond lengths (A 3a N1  O2 N2  O2a

2.963(2) 3.158(2)

N11  O12 N12  O12b N11  O12c

3.106(2) 3.144(2) 3.060(2)

3b N1  O2 N4  O2 N3  O2d

3.376(2)g 3.010(2) 3.081(2)

N2  O12 N3  O12 N1  O12e

3.190(2) 2.993(2) 2.889(2)

5 O24  O2 O4  O22f

2.433(2) 2.421(2)

N4  O2 N2  O4 N24  O22 N22  O24

2.913(2) 2.914(2) 2.866(3) 2.874(3)

a b c d e f g

2
x, 1
y, 1
z. 1
x, 2
y, 1
z. 1
x, 3
y, 1
z. x, y
1, z. x, 1 + y, z. x
1, y, z
1. This is considered a very weak bond, but has been included for reference.

the coordinating acetic acid makes a very short hydrogen bond to the acetate coordinating to the next manganese centre in the chain. The O  O distances are ˚ , which are of the same magni2.421(2) and 2.433(2) A tude as intramolecular hydrogen bonds in monohydrogen dicarboxylates such as hydrogen phthalate ˚ in Mg(CH3OH)6H phthalate H2O) [27a] or (2.378(2) A ˚ for the hydrogen maleate (2.4214(5) and 2.4218(5) A two hydrogen maleate ions in methylammonium hydrogen maleate) [27b]. Though most often seen as intramolecular hydrogen bonds, very short and strong intermolecular hydrogen bonds can also be observed, e.g., in hydrogen succinate [27c]. These are considered among the strongest O–H  O bonds known. For comparison, the value for sodium hydrogen diacetate is ˚ [28]. The hydrogen atom in one of the short 2.474 A ˚ ) is disordered bonds (O24–H  O2, distance 2.433(2) A between two sites each with a population of 0.50(4), while the other (O4–H  O22) is localised. A similar complex: trans-[Co(en)2(CH3COO)(CH3COOH)](ClO4)2 Æ H2O [29] (en is 1,2-ethanediammine) also exhibits chains with very short hydrogen bonds (2.442(10) and 2.370(10) ˚ ), but no other analogues have been structurally charA acterised [30]. The non-coordinating oxygen atoms of both acetate and acetic acid also make intramolecular hydrogen bonds to one NH group of the cyclam ligand, the values are collected in Table 3. 4.2. Structural comparisons 4.2.1. Cyclam complexes In all four structures, the cyclam ligand adopts the energetically most favourable conformation denoted as trans-III [31]. The bond lengths and bond angles within

the cyclam ligand are very similar for 1, 2, 3a, 3b, 4 and 5 and do not deviate from those found in other trans-cyclam complexes. The bond lengths and bond angles involving the central manganese and the cyclam nitrogens are similar and do not vary even when the central manganese ion has a different spin state [6] or oxidation state (IV or V) [22,4] The average equatorial bond distances Mn–N for both new and previously known MnIII(cyclam) complexes are listed in Table 4. The val˚ . For the N–Mn–N ues in all complexes are 2.03 ± 0.01 A bond angles, the values are 94 ± 1 for the six-membered ring and 86 ± 1 for the five-membered ring. This induces a deviation from tetragonal symmetry of the coordination sphere for all complexes in Table 4. The axial Mn–X distances vary widely with X, see fourth column of Table 4. For the high-spin complexes, the axial bonds are significantly longer than the equatorial Mn–N bonds. The longest and shortest Mn–X bond lengths are found for the iodo and the cyanato complexes, respectively. The complexes have been ordered after decreasing Mn–X bond lengths. A glance at Table 4 reveals a concomitant grouping of compexes with the same coordination sphere with the notable exception of 5. The axial bond length decreases when the donor atom changes from halogen via oxygen to nitrogen. The reason for the relative short axial distances in 5 is thought to be the chain-like structure; comparable or shorter bond lengths are found for the true chain structures [Mn(cyclam)(SO4)]ClO4 Æ H2O (average Mn–O ˚ ) and [Mn(cyclam)(HCOO)](ClO4)distance 2.143 A ˚ ) [32]. The cyano (CF3SO3) (Mn–O distance 2.1051(8) A complex is low-spin and exhibits a slight tetragonal compression: The axial distances are shorter than the equatorial distances in this complex.

S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

1105

Table 4 Comparison of structural data for Mn(III) cyclam complexes Complex

Spin state

Ligating atoms

Average Mn–X ˚) (A

Average Mn–Ncyclam s () ˚) (A

Colour

Reference

2 trans-[Mn(cyclam)I2]+ trans-[Mn(cyclam)Br2]+ trans-[Mn(cyclam)Cl2]+ trans-[Mn(cyclam)(ONO2)2]+

hs hs hs hs

4N, 4N, 4N, 4N,

2I 2Br 2Cl 2O

2.9416(2) 2.689(1) 2.527(1) 2.221(4)

2.028(2) 2.029(6) 2.035(3) 2.036(7)

dark red green green blue

this work [2] [2,26] [2]

4 trans-[Mn(cyclam)(OClO3)2]+

hs

4N, 2O

2.1909(9)

2.0280(7)

red

this work

3 trans-[Mn(cyclam)(ONO)2]+

hs

4N, 2O

2.188(12)

2.034(3)


5.9a

yellow

this work

3+

hs hs hs

4N, 2O 6N 6N

2.187(8) 2.175(3) 2.166(17)

2.037(6) 2.041(3) 2.038(4)

7.8 3.76 1.48

violet orange brown

this work [4] [2]

hs hs ls

4N, 2O 6N 4N, 2C

2.149(9) 2.148(4) 2.007(4)

2.036(5) 2.043(4) 2.029(4)


4.84 1.40 1.3

blue yellow–green yellow

this work [5] [6]

1 trans-[Mn(cyclam)(OH2)2] trans-[Mn(cyclam)(N3)2]+ trans-[Mn(cyclam)(NCS)2]+

5 trans-[Mn(cyclam)(Ac)(HAc)]2+ trans-[Mn(cyclam)(NCO)2]+ trans-[Mn(cyclam)(CN)2]+

3.71 3.28 2.50
4.49 8.71

Note that when using this table the values from [2,26] have been obtained at room temperature. Ac and HAc are short terms for acetate and acetic acid, respectively. Mn–Ncyclam denotes the four equatorial bond distances from the central manganese to cyclam and Mn–X denotes the two axial distances from the central manganese to the trans ligands. The complexes are ordered after the value of Mn–X. The uncertainties are given as root mean square deviations (rmsd). If only a single parameter is available or if the standard uncertainty (su) is larger, the su is given. The tilt angle, s, is defined in Fig. 7. For complexes containing an inversion centre, MnN4 lies in a well-defined plane. For the remaining: 3b, 5, trans-[Mn(cyclam)(CN)2]+ and trans-[Mn(cyclam)(NCO)2]+, a least-squares plane was used. a Average value for 3a and 3b.

N

(b) X

O

O H N

N H

H N

N H

O

X

N

4.2.2. Tilt angles In the following, we explore the tilt angle s, see Fig. 7, of the axial Mn–X bond with respect to the normal to the plane defined by the central manganese and the four cyclam nitrogens. In all twelve complexes in Table 4, the Mn–X bond is tilting towards a six-membered ring. The values are collected in Table 4. For the majority of the complexes, the tilt is directed between the two nitrogens having hydrogens pointing in the same direction as the Mn–X bond, see Fig. 7(a). For three complexes: 3 (both a and b), trans-[Mn(cyclam)(ONO2)2]+ and 5 the tilt is directed in the opposite direction, see Fig. 7(b).

(a)

O

Notice the variety of colours of [Mn(cyclam)(ONO2)2]NO3, 4, 3, 1 and 5, which all have axial oxygen donors, see Table 4. Two factors determine the colours of these complexes: The position of the weak (12 < e < 25 M
1 cm
1) d–d transitions (4: 20 500 cm
1, 3: 20 000 and 11 000 cm
1, 1: 17 360 cm
1, and 5: 13 200 cm
1), and the position of the charge-transfer cut-off, which occurs at lower energies for 5 and 3 (23 000 and 24 000 cm
1) than for 1 (25 000 cm
1) and 4 (26 500 cm
1). Since the cyclam ligand coordinates in the same way in all the complexes, the differences must originate in the axial ligands. These all have the same donor atom but behave differently as p-donors and have different redox properties. An attempt to explain the electronic structure of these complexes in terms of density functional calculations is ongoing. Especially, the position of the 5B1 ! 5A1 transition for 1 is very high in energy compared to what is expected from using the spectrochemical series [23].

Fig. 7. A schematical drawing of the definition of the tilt angle, s is defined as the angle between the normal to the MnN4 plane and the Mn–X bond. (a) The positive tilt angle for X = I, Br, Cl, OH2, OClO3, N3, NCS, NCO and CN; (b) the negative tilt angle for X = ONO, ONO2 and CH3COOH/CH3COO exemplified by X = ONO. Intramolecular hydrogen bonds from NH on cyclam to a non-coordinating oxygen atom in the ligand are present in these complexes.

These are marked with a negative tilt-angle in Table 4. The tilt represented in Fig. 7(a) has been rationalised in terms of the repulsion between the bonding orbitals between Mn and the axial ligands and the donor orbitals on nitrogen that are slightly misdirected due to the steric restraints of the cyclam ring [33]. The explanation for the exceptions in Fig. 7(b) is thought to be the six-membered intramolecular hydrogen bonds present in these complexes and none of the others. 4.2.3. Mn(III) perchlorato complexes No other manganese complexes having two coordinating perchlorate ions have been structurally characterised [30]. The corresponding Mn–O distances for the previously known six-coordinate complexes are in the

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S. Mossin et al. / Inorganica Chimica Acta 358 (2005) 1096–1106

˚ [34–37] and thus considerably longer range 2.33–2.52 A ˚ found in 4. This value is more than the value 2.1909(9) A comparable to the one found in a five-coordinate com˚ [38]. The Mn–O–Cl angles for the previplex: 2.183 A ously characterised complexes are found in the interval 127–142 compared to the value 154.29(7) for 4. Thus, in 4 we find a more linear coordination mode.

Acknowledgement The authors thank Flemming Hansen, Centre for Crystallographic Studies, University of Copenhagen for obtaining the crystallographic data; Solveig Kallesøe, University of Copenhagen for obtaining magnetic susceptibility data; Karen Jørgensen and Karin Linthoe, University of Copenhagen for performing elemental analyses.

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.ica.2004.10.005.

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