cis-(Cyclo­butane-1,1-dicarboxyl­ato)­bis­(2-methyl­pyridine)platinum(II)

The asymmetric unit in the title compound, [Pt(C₆H₆O₄)(C₆H₇N)₂], is composed of one-half of a mol­ecule. The complex lies on a mirror plane which contains the Pt atom and three C atoms of the cyclo­butane group, the fourth C atom being disordered with respect to the mirror plane. The Pt^II ion is tetra­coordinated in a square-planar environment.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.004 Å
• Disorder in main residue
• R factor = 0.017
• wR factor = 0.044
• Data-to-parameter ratio = 18.2

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT241_ALERT_2_B Check High      Ueq as Compared to Neighbors for        C10

Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.98
PLAT220_ALERT_2_C Large Non-Solvent    C     Ueq(max)/Ueq(min) ...       2.57 Ratio
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        C11
PLAT301_ALERT_3_C Main Residue  Disorder .........................       4.00 Perc.
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.11 Ratio
PLAT779_ALERT_2_C Suspect or Irrelevant (Bond) Angle in CIF ......      32.20 Deg.
              C10  -C9   -C10     7.575   1.555   1.555
PLAT779_ALERT_2_C Suspect or Irrelevant (Bond) Angle in CIF ......      31.80 Deg.
              C10  -C11  -C10     7.575   1.555   1.555

Alert level G
ABSTM02_ALERT_3_G  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
            Tmin and Tmax reported:      0.237     0.455
            Tmin and Tmax expected:      0.146     0.393
            RR =      1.397
            Please check that your absorption correction is appropriate.
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          2

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   7 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   5 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Cis-diammine(1,1-cyclobutanedicarboxylato) platinum(II) (Carboplatin) is commonly used for the treatment of testicular and overian cancer as well as cervical, bladder and head and neck tumors. It has proven to be the only second-generation platinum complex commercially available worldwide at present (Jakuper et al., 2003). But the application of Carboplatin in therapy is limited by the dose-dependent nephrotoxicity and other side effects. Therefore, the search for the new potent platinum complexes possessing high antitumor activity and lack of cross-resistance is needed. The title compound is a new soluble carboplatin analogue containing an asymmetric chelating malonate anion as its carrier and anticancer tests are presently being carried out.

The asymmetric unit in the title compound, C₁₈H₂₀N₂O₄Pt,is composed of half a molecule (Fig. 1). Indeed the complex is distributed around a mirror plane which contains the Platinum and the C8, C9 and C11 atoms of the cyclobutane group, the fourth one, C10, is disordered with respect to the mirror plane. The Pt atom is coordinated in a square-pyramidal enironment (Fig. 1). The 1,1-cyclobutanedicarboxylate ligand displays similar features to those described in the literature (Tu et al.,2004; Zhang et al., 2002; Ali et al.,2002). The six-membered chelate ring built up of the Pt(II) atom and the malonate anion adopts a boat conformation and the two symetry related 2-methylpyridine liagnds are oriented perpendicular to each other.

Related literature

For related literature, see: Ali et al. (2002); Jakuper et al. (2003); Tu et al. (2004); Zhang et al. (2002).

S2. Experimental

Potassium tetrachloroplatinate(II) (5 g, 12 mmol) was dissolved in water (50 ml) and KI (12 g, 72 mmol) was added. After standing in the dark for 30 min at room temperature, a solution of 2-methylpyridine (1.08 g, 12 mmol in 50 ml water) was added dropwise. The mixture was stirred for 4 h and the yellow precipitate of di(2-methylpyridine)PtI₂ was filtered off. Afterwards 2.5 g (0.044 mmol) of di(2-methylpyridine)PtI₂, 75 ml of water and disilver 1,1-cyclobutanedicarboxylate (1.07 g, 2.99 mmol) were stirred at 50 °C for 72 h. The precipitate of AgI was filtered off and the filtrate was concentrated at 40 °C under reduced pressure to about 5 ml until a white crystalline solid of the title compound precipitate. The compound was recrystallized from water to obtain crystals suitable for X-ray analysis.

S3. Refinement

All H atoms were initially located in a difference Fourier map but were positioned with idealized geometry and treated as riding on their parent atoms with C—H = 0.93 Å (aromatic), 0.96 Å (methyl) and 0.97 Å (methylene) and with U_iso(H) = 1.2U_eq(aromatic, methylene) and 1.5 for methyl H atoms) or U_iso(H) = 1.5U_eq(methyl).

The C10 atom is statistically distributed with respect to the crystallographic mirror plane. It was then refined using the PART -1 instruction within SHELXL97 (Sheldrick, 1997) and C—C restraints.

Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. Molecular view of the complex, with the atomic labeling scheme. Displacement ellipsoids are drawn at the 30% probability level. Only one component of the disordered moiety is represented. H atoms have been omitted for clarity. [Symmetry code: (i) x, –Y+3/2, z].

cis-(Cyclobutane-1,1-dicarboxylato)bis(2-methylpyridine)platinum(II)

Crystal data

[Pt(C6H6O4)(C6H7N)2]	F(000) = 1008
Mr = 523.45	Dx = 1.923 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P2ac2n	Cell parameters from 2278 reflections
a = 12.7339 (7) Å	θ = 2.5–28.3°
b = 14.5313 (8) Å	µ = 7.79 mm^−1
c = 9.7716 (6) Å	T = 298 K
V = 1808.14 (18) Å^3	Block, colourless
Z = 4	0.26 × 0.22 × 0.12 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	2278 independent reflections
Radiation source: fine-focus sealed tube	2031 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
φ and ω scans	θmax = 28.3°, θmin = 2.5°
Absorption correction: numerical (APEX2; Bruker, 2004)	h = −16→16
Tmin = 0.237, Tmax = 0.455	k = −19→19
14744 measured reflections	l = −12→12

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)] = 0.017	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.044	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.027P)^2 + 0.1067P] where P = (Fo^2 + 2Fc^2)/3
2278 reflections	(Δ/σ)max = 0.003
125 parameters	Δρmax = 0.78 e Å^−3
2 restraints	Δρmin = −0.66 e Å^−3

Special details

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.

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	Occ. (<1)
Pt1	0.615174 (10)	0.7500	0.091373 (11)	0.02943 (6)
N1	0.66661 (15)	0.64874 (13)	−0.03283 (19)	0.0326 (4)
O1	0.56091 (14)	0.65080 (11)	0.21436 (17)	0.0401 (4)
O2	0.50259 (19)	0.60774 (15)	0.41509 (18)	0.0605 (6)
C1	0.76953 (19)	0.62816 (18)	−0.0318 (3)	0.0401 (6)
H1	0.8138	0.6634	0.0227	0.048*
C2	0.8127 (3)	0.5579 (2)	−0.1070 (3)	0.0484 (7)
H2	0.8839	0.5442	−0.1011	0.058*
C3	0.7478 (2)	0.50885 (18)	−0.1906 (3)	0.0547 (8)
H3	0.7752	0.4629	−0.2464	0.066*
C4	0.6415 (2)	0.5272 (2)	−0.1925 (3)	0.0524 (7)
H4	0.5971	0.4929	−0.2483	0.063*
C5	0.6010 (2)	0.5970 (2)	−0.1110 (3)	0.0401 (6)
C6	0.4857 (2)	0.6157 (2)	−0.1055 (3)	0.0571 (8)
H6A	0.4658	0.6300	−0.0132	0.086*
H6B	0.4480	0.5624	−0.1360	0.086*
H6C	0.4694	0.6669	−0.1639	0.086*
C7	0.54870 (18)	0.66383 (16)	0.3446 (3)	0.0377 (5)
C8	0.5967 (3)	0.7500	0.4092 (3)	0.0397 (9)
C9	0.5995 (4)	0.7500	0.5655 (4)	0.0626 (14)
H9A	0.5886	0.8102	0.6059	0.075*	0.50
H9B	0.5538	0.7045	0.6070	0.075*	0.50
C11	0.7208 (4)	0.7500	0.4086 (4)	0.0517 (11)
H11A	0.7519	0.7040	0.3492	0.062*	0.50
H11B	0.7520	0.8101	0.3941	0.062*	0.50
C10	0.7137 (6)	0.7211 (7)	0.5593 (7)	0.097 (5)	0.50
H10A	0.7242	0.6557	0.5735	0.117*	0.50
H10B	0.7589	0.7567	0.6191	0.117*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pt1	0.02763 (8)	0.03190 (8)	0.02875 (8)	0.000	0.00074 (4)	0.000
N1	0.0328 (11)	0.0361 (10)	0.0290 (10)	−0.0017 (8)	0.0011 (8)	−0.0006 (8)
O1	0.0460 (10)	0.0357 (9)	0.0385 (9)	−0.0090 (7)	0.0058 (7)	0.0003 (7)
O2	0.0720 (16)	0.0569 (13)	0.0527 (13)	−0.0192 (11)	0.0175 (10)	0.0103 (9)
C1	0.0373 (14)	0.0443 (14)	0.0389 (14)	0.0011 (10)	−0.0007 (10)	−0.0031 (11)
C2	0.0447 (16)	0.0495 (16)	0.0510 (16)	0.0106 (13)	0.0063 (12)	−0.0044 (12)
C3	0.067 (2)	0.0439 (16)	0.0532 (17)	0.0066 (14)	0.0063 (14)	−0.0108 (12)
C4	0.0647 (19)	0.0453 (16)	0.0472 (16)	−0.0095 (13)	−0.0023 (13)	−0.0129 (13)
C5	0.0444 (16)	0.0387 (15)	0.0372 (14)	−0.0077 (11)	−0.0014 (10)	−0.0014 (11)
C6	0.0415 (17)	0.068 (2)	0.062 (2)	−0.0114 (15)	−0.0108 (13)	−0.0126 (14)
C7	0.0335 (13)	0.0376 (13)	0.0420 (14)	0.0011 (10)	0.0043 (10)	0.0044 (11)
C8	0.036 (2)	0.046 (2)	0.036 (2)	0.000	0.0050 (13)	0.000
C9	0.083 (4)	0.069 (3)	0.035 (2)	0.000	−0.003 (2)	0.000
C11	0.037 (2)	0.052 (2)	0.066 (3)	0.000	−0.0118 (17)	0.000
C10	0.089 (6)	0.140 (14)	0.062 (4)	0.003 (5)	−0.032 (4)	0.023 (5)

Geometric parameters (Å, º)

Pt1—O1^i	1.9999 (15)	C6—H6A	0.9600
Pt1—O1	1.9999 (15)	C6—H6B	0.9600
Pt1—N1	2.0167 (19)	C6—H6C	0.9600
Pt1—N1^i	2.0167 (19)	C7—C8	1.530 (3)
N1—C1	1.344 (3)	C8—C9	1.528 (5)
N1—C5	1.359 (3)	C8—C7^i	1.530 (3)
O1—C7	1.296 (3)	C8—C11	1.580 (6)
O2—C7	1.218 (3)	C9—C10^i	1.514 (8)
C1—C2	1.373 (4)	C9—C10	1.514 (8)
C1—H1	0.9300	C9—H9A	0.9700
C2—C3	1.363 (4)	C9—H9B	0.9700
C2—H2	0.9300	C11—C10^i	1.533 (7)
C3—C4	1.380 (4)	C11—C10	1.533 (7)
C3—H3	0.9300	C11—H11A	0.9700
C4—C5	1.389 (4)	C11—H11B	0.9700
C4—H4	0.9300	C10—H10A	0.9700
C5—C6	1.493 (4)	C10—H10B	0.9700
O1^i—Pt1—O1	92.24 (9)	O1—C7—C8	118.5 (2)
O1^i—Pt1—N1	178.71 (7)	C9—C8—C7	114.97 (19)
O1—Pt1—N1	87.02 (8)	C9—C8—C7^i	114.97 (19)
O1^i—Pt1—N1^i	87.02 (8)	C7—C8—C7^i	109.8 (3)
O1—Pt1—N1^i	178.71 (7)	C9—C8—C11	88.9 (3)
N1—Pt1—N1^i	93.71 (11)	C7—C8—C11	113.47 (19)
C1—N1—C5	118.7 (2)	C7^i—C8—C11	113.47 (19)
C1—N1—Pt1	118.33 (16)	C10^i—C9—C10	32.2 (8)
C5—N1—Pt1	122.83 (17)	C10^i—C9—C8	89.0 (4)
C7—O1—Pt1	121.76 (15)	C10—C9—C8	89.0 (4)
N1—C1—C2	123.5 (3)	C10^i—C9—H9A	84.5
N1—C1—H1	118.2	C10—C9—H9A	113.8
C2—C1—H1	118.2	C8—C9—H9A	113.8
C3—C2—C1	117.8 (3)	C10^i—C9—H9B	141.4
C3—C2—H2	121.1	C10—C9—H9B	113.8
C1—C2—H2	121.1	C8—C9—H9B	113.8
C2—C3—C4	120.2 (3)	H9A—C9—H9B	111.0
C2—C3—H3	119.9	C10^i—C11—C10	31.8 (8)
C4—C3—H3	119.9	C10^i—C11—C8	86.4 (4)
C3—C4—C5	119.8 (3)	C10—C11—C8	86.4 (4)
C3—C4—H4	120.1	C10^i—C11—H11A	142.0
C5—C4—H4	120.1	C10—C11—H11A	114.2
N1—C5—C4	119.9 (3)	C8—C11—H11A	114.2
N1—C5—C6	118.9 (2)	C10^i—C11—H11B	85.3
C4—C5—C6	121.3 (3)	C10—C11—H11B	114.2
C5—C6—H6A	109.5	C8—C11—H11B	114.2
C5—C6—H6B	109.5	H11A—C11—H11B	111.4
H6A—C6—H6B	109.5	C9—C10—C11	91.1 (4)
C5—C6—H6C	109.5	C9—C10—H10A	113.4
H6A—C6—H6C	109.5	C11—C10—H10A	113.4
H6B—C6—H6C	109.5	C9—C10—H10B	113.4
O2—C7—O1	121.0 (2)	C11—C10—H10B	113.4
O2—C7—C8	120.4 (2)	H10A—C10—H10B	110.7

Symmetry code: (i) x, −y+3/2, z.