Bis­(guanidinium) bis­(oxalato)­platinate(II)

The title compound, (CH₆N₃)₂[Pt(C₂O₄)₂] or (guanidinium)₂[Pt(ox)₂] (ox = oxalate), possesses an intriguing three-dimensional hydrogen-bonding network in the crystal structure, where extensive hydrogen bonds are formed between N—H(guanid­inium) units and O atoms of oxalates [N...O = 2.913 (5)–3.197 (5) Å]. The [Pt(ox)₂]²⁻ anions stack weakly in a one-dimensional manner, with an intermolecular Pt...Pt distance of 3.5876 (7) Å. The Pt atom is located at an inversion centre.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.014
• wR factor = 0.034
• Data-to-parameter ratio = 9.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



THETM_01  Alert B The value of sine(theta_max)/wavelength is less than 0.575
          Calculated sin(theta_max)/wavelength =    0.5554


 Alert Level C:



REFNR_01  Alert C Ratio of reflections to parameters is < 10 for a
          centrosymmetric structure
          sine(theta)/lambda                0.5554
          Proportion of unique data used    1.0000
          Ratio reflections to parameters   9.3918

PLAT_369  Alert C Long   C(sp2)-C(sp2) Bond  C(2)   -   C(3)   =       1.55 Ang.

General Notes



ABSTM_02  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.288     0.675
          Tmin and Tmax expected:      0.212     0.645
          RR =      1.300
          Please check that your absorption correction is appropriate.


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 2 Alert Level C = Please check

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S1. Comment

We have been for a long time interested in the one-dimensional systems consisting of dimers doubly bridged with amidate or carboxylate ligands (see for example in Sakai, Tanaka et al., 1998; Sakai, Takeshita et al., 1998; Sakai et al., 2002). All the dimers used so far have been cationic dimers with a general formula of [Pt₂L₄(µ-bridge)₂]²⁺ [L₂ = (NH₃)₂, ethylenediamine, 2,2'-bipyridine, 1,10-phenanthroline, etc.; bridge = acetamidate, pivalamidate, acetate, benzoate, etc.]. In this context, attempts have been made to prepare a Pt(ox) dimer doubly bridged by guanidinate ligands, [Pt₂(ox)₂(µ-guanidinato)₂]²⁻. However, the preparation of such anionic dimers have been unsuccessful so far. Here we report on the crystal structure of the title compound, which was obtained as a by-product in these studies.

The asymmetric unit of (I) consists of a half unit of the formula (Fig. 1). The Pt ion is located at an inversion centre and therefore the coordination around it has a crystallographically planar geometry. The [Pt(ox)₂]²⁻ anion possesses a distorted square-planar stereochemistry due to the structural restraint arising from the oxalate chelates (see Table 1).

As shown in Fig. 2, the crystal packing of (I) is stabilized with extensive hydrogen bonds formed between guanidinium cations and oxygen atoms of oxalates (see also Table 2). Fig. 2(b) shows that the [Pt(ox)₂]²⁻ anions stack along the a axis, where the Pt1—Pt1ⁱ vector is canted by 21.9° with respect to the orthogonal vector of the best plane defined by the four coordinated oxygen atoms. The intermolecular Pt—Pt distance [3.5876 (7) Å] is much longer than those reported for partially oxidized analogs (Pt—Pt = 2.717–2.876 Å; Miller, 1982), consistent with our assignment that (I) has an oxidation level of Pt^II. However, the deep green color of (I) implies that metal-metal interactions are to some extent promoted in (I). Examples of non-partially oxidized compounds are as follows: K₂[Pt(ox)₂]·2H₂O (Pt—Pt > 8 Å, Mattes & Krogmann, 1964; [Cu(en)₂][Pt(ox)₂] (Pt—Pt = 3.554 and 3.855 Å, Bekaroglu et al., 1976; Ca[Pt(ox)₂]·3.5H₂O (Pt—Pt = 3.18 Å, Krogmann, 1968).

S2. Experimental

A solution of K₂[Pt(ox)₂]·2H₂O (0.20 mmol, 0.098 g; Werner & Grebe, 1899) and guanidine carbonate (0.20 mmol, 0.024 g) in water (5 ml) was refluxed for 3 h, during which the solution became dark green and a small amount of black precipitate deposited. The solution was then filtered while it is hot. Leaving of the filtrate at room temperature overnight afforded (I) as dark-green needles, which were collected by filtration and air-dried (yield: 30%). Analysis calculated for C₁₂H₆N₆O₈Pt: C 14.86, H 2.31, N 16.97%; found: C 14.67, H 2.46, N 17.11%.

S3. Refinement

All H atoms of the guanidinium ion were located at their idealized positions as riding atoms (N—H = 0.86 Å).

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: KENX (Sakai, 2002); software used to prepare material for publication: SHELXL97, TEXSAN (Molecular Structure Corporation, 1999), KENX and ORTEPII (Johnson, 1976).

Figures

	Fig. 1. The structure of (I), showing the atom-labeling scheme. Displacement ellipsoids are shown at the 50% probability level.
	Fig. 2. Crystal packing view of (I) showing a hydrogen-bonding network: (a) along the a axis and (b) along the c axis.

cis-Diammine(L-pyrolglutamato)platinum(II)

Crystal data

(CH6N3)2[Pt(C2O4)2]	F(000) = 464.0
Mr = 491.31	? # Insert any comments here.
Monoclinic, P21/c	Dx = 2.540 Mg m^−3
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 3.5876 (7) Å	Cell parameters from 1567 reflections
b = 14.684 (3) Å	θ = 2.8–23.3°
c = 12.237 (2) Å	µ = 10.97 mm^−1
β = 94.686 (3)°	T = 296 K
V = 642.5 (2) Å^3	Prism, dark green
Z = 2	0.15 × 0.15 × 0.04 mm

Data collection

Bruker SMART APEX CCD detector diffractometer	911 independent reflections
Radiation source: fine-focus sealed tube	685 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.033
Detector resolution: 8.366 pixels mm^-1	θmax = 23.3°, θmin = 2.8°
ω scans	h = −3→3
Absorption correction: gaussian (XPREP in SAINT; Bruker, 2001)	k = −15→16
Tmin = 0.288, Tmax = 0.675	l = −12→13
2782 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.015	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.034	H-atom parameters constrained
S = 0.94	w = 1/[σ^2(Fo^2) + (0.0131P)^2] where P = (Fo^2 + 2Fc^2)/3
911 reflections	(Δ/σ)max = 0.001
97 parameters	Δρmax = 0.44 e Å^−3
0 restraints	Δρmin = −0.43 e Å^−3

Special details

Experimental. The first 50 frames were rescanned at the end of data collection to evaluate any possible decay phenomenon. Since it was judged to be negligible, no decay correction was applied to the data.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Mean-plane data from final SHELXL refinement run:-

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

3.3268 (0.0024) x + 4.7558 (0.0244) y + 1.3607 (0.0172) z = 3.0583 (0.0148)

* 0.0000 (0.0000) O1 * 0.0000 (0.0001) O2 * 0.0000 (0.0001) O1_$2 * 0.0000 (0.0000) O2_$2 0.0000 (0.0000) Pt1

Rms deviation of fitted atoms = 0.0000

3.2482 (0.0037) x + 3.0863 (0.0327) y + 3.5940 (0.0287) z = 4.2660 (0.0135)

Angle to previous plane (with approximate e.s.d.) = 12.35 (0.19)

* −0.0045 (0.0034) C1 * 0.0015 (0.0011) N1 * 0.0015 (0.0012) N2 * 0.0015 (0.0011) N3

Rms deviation of fitted atoms = 0.0026

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Pt1	0.0000	0.5000	0.5000	0.02899 (10)
O1	0.1511 (8)	0.4323 (2)	0.3672 (2)	0.0361 (8)
O2	−0.0992 (9)	0.60076 (19)	0.3904 (2)	0.0397 (8)
O3	0.2738 (10)	0.4599 (2)	0.1954 (3)	0.0502 (9)
O4	0.0174 (9)	0.6367 (2)	0.2205 (2)	0.0471 (9)
N1	0.6649 (11)	0.1083 (2)	0.4934 (3)	0.0384 (9)
H1A	0.7498	0.0925	0.4325	0.046*
H1B	0.6451	0.0686	0.5443	0.046*
N3	0.4398 (10)	0.2171 (2)	0.6035 (3)	0.0434 (10)
H3A	0.3770	0.2726	0.6148	0.052*
H3B	0.4212	0.1768	0.6538	0.052*
N2	0.5943 (11)	0.2548 (3)	0.4314 (3)	0.0442 (10)
H2A	0.5320	0.3105	0.4422	0.053*
H2B	0.6760	0.2392	0.3700	0.053*
C1	0.5648 (11)	0.1937 (3)	0.5089 (4)	0.0324 (11)
C2	0.1621 (13)	0.4837 (3)	0.2827 (4)	0.0343 (12)
C3	0.0176 (13)	0.5823 (3)	0.2962 (4)	0.0359 (12)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pt1	0.03635 (16)	0.02617 (15)	0.02489 (15)	0.00196 (14)	0.00518 (10)	−0.00056 (12)
O1	0.053 (2)	0.0300 (19)	0.0264 (18)	0.0062 (15)	0.0094 (15)	−0.0006 (15)
O2	0.061 (2)	0.0315 (18)	0.0277 (18)	0.0110 (16)	0.0097 (16)	0.0019 (14)
O3	0.071 (3)	0.050 (2)	0.032 (2)	0.0020 (19)	0.0212 (19)	−0.0074 (16)
O4	0.065 (2)	0.045 (2)	0.033 (2)	0.0039 (17)	0.0105 (17)	0.0096 (16)
N1	0.058 (2)	0.032 (2)	0.028 (2)	0.008 (2)	0.0133 (18)	0.0016 (17)
N3	0.055 (3)	0.032 (2)	0.045 (3)	0.002 (2)	0.014 (2)	−0.0060 (19)
N2	0.058 (3)	0.029 (2)	0.047 (3)	0.003 (2)	0.010 (2)	0.003 (2)
C1	0.027 (3)	0.029 (3)	0.041 (3)	−0.001 (2)	−0.001 (2)	−0.004 (2)
C2	0.031 (3)	0.040 (4)	0.031 (3)	−0.003 (2)	0.001 (2)	−0.005 (2)
C3	0.037 (3)	0.034 (3)	0.037 (3)	−0.004 (2)	0.005 (2)	−0.002 (2)

Geometric parameters (Å, º)

Pt1—O1	2.016 (3)	N1—C1	1.322 (5)
Pt1—O2	2.009 (3)	N1—H1A	0.8600
Pt1—Pt1^i	3.5876 (7)	N1—H1B	0.8600
Pt1—O2^ii	2.009 (3)	N3—C1	1.321 (5)
Pt1—O2^ii	2.009 (3)	N3—H3A	0.8600
Pt1—O1^ii	2.016 (3)	N3—H3B	0.8600
O1—C2	1.284 (5)	N2—C1	1.316 (5)
O2—C3	1.287 (5)	N2—H2A	0.8600
O3—C2	1.222 (5)	N2—H2B	0.8600
O4—C3	1.223 (5)	C2—C3	1.551 (6)
O2—Pt1—O1	82.52 (12)	C1—N1—H1B	120.0
O2^ii—Pt1—O1	97.48 (12)	H1A—N1—H1B	120.0
O1^ii—Pt1—O2	97.48 (12)	C1—N3—H3A	120.0
O2^ii—Pt1—O2^ii	0.00 (11)	C1—N3—H3B	120.0
O2^ii—Pt1—O2	180.000 (1)	H3A—N3—H3B	120.0
O2^ii—Pt1—O2	180.000 (1)	C1—N2—H2A	120.0
O2^ii—Pt1—O1^ii	82.52 (12)	C1—N2—H2B	120.0
O2^ii—Pt1—O1^ii	82.52 (12)	H2A—N2—H2B	120.0
O2—Pt1—O1^ii	97.48 (12)	N2—C1—N3	120.5 (4)
O1—Pt1—O1^ii	180.00 (9)	N2—C1—N1	120.3 (4)
O2^ii—Pt1—Pt1^i	82.96 (9)	N3—C1—N1	119.2 (4)
O2^ii—Pt1—Pt1^i	82.96 (9)	O3—C2—O1	124.7 (4)
O2—Pt1—Pt1^i	97.04 (9)	O3—C2—C3	119.8 (4)
O1—Pt1—Pt1^i	70.45 (9)	O1—C2—C3	115.5 (4)
O1^ii—Pt1—Pt1^i	109.55 (9)	O4—C3—O2	124.1 (4)
C2—O1—Pt1	112.8 (3)	O4—C3—C2	120.5 (4)
C3—O2—Pt1	113.0 (3)	O2—C3—C2	115.4 (4)
C1—N1—H1A	120.0
O3—C2—C3—O4	−0.6 (7)	O3—C2—C3—O2	179.0 (4)
O1—C2—C3—O4	179.8 (4)	O1—C2—C3—O2	−0.5 (6)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O1	0.86	2.39	3.120 (5)	143
N1—H1A···O3^iii	0.86	2.49	3.197 (5)	139
N1—H1A···O4^iii	0.86	2.21	2.969 (4)	147
N2—H2B···O4^iii	0.86	2.21	2.971 (5)	147
N1—H1B···O3^iv	0.86	2.40	3.106 (5)	139
N3—H3B···O3^iv	0.86	2.15	2.913 (5)	148
N3—H3A···O2^ii	0.86	2.11	2.944 (5)	164

Symmetry codes: (ii) −x, −y+1, −z+1; (iii) −x+1, y−1/2, −z+1/2; (iv) x, −y+1/2, z+1/2.