fac-{2-[Bis(2-amino­eth­yl)amino]­ethanaminium}trichloridorhodium(III) chloride hemihydrate

Barbara Kutzky; Christian Neis; Kaspar Hegetschweiler

doi:10.1107/S1600536810051846

. 2010 Dec 18;67(Pt 1):m92–m93. doi: 10.1107/S1600536810051846

fac-{2-[Bis(2-aminoethyl)amino]ethanaminium}trichloridorhodium(III) chloride hemihydrate

Barbara Kutzky ^a, Christian Neis ^a, Kaspar Hegetschweiler ^a,^*

PMCID: PMC3050386 PMID: 21522607

Abstract

The crystal structure of the title compound, [Rh(C₆H₁₉N₄)Cl₃]Cl·0.5H₂O, is isotypic with the previously reported Ru analogue. The structure contains two crystallographically independent [Rh(Htren)Cl₃]⁺ cations with a facial tridentate coordination of the monoprotonated tren ligand [tren = tris(2-aminoethyl)amine], leading to an overall distorted octahedral coordination environment around the Rh(III) atom. In one of the two cations, the ethylene groups of the two chelate rings as well as the non-coordinating ethylammonium group are disordered over two sets of sites [0.579 (3):0.421 (3) occupancy ratio]. A series of N—H⋯Cl and O—H⋯Cl hydrogen bonds stabilizes the structure.

Related literature

The preparation of the title compound has been described by Hyvärinen et al. (2009 ▶) and the crystal structure of the isotypic Ru^III complex has been reported by Sakai et al. (1996 ▶). Disorder phenomena, caused by a superposition of differently folded chelate rings of the tren ligand have been observed by Düpre et al. (1999 ▶). Hypodentate coordination of polyamine ligands has been discussed by Blackman (2005 ▶) and Neis et al. (2010 ▶). For disorder phenomena, see: Hirshfeld (1976 ▶).

Experimental

Crystal data

[Rh(C₆H₁₉N₄)Cl₃]Cl·0.5H₂O
M _r = 400.97
Monoclinic,
a = 13.8022 (6) Å
b = 14.1954 (5) Å
c = 13.6208 (5) Å
β = 91.196 (1)°
V = 2668.11 (18) Å³
Z = 8
Mo Kα radiation
μ = 2.06 mm⁻¹
T = 100 K
0.15 × 0.05 × 0.03 mm

Data collection

Bruker X8 APEX KappaCCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2010 ▶) T _min = 0.747, T _max = 0.941
56384 measured reflections
13775 independent reflections
13026 reflections with I > 2σ(I)
R _int = 0.036

Refinement

R[F ² > 2σ(F ²)] = 0.025
wR(F ²) = 0.065
S = 1.18
13775 reflections
328 parameters
2 restraints
H-atom parameters constrained
Δρ_max = 1.79 e Å⁻³
Δρ_min = −1.89 e Å⁻³

Data collection: APEX2 (Bruker, 2010 ▶); cell refinement: SAINT (Bruker, 2010 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2010 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810051846/si2315sup1.cif

e-67-00m92-sup1.cif^{(31.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810051846/si2315Isup2.hkl

e-67-00m92-Isup2.hkl^{(673.4KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Rh2—N6	2.0389 (12)
Rh2—N5	2.0510 (12)
Rh2—N7	2.0964 (12)
Rh2—Cl4	2.3522 (3)
Rh2—Cl6	2.3731 (3)
Rh2—Cl5	2.3735 (3)
Rh1—N2	2.0402 (11)
Rh1—N3	2.0420 (11)
Rh1—N1	2.0820 (11)
Rh1—Cl1	2.3626 (3)
Rh1—Cl3	2.3652 (3)
Rh1—Cl2	2.3718 (3)

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Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N3—H3B⋯Cl7ⁱ	0.92	2.42	3.2560 (13)	150
N3—H3A⋯Cl4ⁱ	0.92	2.47	3.3279 (12)	155
N2—H2B⋯Cl7ⁱ	0.92	2.34	3.1744 (12)	151
N5—H5D⋯Cl8	0.92	2.45	3.3452 (13)	166
N4—H4A⋯Cl8ⁱⁱ	0.91	2.26	3.1322 (13)	161
N5—H5C⋯Cl4ⁱⁱⁱ	0.92	2.75	3.5319 (12)	143
N6—H6D⋯Cl1^iv	0.92	2.62	3.4354 (13)	148
N4—H4C⋯Cl6^v	0.91	2.35	3.1729 (13)	150
N81—H81B⋯Cl7^vi	0.91	2.24	3.109 (14)	159
O1W—H1WA⋯Cl7^vii	0.86	2.25	3.0797 (15)	163
N2—H2A⋯Cl1^viii	0.92	2.62	3.4348 (12)	148
N6—H6C⋯Cl8	0.92	2.36	3.2199 (13)	156

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) ; (viii) .

Acknowledgments

We thank Dr Volker Huch (Universität des Saarlandes) for the data collection.

supplementary crystallographic information

Comment

The title compound has recently been obtained as a byproduct in the synthesis of [RhCl₂(tren)]⁺. Based on the slightly longer wave lengths of the d-d transitions, a partial coordination of the tren ligand was assigned to [RhCl₃(Htren)]⁺. Considering a step by step binding of the nitrogen donors to a mononuclear aqua-chlorido-Rh^III precursor, such an intermediate with three coordinated amino groups could either have a meridional or a facial geometry. The two forms cannot be distinguished by NMR spectroscopy, because both diastereomers exhibit C_s symmetry for the averaged solution structure.

The crystal structure analysis confirmed tridentate binding for the Htren⁺ ligand and exhibited a facial geometry for the coordinated diethylenetriamine unit (Fig. 1). Partial metal binding ("hypodentate coordination") of polyamine ligands is well known. Hypodentate coordination can either be caused by the specific steric requirements of the ligand or by slow ligand substitution. The observation, that vigorous conditions in the synthetic procedure resulted in an exclusive formation of [RhCl₂(tren)]⁺ indicates that the incompletely coordinated ligand of the title compound is due to kinetic rather than thermodynamic reasons. [RhCl₃(Htren)]⁺ should thus be regarded as an intermediate, trapped on its way to [RhCl₂(tren)]⁺.

The structure of the title compound is isotypic with the previously reported Ru analogue. The asymmetric unit contains two crystallographically independent [RhCl₃(Htren)]⁺ cations, two crystallographically independent chloride anions and one water molecule. The entire structure is stabilized by a three dimensional network of hydrogen bonds (Table 2). Notably, one of the hydrogen atoms of the water molecule (H1WB) has no acceptor: its nearest neighbors are the hydrogen atoms of an ethylenediamine group. Two coordinated chloride ions (Cl2 and Cl3) already exhibit O···Cl separations of 3.675 and 3.784 Å. The molecular structure of one of the cations closely approaches C_s symmetry with the two chelate rings having a λ and δ conformation. The second cation exhibited some disorder for the five membered Rh—N—C—C—N rings and the non coordinating ethylammonium group. This disorder could be resolved and has been refined as a superposition of two distinct conformers. Within one particular form, the same type of conformation (i.e.λ/λ or δ/δ) was observed for the two chelate rings.

In comparison to the isotypic Ru complex, the M—N and M—Cl bonds of the title compound are, as expected, slightly shorter. In both congeners, the M—N bonds of the tertiary nitrogen atoms were slightly longer. In addition, a trans influence (push-pull mechanism) has found to be operative (Table 1). However, for the Ru congener, these effects were - if at all - barely significant. This is now different for the title compound, where the accuracy of the structure has been increased by almost one order of magnitude.

Experimental

Orange crystals of the title compound were grown from aqueous 1 mol/L HCl. ¹H-NMR (D₂O): δ (p.p.m.) = 3.06 (2H), 3.20 (4H), 3.35 (2H), 3.60 (2H), 3.91 (2H), 5.52 (broad, 2NH), 5.62 (broad, 2NH). ¹³C-NMR (D₂O): δ (p.p.m.)= 35.1, 46.1, 59.6, 62.2. UV/Vis (H₂O) λ_max (nm) = 396, 313.